Statement of Comprehensive Income [Abstract] Statement [Table] Statement [Table] Scenario [Axis] Scenario [Axis] Scenario, Unspecified [Domain] Scenario, Unspecified [Domain] Statement [Line Items] Statement [Line Items] Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net Unamortized Gain (Loss) Arising During Period, Net of Tax Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net Unamortized Gain (Loss) Arising During Period, Net of Tax Postretirement medical plan changes, income tax expense Other Comprehensive (Income) Loss, Reclassification Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, Tax 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 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 Business Combinations [Abstract] Acquisitions & Divestitures [Text Block] Mergers, Acquisitions and Dispositions Disclosures [Text Block] Restructuring [Abstract] Restructuring [Abstract] Statement of Financial Position [Abstract] 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 Cash and Cash Equivalents, at Carrying Value Accounts receivable, net Accounts Receivable, Net, Current Income tax receivable Income Taxes Receivable, Current Fair value of derivative contracts Derivative Asset, Current Hydrocarbon inventories, at lower of average cost or net realizable value Energy Related Inventory Prepaid expenses Prepaid Expense, Current Other current assets Other Assets, Current Total Current Assets Assets, Current Property, Plant and Equipment (successful efforts method for oil and gas 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 Gathering and other Property, Plant and Equipment, Other, Gross Materials and supplies Inventory, Drilling, Noncurrent Total Property, Plant and Equipment Property, Plant and Equipment, Gross 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 Gathering 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 LIABILITIES AND EQUITY Liabilities and Equity [Abstract] Current Liabilities Liabilities, Current [Abstract] Checks outstanding in excess of cash balances Bank Overdrafts Accounts payable 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 Other current liabilities Other Liabilities, Current 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 EQUITY Stockholders' Equity Attributable to Parent [Abstract] Common stock – par value $0.01 per share; 500.0 million shares authorized; 240.3 million and 243.0 million shares issued, respectively Common Stock, Value, Issued Treasury stock – 2.6 million and 2.0 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 Common Shareholders' Equity Stockholders' Equity Attributable to Parent TOTAL LIABILITIES AND EQUITY Liabilities and Equity Revenue Recognition [Abstract] Revenue Recognition 606 [Table Text Block] Revenue Recognition 606 [Table Text Block] Revenue Recognition 606 [Table Text Block] Revenue Recognition [Table Text Block] Revenue Recognition [Table Text Block] [Table Text Block] for Revenue Recognition [Table] Commitments and Contingencies Disclosure [Abstract] Commitment and Contingencies [Text Block] Commitments and Contingencies Disclosure [Text Block] Earnings Per Share [Abstract] Components of basic and diluted shares used in EPS [Table Text Block] Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Derivative Instruments and Hedging Activities Disclosure [Abstract] 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. Gas Swaps [Member] Gas Swaps [Member] Gas Swaps [Member] Oil Swaps [Member] Oil Swaps [Member] Oil Swaps [Member] Oil Basis Swaps [Member] Oil Basis Swaps [Member] Oil Basis Swaps [Member] Gas Basis Swaps [Member] Gas Basis Swaps [Member] Gas Basis 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 2018 [Member] Year 2018 [Member] Year 2018 [Member] Year 2018 (July through December) [Member] Year 2018 (July through December) [Member] Year 2018 (July through December) [Member] Year 2019 [Member] Year 2019 [Member] Year 2019 [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 WTI [Member] NYMEX WTI [Member] Energy Commodities Exchange Abbreviation NYMEX HH [Member] NYMEX HH [Member] NYMEX HH [Member] NYMEX WTI less Argus WTI Midland [Member] NYMEX WTI less Argus WTI Midland [Member] NYMEX WTI less Argus WTI Midland [Member] NYMEX HH LESS IFNPCR [Member] NYMEX HH LESS IFNPCR [Member] NYMEX HH LESS IFNPCR [Member] Derivative [Line Items] Derivative [Line Items] 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 Asset Retirement Obligation [Abstract] Asset Retirement Obligations [Text Block] Asset Retirement Obligation Disclosure [Text Block] Disclosure of Compensation Related Costs, Share-based Payments [Abstract] Share-Based Compensation [Text Block] Disclosure of Compensation Related Costs, Share-based Payments [Text Block] Net income (loss) Net Income (Loss) Attributable to Parent Postretirement medical plan change(1) Other Comprehensive (Income) Loss, Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax Fair value of plan assets adjustment(2) Defined Benefit Plan, Fair Value of Plan Assets, Period Increase (Decrease) Amortization of