Schedule of Restricted Share Unit Transactions [Abstract] Schedule of Restricted Share Unit Transactions [Abstract] Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Plan Name [Axis] Plan Name [Axis] Plan Name [Domain] Plan Name [Domain] Award Date [Axis] Award Date [Axis] Award Date [Domain] Award Date [Domain] Award Type [Axis] Award Type [Axis] Equity Award [Domain] Equity Award [Domain] Restricted Stock Units (RSUs) [Member] Restricted Stock Units (RSUs) [Member] Class of Stock [Axis] Class of Stock [Axis] Class of Stock [Domain] Class of Stock [Domain] Range [Axis] Range [Axis] Range [Domain] Range [Domain] Vesting [Axis] Vesting [Axis] Vesting [Domain] Vesting [Domain] Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Unvested balance at beginning of period Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number Weighted average grant date fair value, beginning of period Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value Shares granted Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period Weighted average grant date fair value, grants Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value Shares vested Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period Weighted average grant date fair value, vested Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Weighted Average Grant Date Fair Value Shares forfeited Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period Weighted average grant date fair value, forfeited Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeitures, Weighted Average Grant Date Fair Value Unvested balance at end of period Weighted average grant date fair value, end of period Compensation and Retirement Disclosure [Abstract] Schedule of Net Benefit Costs [Table Text Block] Schedule of Net Benefit Costs [Table Text Block] Fair Value Disclosures [Abstract] Fair Value Measurements [Text Block] Fair Value Disclosures [Text Block] Derivative Instruments and Hedging Activities Disclosure [Abstract] Derivative Instruments and Hedging Activities Disclosure [Text Block] Derivative Instruments and Hedging Activities Disclosure [Text Block] Organization, Consolidation and Presentation of Financial Statements [Abstract] Basis of Presentation [Text Block] Nature of Operations [Text Block] Fair Value, by Balance Sheet Grouping [Table] Fair Value, by Balance Sheet Grouping [Table] Oil and Gas Production Type [Axis] Oil and Gas Production Type [Axis] Production Type [Domain] Production Type [Domain] Proved Property [Member] Proved Property [Member] Proved Property [Member] Balance Sheet Location [Axis] Balance Sheet Location [Axis] Balance Sheet Location [Domain] Balance Sheet Location [Domain] Long-term [Member] Long term [Member] Derivative contracts with maturities in excess of one year. Short-term [Member] Short term [Member] Derivative contracts with maturities of one year or less. Fair Value, Hierarchy [Axis] Fair Value, Hierarchy [Axis] Fair Value, Measurements, Fair Value Hierarchy [Domain] Fair Value Hierarchy [Domain] Level 1 [Member] Fair Value, Inputs, Level 1 [Member] Level 2 [Member] Fair Value, Inputs, Level 2 [Member] Level 3 [Member] Fair Value, Inputs, Level 3 [Member] Netting Adjustments [Member] Netting Adjustments [Member] Netting Adjustments [Member] Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] Impairment of Oil and Gas Properties Impairment of Oil and Gas Properties Financial Assets Derivative Asset [Abstract] Derivative Asset, Fair Value, Gross Derivative Asset, Fair Value, Gross Asset Net amount of derivative assets presented on condensed consolidated balance sheets Derivative Asset, Fair Value, Amount Offset Against Collateral Financial liabilities Derivative Liability [Abstract] Derivative Liability, Fair Value, Gross Derivative Liability, Fair Value, Gross Liability Net amount of derivative liabilities presented on condensed consolidated balance sheets Derivative Liability, Fair Value, Amount Offset Against Collateral Subsequent Event [Abstract] Subsequent Event [Abstract] Subsequent Event [Table] Subsequent Event [Table] Subsequent Event Type [Axis] Subsequent Event Type [Axis] Subsequent Event Type [Domain] Subsequent Event Type [Domain] Subsequent Event [Line Items] Subsequent Event [Line Items] Subsequent Events [Text Block] Subsequent Events [Text Block] Disclosure of Compensation Related Costs, Share-based Payments [Abstract] Operating Activities [Axis] Operating Activities [Axis] Operating Activities [Domain] Operating Activities [Domain] Employee Stock Option [Member] Employee Stock Option [Member] Restricted Stock [Member] Restricted Stock [Member] Performance Share Units [Member] Performance Share Units [Member] Incremental common shares attributable to performance share units. Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Intrinsic Value Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Intrinsic Value Shares available for future grants Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant Share-based compensation Share-based Compensation Unrecognized compensation costs Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized Weighted average period for recognition of equity-based compensation expense Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition Award vesting period Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period Total fair value of stock that vested during the period Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Fair Value Schedule of Notional Amounts of Outstanding Derivative Positions [Table Text Block] Schedule of Notional Amounts of Outstanding Derivative Positions [Table Text Block] Schedule of Derivative Instruments in Statement of Financial Position, Fair Value [Table Text Block] Schedule of Derivative Instruments in Statement of Financial Position, Fair Value [Table Text Block] Derivative Instruments, Gain (Loss) [Table Text Block] Derivative Instruments, Gain (Loss) [Table Text Block] Document And Entity Information [Abstract] Document and Entity Information [Abstract] Entity Registrant Name Entity Registrant Name Entity Central Index Key Entity Central Index Key Current Fiscal Year End Date Current Fiscal Year End Date Entity Well-known Seasoned Issuer Entity Well-known Seasoned Issuer Entity Voluntary Filers Entity Voluntary Filers Entity Current Reporting Status Entity Current Reporting Status Entity Filer Category Entity Filer Category Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Document Fiscal Year Focus Document Fiscal Year Focus Document Fiscal Period Focus Document Fiscal Period Focus Document Type Document Type Amendment Flag Amendment Flag Document Period End Date Document Period End Date Asset Retirement Obligation [Abstract] Asset retirement obligations rollforward [Table Text Block] Schedule of Change in Asset Retirement Obligation [Table Text Block] Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward] Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward] Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Additional Disclosures [Abstract] Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Additional Disclosures [Abstract] Statement of Comprehensive Income [Abstract] Net income (loss) Net Income (Loss) Attributable to Parent Other comprehensive (loss) income, net of tax: Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest [Abstract] Pension and other postretirement plans adjustments: Other Comprehensive (Income) Loss, Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax [Abstract] Amortization of prior service costs Other Comprehensive (Income) Loss, Amortization Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, for Net Prior Service Cost (Credit), Net of Tax Amortization of net actuarial losses Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, for Net Gain (Loss), Net of Tax Other comprehensive income Other Comprehensive Income (Loss), Net of Tax Comprehensive income (loss) Comprehensive Income (Loss), Net of Tax, Attributable to Parent Amortization of prior service cost, income tax expense Other Comprehensive (Income) Loss, Amortization Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, for Net Prior Service Cost (Credit), Tax Amortization of net actuarial loss, income tax expense Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net Unamortized Gain (Loss) Arising During Period, Tax Share-Based Compensation [Text Block] Disclosure of Compensation Related Costs, Share-based Payments [Text Block] Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward] Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward] Outstanding at beginning of period Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number Options granted Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross Options cancelled Share-based Compensation Arrangement by Share-based Payment Award, Options, Other Increases (Decreases) in Period Outstanding at end of period Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract] Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract] Weighted average exercise price, beginning of year Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price Weighted average exercise price, granted in period Share-based Compensation Arrangements by Share-based Payment Award, Options, Grants in Period, Weighted Average Exercise Price Weighted average exercise price, canceled in period Share-based Compensation Arrangements by Share-based Payment Award, Options, Other Share Increase (Decrease) in Period, Weighted Average Exercise Price Weighted average exercise price, end of year Options exercisable, shares Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Number Options exercisable, weighted average exercise price Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Exercise Price Unvested options, shares Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested, Number of Shares Unvested options, weighted average exercise price Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested, Weighted Average Grant Date Fair Value Weighted average remaining contractual term, options outstanding Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term Weighted average remaining contractual term, options exercisable Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Remaining Contractual Term Weighted average remaining contractual term, options unvested Share Based Compensation Arrangement By Share Based Payment Award Options Unvested Weighted Average Remaining Contractual Term The weighted average period between the balance sheet date and expiration for all unvested portions of options outstanding under the plan, which may be expressed in a decimal value for number of years. Aggregate intrinsic value, options outstanding Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Intrinsic Value