Fair Value Measurements Fair Value Measurement (Details 2) (USD $)	3 Months Ended
	Mar. 31, 2015 A		Mar. 31, 2014	Dec. 31, 2014
Liabiliity measured at fair value using Level 3 inputs
Derivative Asset, Fair Value, Gross Asset	$ 585,474,000			$ 592,208,000
Net Profits Plan
Number of Periods Used for Price Assumptions of Strip Prices of Liabilities	5
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Abstract]
Deferred Compensation Cash-based Arrangements, Liability, Classified, Noncurrent	27,136,000
Deferred Compensation Cash-based Arrangements, Liability, Classified, Noncurrent	22,802,000
Proved and Unproved Oil and Gas Properties
Discount Rate Used for Fair Value of Oil and Gas Properties				12.00%
Number of Periods Used for Price Assumptions of Strip Prices of Liabilities	5
Impairment of Oil and Gas Properties	55,526,000		0
Abandonment and impairment of unproved properties	11,627,000		2,801,000
Proved Oil and Gas Property, Successful Effort Method	7,006,832,000			7,348,436,000
Unproved Oil and Gas Property, Successful Effort Method	512,461,000			532,498,000
Net Profit Plan liability [Member]
Net Profits Plan
Discount Rate Used to Calculate Currently in Payout Liabilities	12.00%
Number of Periods Used for Price Assumptions of Strip Prices of Liabilities	5
Period Used for Price Assumptions of Strip Prices of Liabilities	1
Percent Change in Commodity Prices for Sensitivity Analysis	5.00%
Sensitivity Analysis Change in Liability, Due to Change in Commodity Prices	2,000,000
Percent Change in Discount Rate for Sensitivity Analysis	1.00%
Sensitivity Analysis Decrease in Liability Due to Change in Discount Rate	1,000,000
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Abstract]
Deferred Compensation Cash-based Arrangements, Liability, Classified, Noncurrent	27,136,000
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Period Increase (Decrease)	(3,035,000)	[1]
Net settlements	(1,299,000)	[1],[2]
Transfers in (out) of Level 3	0
Deferred Compensation Cash-based Arrangements, Liability, Classified, Noncurrent	22,802,000
Proved and Unproved Oil and Gas Properties
Number of Periods Used for Price Assumptions of Strip Prices of Liabilities	5
6.625% Senior Notes Due 2019 [Member]
Liabiliity measured at fair value using Level 3 inputs
Long-term Debt, Fair Value	359,730,000			350,018,000
6.50% Senior Notes Due 2021 [Member]
Liabiliity measured at fair value using Level 3 inputs
Long-term Debt, Fair Value	357,438,000			343,000,000
6.125% Senior Notes Due 2022 [Member]
Liabiliity measured at fair value using Level 3 inputs
Long-term Debt, Fair Value	601,878,000			556,500,000
6.50% Senior Notes Due 2023 [Member]
Liabiliity measured at fair value using Level 3 inputs
Long-term Debt, Fair Value	408,080,000			379,000,000
5.0% Senior Notes Due 2024 [Member]
Liabiliity measured at fair value using Level 3 inputs
Long-term Debt, Fair Value	472,500,000			435,000,000
Mid Continent Divestiture 2015 [Member]
Proved and Unproved Oil and Gas Properties
Disposal Group, Not Discontinued Operation, Gain (Loss) on Disposal	30,000,000
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Nonrecurring [Member]
Proved and Unproved Oil and Gas Properties
Proved Oil and Gas Property, Successful Effort Method	48,969,000	[3]		33,423,000	[4]
Unproved Oil and Gas Property, Successful Effort Method	$ 0			$ 0

[1] Net changes in the Company’s Net Profits Plan liability are shown in the Change in Net Profits Plan liability line item of the accompanying statements of operations

[2] Settlements represent cash payments made or accrued under the Net Profits Plan.

[3] This represents a non-financial asset or liability that is measured at fair value on a nonrecurring basis.

[4] This represents a non-financial asset that is measured at fair value on a nonrecurring basis.