prior service costs(3) 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 actuarial losses(4) 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 Derivative Instruments and Hedging Activities Disclosure [Text Block] Derivative Instruments and Hedging Activities Disclosure [Text Block] Compensation and Retirement Disclosure [Abstract] Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Table] Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Table] Business Divestiture [Axis] Business Divestiture [Axis] Business Divestiture [Axis] Business Divestiture [Domain] Business Divestiture [Domain] [Domain] for Business Divestiture [Axis] Pinedale Divestiture [Member] Pinedale Divestiture [Member] Pinedale Divestiture [Member] 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] Pension Plan [Member] Pension Plan [Member] SERP [Member] SERP [Member] SERP [Member] Medical Plan [Member] Medical Plan [Member] Medical 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] Contributions by Employer Defined Benefit Plan, Contributions by Employer Estimated Future Employer Contributions in Current Fiscal Year Defined Benefit Plans, Estimated Future Employer Contributions in Current Fiscal Year Curtailment loss Defined Benefit Plan, Curtailments Asset retirement obligations rollforward [Table Text Block] Schedule of Change in Asset Retirement Obligation [Table Text Block] Divestitures [Table] Divestitures [Table] Divestitures [Table] Divestitures [Line Items] Divestitures [Line Items] [Line Items] for Divestitures [Table] Asset Retirement Obligation, Current Asset Retirement Obligation, Current ARO Liability [Roll Forward] Asset Retirement Obligation, Roll Forward Analysis [Roll Forward] ARO liability at January 1, Asset Retirement Obligation Accretion Asset Retirement Obligation, Accretion Expense Additions Asset Retirement Obligation, Liabilities Incurred Revisions Asset Retirement Obligation, Revision of Estimate Liabilities related to assets sold Asset Retirement Obligations, Liabilities Related to Divestitures Asset Retirement Obligations, Liabilities Related to Divestitures ARO liability at March 31, Debt Disclosure [Abstract] Schedule of Long-term Debt Instruments [Table] Schedule of Long-term Debt Instruments [Table] Long-term Debt, Type [Axis] Long-term Debt, Type [Axis] Long-term Debt, Type [Domain] Long-term Debt, Type [Domain] Revolving Credit Facility due 2019 [Member] Line of Credit [Member] 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. 5.375% Senior Notes Due 2022 [Member] Senior Notes Due 2022 [Member] Senior Notes Due 2022. 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 Long-term Debt, Weighted Average Interest Rate Long-term Debt, Weighted Average Interest Rate 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 Derivative Instrument [Axis] Derivative Instrument [Axis] Derivative Contract [Domain] Derivative Contract [Domain] Range [Axis] Range [Axis] Range [Domain] Range [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 Fair Value, Hierarchy [Axis] Fair Value, Hierarchy [Axis] Fair Value Hierarchy [Domain] Fair Value Hierarchy [Domain] Fair Value, Inputs, Level 2 [Member] Fair Value, Inputs, Level 2 [Member] Measurement Frequency [Axis] Measurement Frequency [Axis] Fair Value, Measurement Frequency [Domain] Fair Value, Measurement Frequency [Domain] Fair Value, Measurements, Recurring [Member] Fair Value, Measurements, Recurring [Member] Commodity Contract [Member] Commodity Contract [Member] Balance Sheet Location [Axis] Balance Sheet Location [Axis] Balance Sheet Location [Domain] Balance Sheet Location [Domain] Short-term [Member] Short term [Member] Derivative contracts with maturities of one year or less. Long-term [Member] Long term [Member] Derivative contracts with maturities in excess of one year. Derivative Asset, Fair Value, Gross Derivative Asset, Fair Value, Gross Asset Derivative Liability, Fair Value, Gross Derivative Liability, Fair Value, Gross Liability Earnings Per Share [Text Block] Earnings Per Share [Text Block] Pension Plan and SERP [Member] Pension Plan and SERP [Member] Pension Plan and SERP [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) Periodic expense Defined Benefit Plan, Net Periodic Benefit Cost Other Acquisitions [Abstract] Other Acquisitions [Abstract] Schedule of Business Acquisitions, by Acquisition [Table] Schedule of Business Acquisitions, by Acquisition [Table] Business Acquisition [Axis] Business Acquisition [Axis] Business Acquisition, Acquiree [Domain] Business Acquisition, Acquiree [Domain] 2017 Permian Basin Acquisition [Member] 2017 Permian Basin Acquisition [Member] 2017 Permian Basin Acquisition [Member] Permian Basin Acquisition [Member] Permian Basin Acquisition [Member] Permian Basin Acquisition [Member] Other Acquisitions [Member] Other Acquisitions [Member] Other Acquisitions [Member] Business Acquisition [Line Items] Business Acquisition [Line Items] Bargain purchase gain from acquisition Business Combination, Bargain Purchase, Gain Recognized, Amount Acquisition