Aggregate intrinsic value, options exercisable Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Intrinsic Value Aggregate intrinsic value, options unvested Sharebased Compensation Arrangement By Sharebased Payment Award Options Unvested Intrinsic Value1 The total dollar difference between fair values of the underlying shares reserved for issuance and exercise prices of unvested portions of options outstanding and currently exercisable under the option plan as of the balance sheet date. Derivative [Table] Derivative [Table] Derivative Instrument Contract Type [Axis] Derivative Instrument Contract Type [Axis] Information by name that identifies a derivative or a group of derivatives by (derivative) contract risk type. Derivative Instrument Contract Type [Domain] Derivative Instrument Contract Type [Domain] The name that identifies a derivative or a group of derivatives, on a disaggregated basis, by contract risk type. Oil derivative contracts [Member] Oil derivative contracts [Member] Derivative instrument whose primary underlying risk is tied to commodity prices. Natural gas derivative contracts [Member] Natural gas derivative contracts [Member] Derivative instrument whose primary underlying risk is tied to commodity prices. Derivative Instrument [Axis] Derivative Instrument [Axis] Derivative Contract [Domain] Derivative Contract [Domain] Production [Member] Production [Member] Production [Member] Storage [Member] Storage [Member] Storage [Member] Income Statement Location [Axis] Income Statement Location [Axis] Income Statement Location [Domain] Income Statement Location [Domain] Derivative [Line Items] Derivative [Line Items] Realized gain (loss) on commodity derivative contracts not designated as hedging instruments Realized gain (loss) on commodity derivative contracts not designated as hedging instruments Represents the realized gain (loss) on commodity derivative contracts not designated as hedging instruments for the period. Unrealized gain (loss) on commodity derivative contracts not designated as hedging instruments Unrealized gain (loss) on commodity derivative contracts not designated as hedging instruments Represents the unrealized gain (loss) on commodity derivative contracts not designated as hedging instruments for the period. Realized and Unrealized Gain (Loss) on Commodity Derivative Contracts Not Designated as Hedging Instruments Realized and Unrealized Gain (Loss) on Commodity Derivative Contracts Not Designated as Hedging Instruments Total Realized and Unrealized Gain (Loss) on Commodity Derivative Contracts Not Designated as Hedging Instruments Statement of Financial Position [Abstract] LIABILITIES AND EQUITY Liabilities and Equity [Abstract] EQUITY Stockholders' Equity Attributable to Parent [Abstract] Common stock, par value (in dollars per share) Common Stock, Par or Stated Value Per Share Common stock, shares authorized (in shares) Common Stock, Shares Authorized Common stock, shares issued (in shares) Common Stock, Shares, Issued Treasury stock (in shares) Treasury Stock, Shares Share-based Compensation Expense [Table] Share-based Compensation Expense [Table] Share-based Compensation Expense [Table] Share-based Compensation Expense [Line Items] Share-based Compensation Expense [Line Items] [Line Items] for Share-based Compensation Expense [Table] Share-based Compensation Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost Share-based Compensation Expense [Table Text Block] Share-based Compensation Expense [Table Text Block] [Table Text Block] for Share-based Compensation Expense [Table] Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions [Table Text Block] Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions [Table Text Block] Schedule of Share-based Compensation, Stock Options, Activity [Table Text Block] Schedule of Share-based Compensation, Stock Options, Activity [Table Text Block] Schedule of Share-based Compensation, Restricted Share Awards Activity [Table Text Block] Schedule of Share-based Compensation, Restricted Stock and Restricted Stock Units Activity [Table Text Block] Schedule of Other Share-based Compensation, Activity [Table Text Block] Schedule of Other Share-based Compensation, Activity [Table Text Block] Debt Disclosure [Abstract] Debt [Text Block] Debt Disclosure [Text Block] Statement of Equity [Abstract] Statement of Equity [Abstract] Statement [Table] Statement [Table] Scenario [Axis] Scenario [Axis] Scenario, Unspecified [Domain] Scenario, Unspecified [Domain] Report Date [Axis] Report Date [Axis] Financial Statement Filing Date [Domain] Financial Statement Filing Date [Domain] Equity Components [Axis] Equity Components [Axis] Equity Component [Domain] Equity Component [Domain] Common Stock, Value [Member] Common Stock, Value [Member] Common Stock, Value [Member] Treasury Stock [Member] Treasury Stock [Member] Additional Paid-in Capital [Member] Additional Paid-in Capital [Member] Retained Earnings [Member] Retained Earnings [Member] Accumulated Other Comprehensive Income (Loss) [Member] Other Comprehensive Income (Loss) [Member] Adjustments for New Accounting Pronouncements [Axis] Adjustments for New Accounting Pronouncements [Axis] Type of Adoption [Domain] Type of Adoption [Domain] Adjustments for Change in Accounting Principle [Axis] Adjustments for Change in Accounting Principle [Axis] Adjustments for Change in Accounting