Fair Value Measurements (Details 2) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2015		Dec. 31, 2014		Dec. 31, 2013
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Period of New York Mercantile Exchange Strip Pricing Used for Price Forecast		5 years
Proved Oil and Gas Properties
Period of New York Mercantile Exchange Strip Pricing Used for Price Forecast		5 years
Impairment of proved properties		$ 468,679		$ 84,480		$ 172,641
Proved Oil and Gas Property, Successful Effort Method		7,606,405		7,348,436
Unproved Oil and Gas Property, Successful Effort Method		284,538		532,498
Impairment of other property and equipment		49,369		0		0
Property, Plant and Equipment, Other, Net		153,100		334,356
Disposal Group, Not Discontinued Operation, Loss (Gain) on Write-down		98,600		27,600
Oil and gas properties held for sale		$ 641		$ 17,891
Net Profit Plan liability [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value Inputs, Discount Rate		10.00%		12.00%
Period of New York Mercantile Exchange Strip Pricing Used for Price Forecast		5 years
Period Used for Price Assumptions of Strip Prices of Liabilities		1 year
Percentage change in commodity prices (as a percent)		5.00%
Change in liability due to change in commodity prices by 5 percent		$ 1,100
Percent Change in Discount Rate for Sensitivity Analysis		1.00%
Sensitivity Analysis Change in Liability Due to Change in Discount Rate		$ 300
Fair Value, NPP Reconciliation, Calculation [Roll Forward]
Net Profits Plan Liability: Beginning Balance		27,136		$ 56,985		78,827
Net increase (decrease) in liability	[1]	(12,238)		(12,492)		3,527
Net settlements	[1],[2]	(7,287)		(17,357)		(25,369)
Transfers in (out) of Level 3		0		0		0
Net Profits Plan Liability: Ending balance		7,611		27,136		56,985
Cash Payments Made or Accrued under Profit Sharing Plan Related to Divested Property		$ 3,800		8,300		$ 10,300
Proved Oil and Gas Properties
Period of New York Mercantile Exchange Strip Pricing Used for Price Forecast		5 years
6.625% Senior Notes Due 2019 [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Long-term Debt, Fair Value	[3]	$ 0		350,018
6.50% Senior Notes Due 2021 [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Long-term Debt, Fair Value		262,938		343,000
6.125% Senior Notes Due 2022 [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Long-term Debt, Fair Value		440,250		556,500
6.50% Senior Notes Due 2023 [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Long-term Debt, Fair Value		296,000		379,000
5% Senior Notes Due 2024 [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Long-term Debt, Fair Value		334,065		435,000
5.625% Senior Notes Due 2025 [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Long-term Debt, Fair Value	[3]	326,875		$ 0
Oil and Gas Properties [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value Inputs, Discount Rate				12.00%
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Nonrecurring [Member]
Proved Oil and Gas Properties
Proved Oil and Gas Property, Successful Effort Method		124,184	[4]	$ 33,423	[5]
Unproved Oil and Gas Property, Successful Effort Method	[4]	0		0
Property, Plant and Equipment, Other, Net	[5]	$ 629
Oil and gas properties held for sale	[5]			$ 17,891
Minimum [Member] | Oil and Gas Properties [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value Inputs, Discount Rate		10.00%
Maximum [Member] | Oil and Gas Properties [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value Inputs, Discount Rate		15.00%

[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. The amounts in the table include cash payments made or accrued under the Net Profits Plan of $3.8 million, $8.3 million, and $10.3 million for the years ended December 31, 2015, 2014, and 2013, respectively, as a result of the divestitures of properties subject to the Net Profits Plan.

[3] The 2019 Notes were fully redeemed on June 22, 2015 and the 2025 Notes were issued on May 21, 2015.

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

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