Costs, Period Cost Acquisition Costs, Period Cost Payments to acquire oil and gas property Payments to Acquire Oil and Gas Property Goodwill Goodwill Share-based Compensation Expense [Table] Share-based Compensation Expense [Table] Share-based Compensation Expense [Table] Award Type [Axis] Award Type [Axis] Equity Award [Domain] Equity Award [Domain] Stock Options [Member] Employee Stock Option [Member] Restricted Share Awards [Member] Restricted Stock [Member] Performance Share Units [Member] Performance Share Units [Member] Incremental common shares attributable to performance share units. Restricted Share Units (RSUs) [Member] Restricted Stock Units (RSUs) [Member] 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 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] Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Share-based Compensation Arrangement by Share-based Payment Award [Line Items] 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 forfeited Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested Options Forfeited, Number of Shares Options canceled Share-based Compensation Arrangement by Share-based Payment Award, Options, Other Increases (Decreases) in Period Outstanding at end of period Options exercisable, shares Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Number Unvested options, shares Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested, Number of Shares 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, forfeited in period Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures and Expirations 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, weighted average exercise price Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Exercise Price 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. Restricted Cash [Abstract] Restricted Cash [Abstract] Schedule of Restricted Cash and Cash Equivalents [Table Text Block] Schedule of Restricted Cash and Cash Equivalents [Table Text Block] Debt Outstanding [Table Text Block] Schedule of Debt [Table Text Block] Income Statement [Abstract] REVENUES Revenues [Abstract] Oil and condensate, gas and NGL sales Exploration and Production Revenue Other revenue Gas Gathering, Transportation, Marketing and Processing Revenue Purchased oil and gas sales Revenue from Purchased Oil and Gas Total Revenues Oil and Gas Revenue OPERATING EXPENSES Operating Expenses [Abstract] Purchased oil and gas expense Cost of Purchased Oil and Gas Lease operating expense Oil and Gas Property, Lease Operating Expense Transportation and processing costs Gas Gathering, Transportation, Marketing and Processing Costs Gathering and other expense Other Cost and Expense, Operating General and administrative General and Administrative Expense Production and property taxes Production Tax Expense Depreciation, depletion and amortization Depreciation, Depletion and Amortization Exploration expenses Exploration Expense Impairment Asset Impairment Charges Total Operating Expenses Operating Expenses Net gain (loss) from asset sales Gain (Loss) on Disposition of Oil and Gas Property OPERATING INCOME (LOSS) Operating Income (Loss) Realized and unrealized gains (losses) on derivative contracts (Note 7) Gain (Loss) on Derivative Instruments, Net, 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) Earnings (loss) per common share Basic Earnings Per Share, Basic Diluted Earnings Per Share, Diluted Weighted-average common shares outstanding Weighted Average Number of Shares Outstanding, Diluted [Abstract] Used in basic calculation Weighted Average Number of Shares Outstanding, Basic Used in diluted calculation Weighted Average Number of Shares Outstanding, Diluted Dividends per common share Common Stock, Dividends, Per Share, Cash Paid 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] Unvested balance at beginning of period Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number Shares granted Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period Shares vested Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period Shares forfeited Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period Unvested balance at end of period 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] 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 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 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 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 Weighted average grant date fair value, end of period Revenue Recognition [Text Block] Revenue Recognition [Text Block] Revenue Recognition [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 Restructuring and Related Activities Disclosure [Text Block] Restructuring and Related Activities Disclosure [Text Block] Statement of Cash Flows [Abstract] OPERATING ACTIVITIES Net Cash Provided by (Used in) Operating Activities [Abstract] Net income (loss) Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities: Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract] Deferred income taxes (benefit) Deferred Income Tax Expense (Benefit) Share-based compensation Share-based Compensation Amortization of debt issuance costs and discounts Amortization of Debt Issuance Costs and Discounts Bargain purchase gain from acquisition Net gain (loss) from asset sales 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 Property, plant and equipment, including 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 Proceeds from credit facility Proceeds from Long-term Lines of Credit Repayments of credit facility Repayments of Long-term Lines of Credit Common stock repurchased and retired Stock Repurchased and Retired During Period, Value Treasury stock repurchases Payments for Repurchase of Common Stock Net Cash Provided by (Used in) Financing Activities Net Cash Provided by (Used in) Financing Activities, Continuing Operations Change in cash, cash equivalents and restricted cash Cash and Cash Equivalents, Period Increase (Decrease) Beginning cash, cash equivalents and restricted cash(1) Restricted Cash and Cash Equivalents Ending cash, cash equivalents and restricted cash(1) Supplemental Disclosures: Supplemental Cash Flow Elements [Abstract] Cash paid for interest, net of capitalized interest Interest Paid, Net Cash paid for income taxes, net Income Taxes Paid, Net Non-cash Investing Activities: Noncash Investing and Financing Items [Abstract] Change in capital expenditure accruals and other non-cash adjustments Change in capital expenditure accruals and other non-cash adjustments Change in capital expenditure accruals and other non-cash adjustments Fair Value Disclosures [Abstract] Fair Value, by Balance Sheet Grouping [Table] Fair Value, by Balance Sheet Grouping [Table] Fair Value, Measurements, Fair Value Hierarchy [Domain] Level 1 [Member] Fair Value, Inputs, Level 1 [Member] Level 2 [Member] Level 3 [Member] Fair Value, Inputs, Level 3 [Member] Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] Financial Assets Derivative Asset [Abstract] Derivative Asset, Netting Adjustments Derivative Asset, Fair Value, Amount Offset Against Collateral Derivative Asset, Net Derivative Asset Financial liabilities Derivative Liability [Abstract] Derivative Liability, Netting Adjustments Derivative Liability, Fair Value, Amount Offset Against Collateral Derivative Liability, Net Derivative Liability Statement of Stockholders' Equity [Abstract] 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] Other Comprehensive Income (Loss) [Member] Other Comprehensive Income (Loss) [Member] Total [Member] Total [Member] Total [Member] Common Stock, Shares Shares, Issued Treasury Stock, Shares Treasury Stock, Shares Net income (loss), Shares Stockholders' Equity, Other Shares Net income (loss) Common stock repurchased and retired, Shares Stock Repurchased and Retired During Period, Shares Common stock repurchased and retired Share-based compensation, Shares Stock Issued During Period, Shares, Share-based Compensation, Net of Forfeitures Share-based compensation Stock Granted, Value, Share-based Compensation, Net of Forfeitures Stock Issued During Period, Shares, Treasury Stock Reissued Stock Issued During Period, Shares, Treasury Stock Reissued Share-based compensation Stock Issued During Period, Value, Share-based Compensation, Net of Forfeitures Stock Issued During Period, Shares, Employee Benefit Plan Stock Issued During Period, Shares, Employee Benefit Plan Change in pension and postretirement liability, net of tax Stockholders' Equity Fair Value Measurements, Recurring and Nonrecurring [Table] Fair Value Measurements, Recurring and Nonrecurring [Table] 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] 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] Impairment of Oil and Gas Properties Impairment of Oil and Gas Properties Pinedale Divestiture [Abstract] Pinedale Divestiture [Abstract] Oil and Gas Delivery Commitments and Contracts [Axis] Oil and Gas Delivery Commitments and Contracts [Axis] Oil and Gas Delivery Commitments and Contracts Oil and Gas Delivery Commitments and Contracts, Oil Producing Property [Domain] Proceeds from Sale of Oil and Gas Property and Equipment Net gain (loss) from asset sales Gain (Loss) on Disposition of Property Plant Equipment Income (loss) before income taxes Minimum volume commitment Long-term Purchase Commitment, Amount Minimum volume commitment remaining Purchase Commitment, Remaining Minimum Amount Committed Measurement Basis [Axis] Measurement Basis [Axis] Fair Value Measurement [Domain] Fair Value Measurement [Domain] Reported Value Measurement [Member] Reported Value Measurement [Member] Estimate of Fair Value Measurement [Member] Estimate of Fair Value Measurement [Member] Cash and Cash Equivalents, at Carrying Value Long-term debt Long-term Debt Long-term debt, fair value Long-term Debt, Fair Value Other Divestitures [Abstract] Other Divestitures [Abstract] Non-core properties Divestitures [Member] Non-core properties Divestitures [Member] Non-core properties Divestitures [Member] Employee Benefits [Text Block] Pension and Other Postretirement Benefits Disclosure [Text Block] 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) 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] Organization, Consolidation and Presentation of Financial Statements [Abstract] Basis of Presentation [Text Block] Nature of Operations [Text Block] Debt [Text Block] Debt Disclosure [Text Block] Fair Value Measurements [Text Block] Fair Value Disclosures [Text Block] Schedule of Restricted Share Unit Transactions [Abstract] Schedule of Restricted Share Unit Transactions [Abstract] 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] Restructuring Type [Axis] Restructuring Type [Axis] Type of Restructuring [Domain] Type of Restructuring [Domain] Restructuring Cost and Reserve [Line Items] Restructuring Cost and Reserve [Line Items] Special Termination Benefits Special Termination Benefits Special Termination Benefits Severance Costs Severance Costs Accelerated Share Based Compensation Accelerated Share Based Compensation Accelerated Share Based Compensation Employee Retention Bonus Cost Employee Retention Bonus Cost Employee Retention Bonus Cost Restructuring and Related Cost, Expected Cost Restructuring and Related Cost, Expected Cost NGL derivative contracts [Member] NGL derivative contracts [Member] NGL derivative contract [Member] 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. 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] 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 5.25% Senior Notes Due 2023 [Member] 5.25% Senior Notes Due 2023 [Member] 5.25% Senior Notes Due 2023 [Member] 5.625% Senior Notes Due 2026 [Member] 5.625% Senior Notes Due 2026 [Member] 5.625% Senior Notes Due 2026 [Member] Less unamortized discount Debt Instrument, Unamortized Discount Total long-term debt outstanding Less: current portion of long-term debt Long-term Debt, Current Maturities Cash and Cash Equivalents [Abstract] Schedule of Restricted Cash and Cash Equivalents [Table] Schedule of Restricted Cash and Cash Equivalents [Table] Restricted Cash and Cash Equivalents [Axis] Restricted Cash and Cash Equivalents [Axis] Cash and Cash Equivalents [Domain] Cash and Cash Equivalents [Domain] Restricted Cash and Cash Equivalents Items [Line Items] Restricted Cash and Cash Equivalents Items [Line Items] Restricted cash(1) Restricted Cash and Investments Total cash, cash equivalents and restricted cash shown in the Condensed Consolidated Statements of Cash Flows Schedule of Net Benefit Costs [Table Text Block] Schedule of Net Benefit Costs [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 Operating Activities [Axis] Operating Activities [Axis] Operating Activities [Domain] Operating Activities [Domain] Shares available for future grants Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant Unrecognized compensation costs Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized Weighted average vesting period 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 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 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, PSUs & RSUs [Table Text Block] Schedule of Other Share-based Compensation, Activity [Table Text Block] Disaggregated Revenue [Abstract] Disaggregated Revenue [Abstract] Adjustments for New Accounting Pronouncements [Axis] Adjustments for New Accounting Pronouncements [Axis] Type of Adoption [Domain] Type of Adoption [Domain] As reported [Member] As reported [Member] As reported [Member] Revenues as reported [Member] Revenues as reported [Member] Revenues as reported [Member] Geographical [Axis] Geographical [Axis] Geographical [Domain] Geographical [Domain] Williston Basin [Member] Williston Basin [Member] Williston Basin [Member] Pinedale [Member] Pinedale [Member] Pinedale [Member] Uinta Basin [Member] Uinta Basin [Member] Uinta Basin [Member] Other Northern [Member] Other Northern [Member] Other Northern [Member] Permian Basin [Member] Permian Basin [Member] Permian Basin [Member] Haynesville/Cotton Valley [Member] Haynesville [Member] Haynesville [Member] Other Southern [Member] Other Southern [Member] Other Southern [Member] Oil and condensate sales Oil and Condensate Revenue Gas sales Natural Gas Production Revenue NGL sales Natural Gas Midstream Revenue Revenue Recognition [Table] Revenue Recognition [Table] Revenues as Adjusted [Member] Revenues as Adjusted [Member] Revenues as adjusted [Member] Adjustments for New Accounting Pronouncement [Member] Adjustments for New Accounting Pronouncement [Member] Income Statement, as adjusted [Member] Income Statement, as adjusted [Member] Income Statement, as adjusted [Member] Revenue Recognition [Line Items] Revenue Recognition [Line Items] [Line Items] for Revenue Recognition [Table] Other revenue Purchased oil and gas sales OPERATING EXPENSES Lease operating expense General and administrative Production and property taxes Exploration expenses Impairment OPERATING INCOME (LOSS) Realized and unrealized gains (losses) on derivative contracts (Note 7) Interest expense INCOME (LOSS) BEFORE INCOME TAXES Used in basic calculation