Principle [Domain] Adjustments for Change in Accounting Principle [Domain] Adjustments for Error Corrections [Axis] Adjustments for Error Corrections [Axis] Adjustments for Error Correction [Domain] Adjustments for Error Correction [Domain] Statement [Line Items] Statement [Line Items] Stockholders' Equity Stockholders' Equity Attributable to Parent Shares, Issued Shares, Issued Treasury Stock, Shares Net income Stockholders' Equity, Other Shares Stockholders' Equity, Other Shares Stock Issued During Period, Shares, New Issues Stock Issued During Period, Shares, New Issues Stock Issued During Period, Value, New Issues Stock Issued During Period, Value, New Issues Stock Issued During Period, Shares, Treasury Stock Reissued Stock Issued During Period, Shares, Treasury Stock Reissued Stock Granted, Value, Share-based Compensation, Net of Forfeitures Stock Granted, Value, Share-based Compensation, Net of Forfeitures Stock Issued During Period, Shares, Share-based Compensation, Net of Forfeitures Stock Issued During Period, Shares, Share-based Compensation, Net of Forfeitures Stock Issued During Period, Value, Share-based Compensation, Net of Forfeitures Stock Issued During Period, Value, Share-based Compensation, Net of Forfeitures Other Comprehensive (Income) Loss, Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax Other Comprehensive (Income) Loss, Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax Stockholders' Equity Shares, Issued Treasury Stock, Shares Schedule of Stock Issuance [Table] Schedule of Stock Issuance [Table] Schedule of Stock Issuance [Table] Share Issuance [Axis] Share Issuance [Axis] Share Issuance [Axis] Share Issuance [Domain] Share Issuance [Domain] [Domain] for Share Issuance [Axis] Share Issuance - June 2016 [Domain] Share Issuance - June 2016 [Domain] Share Issuance - June 2016 [Domain] Share Issuance - March 2016 [Domain] Share Issuance - March 2016 [Domain] Share Issuance - March 2016 [Domain] Schedule of Stock Issuance [Line Items] Schedule of Stock Issuance [Line Items] [Line Items] for Schedule of Stock Issuance [Table] Common Stock, Shares Issued in Period Common Stock, Shares Issued in Period Common Stock, Shares Issued in Period Proceeds from Issuance of Common Stock Proceeds from Issuance of Common Stock Statement of Cash Flows [Abstract] OPERATING ACTIVITIES Net Cash Provided by (Used in) Operating Activities [Abstract] Adjustments to reconcile net income (loss) to net cash provided by operating activities: Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract] Depreciation, depletion and amortization Depreciation, Depletion and Amortization Deferred income taxes Deferred Income Tax Expense (Benefit) Impairment Asset Impairment Charges Bargain purchase gain from acquisition Business Combination, Bargain Purchase, Gain Recognized, Amount Other Operating Activities, Curtailment Loss Other Operating Activities, Curtailment Loss Other Operating Activities, Curtailment Loss Amortization of debt issuance costs and discounts Amortization of Debt Issuance Costs and Discounts Net (gain) loss from asset sales Gain (Loss) on Disposition of Property Plant Equipment, Excluding Oil and Gas Property and Timber Property Unrealized (gains) losses on marketable securities Marketable Securities, Unrealized Gain (Loss), Excluding Other than Temporary Impairments Unrealized (gains) losses on derivative contracts Unrealized Gain (Loss) on Derivatives Changes in operating assets and liabilities Increase (Decrease) in Operating Capital Net Cash Provided by (Used in) Operating Activities Net Cash Provided by (Used in) Operating Activities, Continuing Operations INVESTING ACTIVITIES Net Cash Provided by (Used in) Investing Activities [Abstract] Property acquisitions Payments to Acquire Oil and Gas Property Acquisition Deposit Held In Escrow Acquisition Deposit Held In Escrow acquisition deposit held in escrow Property, plant and equipment, including dry exploratory well expense Payments to Acquire Oil and Gas Equipment Proceeds from disposition of assets Proceeds from Sale of Oil and Gas Property and Equipment Net Cash Provided by (Used in) Investing Activities Net Cash Provided by (Used in) Investing Activities, Continuing Operations FINANCING ACTIVITIES Net Cash Provided by (Used in) Financing Activities [Abstract] Checks outstanding in excess of cash balances Increase (Decrease) in Outstanding Checks, Financing Activities Repayments of Long-term Debt Repayments of Long-term Debt Treasury stock repurchases Payments for Repurchase of Common Stock Dividends paid Payments of Ordinary Dividends, Common Stock Proceeds from issuance of common stock, net Excess tax (provision) benefit on share-based compensation Excess tax (provision) benefit on share-based compensation Excess tax (provision) benefit on share-based compensation Net Cash Provided by (Used in) Financing Activities Net Cash Provided by (Used in) Financing Activities, Continuing Operations Change in cash and cash equivalents Cash and Cash Equivalents, Period Increase (Decrease) Beginning cash and cash equivalents Cash and Cash Equivalents, at Carrying Value Ending cash and cash equivalents Supplemental Disclosures: Supplemental Cash Flow Elements [Abstract] Cash paid for interest, net of capitalized interest Interest Paid, Net Cash paid (refund received) for income taxes Income Taxes Paid, Net Non-cash Investing Activities Noncash Investing and Financing Items [Abstract] Change in capital expenditure accruals and other non-cash adjustments Capital Expenditures Incurred but Not yet Paid Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Table] Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Table] Defined Benefit Plans and Other Postretirement Benefit Plans [Axis] Defined Benefit Plans and Other Postretirement Benefit Plans [Axis] Defined Benefit Plan and Other Postretirement Benefit Plan [Domain] Defined Benefit Plan and Other Postretirement Benefit Plan [Domain] Funded Pension Plan [Member] Funded Pension Plan [Member] Information on funded defined benefit pension plan. Unfunded Pension Plan [Member] Unfunded Pension Plan [Member] Information on unfunded defined benefit pension plan. Other Postretirement Benefit Plan [Member] Other Postretirement Benefit Plan [Member] Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] Pension Contributions Pension Contributions Defined Benefit Plans, Estimated Future Employer Contributions in Current Fiscal Year Defined Benefit Plans, Estimated Future Employer Contributions in Current Fiscal Year Other Postretirement Benefits Payments Other Postretirement Benefits Payments Revision of Financial Statements [Table] Revision of Financial Statements [Table] As reported [Member] As reported [Member] As reported [Member] As revised [Member] As revised [Member] As revised [Member] Change [Member] Change [Member] Change [Member] Revision of Financial Statements [Line Items] Revision of Financial Statements [Line Items] [Line Items] for Revision of Financial Statements [Table] Revenue from Purchased Oil and Gas Revenue from Purchased Oil and Gas Revenues Revenues Cost of Purchased Oil and Gas Cost of Purchased Oil and Gas Operating Expenses Operating Expenses Income Statement [Abstract] REVENUES Revenues [Abstract] Gas sales Natural Gas Production Revenue Oil sales Oil and Condensate Revenue NGL sales Natural Gas Midstream Revenue Other revenue Gas Gathering, Transportation, Marketing and Processing Revenue Purchased gas and oil sales Refining and Marketing Revenue Total Revenues Oil and Gas Revenue OPERATING EXPENSES Operating Expenses [Abstract] Purchased gas and oil expense Refining and Marketing Costs Lease operating expense Oil and Gas Property, Lease Operating Expense Gas, oil and NGL transportation and other handling costs Shipping, Handling and Transportation Costs Gathering and other expense Gas Gathering, Transportation, Marketing and Processing Costs General and administrative General and Administrative Expense Production and property taxes Production Tax Expense Depreciation, depletion and amortization Results of Operations, Depreciation, Depletion, Amortization and Accretion Exploration expenses Exploration Expense Total operating expenses Net gain (loss) from asset sales Gain (Loss) on Disposition of Property Plant Equipment OPERATING INCOME (LOSS) Operating Income (Loss) Realized and unrealized gains (losses) on derivative contracts (Note 7) Gain on Derivative Instruments, Pretax Interest and other income (expense) Interest Income, Operating Interest expense Interest Expense INCOME (LOSS) BEFORE INCOME TAXES Results of Operations, Income before Income Taxes Income tax (provision) benefit Income Tax Expense (Benefit) NET INCOME (LOSS) Earnings per common share Earnings Per Share [Abstract] Earnings Per Share, Basic Earnings Per Share, Basic Earnings Per Share, Diluted Earnings Per Share, Diluted Weighted-average common shares outstanding Weighted Average Number of Shares Outstanding, Diluted [Abstract] Used in basic calculation (in shares) Weighted Average Number of Shares Outstanding, Basic Used in diluted calculation (in shares) Weighted Average Number of Shares Outstanding, Diluted Dividends per common share (in dollars per share) Common Stock, Dividends, Per Share, Cash Paid Asset Retirement Obligations [Text Block] Asset Retirement Obligation Disclosure [Text Block] Capitalized Exploratory Well Costs [Abstract] Capitalized Exploratory Well Costs [Table Text Block] Capitalized Exploratory Well Costs [Table Text Block] [Table Text Block] for Capitalized Exploratory Well Costs [Table] Business Combinations [Abstract] Acquisitions & Divestitures [Text Block] Mergers, Acquisitions and Dispositions Disclosures [Text Block] Earnings Per Share [Text Block] Earnings Per Share [Text Block] Components of basic and diluted shares used in EPS [Table Text Block] Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Proceeds from Sale of Oil and Gas Property and Equipment Schedule of Business Acquisitions [Table] Schedule of Business Acquisitions, by Acquisition [Table] Business Acquisition [Axis] Business Acquisition [Axis] Business Acquisition, Acquiree [Domain] Business Acquisition, Acquiree [Domain] Property, Plant and Equipment, Type [Axis] Property, Plant and Equipment, Type [Axis] Property, Plant and Equipment, Type [Domain] Property, Plant and Equipment, Type [Domain] Permian Basin Acquisition [Member] Permian Basin Acquisition [Member] Permian Basin Acquisition [Member] Williston & Permian Basins [Member] Williston & Permian Basins [Member] Williston & Permian Basins [Member] Business Acquisition [Line Items] Business Acquisition [Line Items] Acquisition Costs, Period Cost Acquisition Costs, Period Cost Bargain purchase gain from acquisition Net Acres Net Acres Net Acres Goodwill, Acquired During Period Goodwill, Acquired During Period Restructuring and Related Activities [Abstract] Schedule of Restructuring and Related Costs [Table] Schedule of Restructuring and Related Costs [Table] Segments [Axis] Segments [Axis] Segments [Domain] Segments [Domain] Denver Restructuring [Member] Denver Restructuring [Member] Denver Restructuring [Member] Tulsa Regional Office [Member] Tulsa Regional Office [Member] Tulsa Regional Office [Member] Restructuring Type [Axis] Restructuring Type [Axis] Type of Restructuring [Domain] Type of Restructuring [Domain] One-time Termination Benefits [Member] One-time Termination Benefits [Member] Employee Relocation [Member] Employee Relocation [Member] Restructuring Cost and Reserve [Line Items] Restructuring Cost and Reserve [Line Items] Reduction of Employees - Restructuring Reduction of Employees - Restructuring Reduction of Employees - Restructuring Restructuring and Related Cost, Expected Cost Restructuring and Related Cost, Expected Cost Restructuring and Related Cost, Incurred Cost Restructuring and Related Cost, Incurred Cost Schedule of Error Corrections and Prior Period Adjustment Restatement [Table] Schedule of Error Corrections and Prior Period Adjustment Restatement [Table] Error Corrections and Prior Period Adjustments Restatement [Line Items] Error Corrections and Prior Period Adjustments Restatement [Line Items] Schedule of Error Corrections and Prior Period Adjustments [Table Text Block] Schedule of Error Corrections and Prior Period Adjustments [Table Text Block] Long-term Debt, Type [Axis] Long-term Debt, Type [Axis] Long-term Debt, Type [Domain] Long-term Debt, Type [Domain] Minimum [Member] Minimum [Member] Maximum [Member] Maximum [Member] Maximum Forecasted Production Covered By Derivatives Maximum Forecasted Production Covered By Derivatives Potential maximum amount of forecasted production covered by derivative contracts. Expected Annual Production Covered By Derivatives Expected Annual Production Covered By Derivatives Expected Annual Production Covered By Derivatives Gas Swaps [Member] Gas Swaps [Member] Gas Swaps [Member] Oil Swaps [Member] Oil Swaps [Member] Oil Swaps [Member] Gas Collars [Member] Gas Collars [Member] Gas Collars [Member] Gas Basis Swaps [Member] Gas Basis Swaps [Member] Gas Basis Swaps [Member] Gas Purchase Swaps [Member] Gas Purchase Swaps [Member] Gas Purchase Swaps [Member] Derivative Contract Year [Axis] Derivative Contract Year [Axis] Tabular presentation of derivative instruments by year of contract. Derivative Contract Year [Domain] Derivative Contract Year [Domain] Tabular presentation of derivative instruments by year of contract. Year 2016 [Member] Year 2016 [Member] Year 2016 [Member] Year 2017 [Member] Year 2017 [Member] Year 2017 [Member] Year 2018 [Member] Year 2018 [Member] Year 2018 [Member] Energy Commodities Exchange [Axis] Energy Commodities Exchange [Axis] Exchange where various commodities and derivatives products are traded Energy Commodities Exchange Abbreviation [Domain] Energy Commodities Exchange Abbreviation [Domain] Exchange abbreviation where various commodities and derivatives products are traded. NYMEX HH [Member] NYMEX HH [Member] NYMEX HH [Member] IFNPCR [Member] IFNPCR [Member] Energy Commodities Exchange Abbreviation NYMEX WTI [Member] NYMEX WTI [Member] Energy Commodities Exchange Abbreviation NYMEX HH LESS IFNPCR [Member] NYMEX HH LESS IFNPCR [Member] NYMEX HH LESS IFNPCR [Member] Derivative Volumes Derivative, Nonmonetary Notional Amount Average Swap Price per Unit Average Swap Price per Unit Average Swap Price per Unit Weighted-Average Differential Underlying, Derivative Derivative Average Price Floor Derivative Average Price Floor Derivative Average Price Floor Derivative Average Price Ceiling Derivative Average Price Ceiling Derivative Average Price Ceiling Restructuring and Related Activities Disclosure [Text Block] Restructuring and Related Activities Disclosure [Text Block] Asset Retirement Obligation, Current Asset Retirement Obligation, Current ARO Liability [Roll Forward] Asset Retirement Obligation, Roll Forward Analysis [Roll Forward] ARO liability, Beginning Balance Asset Retirement Obligation Accretion Asset Retirement Obligation, Accretion Expense Additions Asset Retirement Obligation, Liabilities Incurred Asset Retirement Obligation, Revision of Estimate Asset Retirement Obligation, Revision of Estimate Liabilities settled Asset Retirement Obligation, Liabilities Settled ARO liability, Ending Balance Commitments and Contingencies Disclosure [Abstract] Commitment and Contingencies [Text Block] Commitments and Contingencies Disclosure [Text Block] Loss Contingencies [Table] Loss Contingencies [Table] Litigation Case [Axis] Litigation Case [Axis] Litigation Case [Domain] Litigation Case [Domain] Rocky Mountain Resources Lawsuit [Member] Rocky Mountain Resources Lawsuit [Member] Rocky Mountain Resources Lawsuit [Member] Litigation Status [Axis] Litigation Status [Axis] Litigation Status [Domain] Litigation Status [Domain] Loss Contingency Nature [Axis] Loss Contingency Nature [Axis] Loss Contingency, Nature [Domain] Loss Contingency, Nature [Domain] Loss Contingencies [Line Items] Loss Contingencies [Line Items] Litigation Settlement, Amount Litigation Settlement, Amount Litigation Settlement Statutory Interest Rate Litigation Settlement Statutory Interest Rate Litigation Settlement Statutory Interest Rate Loss Contingency Bond Posted Loss Contingency Bond Posted Loss Contingency Bond Posted Overriding Royalty Interest Overriding Royalty Interest Overriding Royalty Interest Loss on Contingency, Estimate of Possible Loss, Minimum Loss on Contingency, Estimate of Possible Loss, Minimum Loss on Contingency, Estimate of Possible Loss, Minimum Loss Contingency, Estimate of Possible Loss, Maximum Loss Contingency, Estimate of Possible Loss, Maximum Loss Contingency, Estimate of Possible Loss, Maximum Capitalized exploratory well costs, beginning balance Capitalized Exploratory Well Costs Additions to capitalized exploratory well costs pending the determination of proved reserves Capitalized Exploratory Well Cost, Period Increase (Decrease) Reclassification to proved properties after the determination of proved reserves Reclassification to Well, Facilities, and Equipment Based on Determination of Proved Reserves Capitalized exploratory well costs charged to expense Capitalized Exploratory Well Cost, Charged to Expense Capitalized exploratory well costs, ending balance Employee Benefits [Text Block] Pension and Other Postretirement Benefits Disclosure [Text Block] Schedule of Long-term Debt Instruments [Table] Schedule of Long-term Debt Instruments [Table] Revolving Credit Facility due 2019 [Member] Line of Credit [Member] 6.05% Senior Notes due 2016 [Member] Senior Notes Due 2016 [Member] Senior Notes Due 2016. 6.80% Senior Notes due 2018 [Member] Senior Notes Due 2018 [Member] Senior Notes Due 2018. 6.80% Senior Notes Due 2020 [Member] Senior Notes Due 2020 [Member] Senior Notes Due 2020. 6.875% Senior Notes Due 2021 [Member] Senior Notes Due 2021 [Member] Senior Notes Due 2021. Debt Instrument [Line Items] Debt Instrument [Line Items] Long-term Debt, Gross Long-term Debt, Gross Long-term debt, interest rate (in hundredths) Debt Instrument, Interest Rate, Stated Percentage Maturity date of long-term debt Debt Instrument, Maturity Date Debt Maturity Period Debt Maturity Period Debt Maturity Period Borrowing capacity Line of Credit Facility, Current Borrowing Capacity Letters of credit outstanding Letters of Credit Outstanding, Amount Principal amount of senior notes outstanding Senior Notes Debt Instrument, Maturity Date Range, Start Debt Instrument, Maturity Date Range, Start Debt Instrument, Maturity Date Range, End Debt Instrument, Maturity Date Range, End Senior Notes, stated interest rate, minimum (in hundredths) Debt instrument, Stated Rate Range, Minimum Debt instrument, Stated Rate Range, Minimum Senior Notes, stated interest rate, maximim (in hundredths) Debt Instrument, Stated Rate Range, Maximum Debt Instrument, Stated Rate Range, Maximum Fair Value Measurements, Recurring and Nonrecurring [Table] Fair Value Measurements, Recurring and Nonrecurring [Table] Measurement Frequency [Axis] Measurement Frequency [Axis] Fair Value, Measurement Frequency [Domain] Fair Value, Measurement Frequency [Domain] Fair Value Hierarchy [Domain] Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Fair value of financial assets and liabilities [Table Text Block] Fair Value Measurements, Recurring and Nonrecurring [Table Text Block] Fair value and related carrying amount of certain financial instruments [Table Text Block] Fair Value, by Balance Sheet Grouping [Table Text Block] Anti-dilutive shares Anti-dilutive shares Anti-dilutive shares Weighted-average basic common shares outstanding Potential number of shares issuable upon exercise of in-the-money stock options under the Long-term Stock Incentive Plan Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements Average diluted common shares outstanding Debt Outstanding [Table Text Block] Schedule of Debt [Table Text Block] Pension Plan [Member] Pension Plan [Member] Service cost Defined Benefit Plan, Service Cost Interest cost Defined Benefit Plan, Interest Cost Expected return on plan assets Defined Benefit Plan, Expected Return on Plan Assets Amortization of prior service costs Defined Benefit Plan, Amortization of Prior Service Cost (Credit) Amortization of actuarial losses Defined Benefit Plan, Amortization of Gains (Losses) Curtailment loss Defined Benefit Plan, Recognized Net Gain (Loss) Due to Curtailments Periodic expense Defined Benefit Plan, Net Periodic Benefit Cost Condensed Balance Sheet Statements, Captions [Line Items] Condensed Balance Sheet Statements, Captions [Line Items] ASSETS Assets [Abstract] Current Assets Assets, Current [Abstract] Cash and cash equivalents Accounts receivable, net Accounts Receivable, Net, Current Income tax receivable Income Taxes Receivable, Current Fair value of derivative contracts Derivative Instruments and Hedges, Assets Gas, oil and NGL inventories at lower of average cost or market Energy Related Inventory Prepaid expenses and other Prepaid Expense and Other Assets, Current Total Current Assets Assets, Current Property, Plant and Equipment (successful efforts method for oil and gas properties) Oil and Gas Property, Successful Effort Method, Net [Abstract] Property, Plant and Equipment (successful efforts method for gas and oil properties) Property, Plant and Equipment, Net [Abstract] Proved properties Proved Oil and Gas Property, Successful Effort Method Unproved properties Unproved Oil and Gas Property, Successful Effort Method Marketing and other Property, Plant and Equipment, Other, Gross Material and supplies Inventory, Drilling, Noncurrent Total Property, Plant and Equipment Property, Plant and Equipment, Gross Less Accumulated Depreciation, Depletion and Amortization Oil and Gas Property, Successful Effort Method, Accumulated Depreciation, Depletion Amortization and Impairment [Abstract] Less Accumulated Depreciation, Depletion and Amortization Depreciation, Depletion and Amortization, Nonproduction [Abstract] Exploration and production Oil and Gas Property, Successful Effort Method, Accumulated Depreciation, Depletion and Amortization Marketing and other Property, Plant and Equipment, Other, Accumulated Depreciation Total Accumulated Depreciation, Depletion and Amortization Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment Net Property, Plant and Equipment Property, Plant and Equipment, Net Fair value of derivative contracts Derivative Instruments and Hedges, Noncurrent Other noncurrent assets Other Assets, Noncurrent TOTAL ASSETS Assets Current Liabilities Liabilities, Current [Abstract] Checks outstanding in excess of cash balances Bank Overdrafts Accounts payable and accrued expenses Accounts Payable and Accrued Liabilities, Current Production and property taxes Accrual for Taxes Other than Income Taxes, Current Interest payable Interest Payable, Current Fair value of derivative contracts Derivative Liability, Current Deferred income taxes Deferred Tax Liabilities, Net, Current Current portion of long-term debt Long-term Debt, Current Maturities Total Current Liabilities Liabilities, Current Long-term debt Long-term Debt, Excluding Current Maturities Deferred income taxes Deferred Tax Liabilities, Net, Noncurrent Asset retirement obligations Asset Retirement Obligations, Noncurrent Fair value of derivative contracts Derivative Liability, Noncurrent Other long-term liabilities Other Liabilities, Noncurrent Commitments and contingencies (Note 10) Commitments and Contingencies Common stock – par value $0.01 per share; 500.0 million shares authorized; 240.7 million and 177.3 million shares issued, respectively Common Stock, Value, Issued Treasury stock – 1.1 million and 0.5 million shares, respectively Treasury Stock, Value Additional paid-in capital Additional Paid in Capital, Common Stock Retained earnings Retained Earnings (Accumulated Deficit) Accumulated other comprehensive income (loss) Accumulated Other Comprehensive Income (Loss), Net of Tax Total Shareholders' Equity TOTAL LIABILITIES AND EQUITY Liabilities and Equity Equity [Abstract] Equity [Abstract] Fair Value, Measurements, Recurring [Member] Fair Value, Measurements, Recurring [Member] Measurement Basis [Axis] Measurement Basis [Axis] Fair Value Measurement [Domain] Fair Value Measurement [Domain] Portion at Fair Value Measurement [Member] Portion at Fair Value Measurement [Member] Reported Value Measurement [Member] Reported Value Measurement [Member] Estimate of Fair Value Measurement [Member] Estimate of Fair Value Measurement [Member] Derivative Asset, Fair Value, Gross Asset Cash and Cash Equivalents, at Carrying Value Long-term debt Long-term Debt Long-term debt, fair value Long-term Debt, Fair Value Schedule of Impaired Long-Lived Assets Held and Used [Table] Schedule of Impaired Long-Lived Assets Held and Used [Table] Geographical [Axis] Geographical [Axis] Geographical [Domain] Geographical [Domain] Pinedale [Member] Pinedale [Member] Pinedale [Member] Other Northern [Member] Other Northern [Member] Other Northern [Member] Other Southern [Member] Other Southern [Member] Other Southern [Member] Unproved Property [Member] Unproved Property [Member] Unproved Property [Member] Impaired Long-Lived Assets Held and Used [Line Items] Impaired Long-Lived Assets Held and Used [Line Items] Weighted-average grant-date fair value of awards granted during the period Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value Weighted-average risk-free interest rate Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Risk Free Interest Rate Weighted-average expected price volatility Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Weighted Average Volatility Rate Expected dividend yield Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Dividend Rate Expected term in years at the date of grant Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Term Fair Value, Inputs, Level 2 [Member] Commodity Contract [Member] Commodity Contract [Member] Senior Notes Due 2016 [Member] Senior Notes Due 2018 [Member] Senior Notes Due 2020 [Member] Senior Notes Due 2022 [Member] Senior Notes Due 2022 [Member] Senior Notes Due 2022. 5.25% Senior Notes Due 2023 [Member] 5.25% Senior Notes Due 2023 [Member] 5.25% Senior Notes Due 2023 [Member] Less unamortized discount Debt Instrument, Unamortized Discount Less: current portion of long-term debt Unsecured Debt, Current Total long-term debt outstanding Capitalized Exploratory Well Costs [Table] Capitalized Exploratory Well Costs [Table] Capitalized Exploratory Well Costs [Table] Capitalized Exploratory Well Costs [Line Items] Capitalized Exploratory Well Costs [Line Items] [Line Items] for Capitalized Exploratory Well Costs [Table] Capitalized Exploratory Well Costs [Text Block] Capitalized Exploratory Well Costs [Text Block] Capitalized Exploratory Well Costs [Text Block]