Fair Value Measurements (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014	May. 13, 2014	May. 28, 2013
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis [Abstract]
Impairment	$ 1,398,183		$ 1,398,183		$ 1,639,974
Impairment of long-lived assets			209,400
Long-term debt, gross	985,000		985,000		959,000
Credit facility due 2019
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis [Abstract]
Long-term debt, gross	135,000		135,000		109,000
Senior notes | 8% Senior Notes due 2020
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis [Abstract]
Long-term debt, gross	300,000		300,000		300,000
Senior notes | 6.625% Senior Notes due 2021
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis [Abstract]
Long-term debt, gross	550,000		550,000		$ 550,000	$ 300,000	$ 250,000
Quoted Prices in Active Markets for Identical Assets (Level 1) | Senior notes | 8% Senior Notes due 2020
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis [Abstract]
Fair value of notes payable	260,700		260,700
Quoted Prices in Active Markets for Identical Assets (Level 1) | Senior notes | 6.625% Senior Notes due 2021
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis [Abstract]
Fair value of notes payable	440,000		440,000
Recurring
Schedule of financial assets and liabilities that were accounted for at fair value on a recurring basis
LTIP liability	(28)		(28)
Fair value of assets (liabilities)	81,543		81,543
Recurring | Commodity derivatives | Oil and natural gas
Schedule of financial assets and liabilities that were accounted for at fair value on a recurring basis
Derivative asset	82,556		82,556
Recurring | Interest rate swaps
Schedule of financial assets and liabilities that were accounted for at fair value on a recurring basis
Derivative liability	(985)		(985)
Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Schedule of financial assets and liabilities that were accounted for at fair value on a recurring basis
LTIP liability	0		0
Fair value of assets (liabilities)	0		0
Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Commodity derivatives | Oil and natural gas
Schedule of financial assets and liabilities that were accounted for at fair value on a recurring basis
Derivative asset	0		0
Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Interest rate swaps
Schedule of financial assets and liabilities that were accounted for at fair value on a recurring basis
Derivative liability	0		0
Recurring | Significant Other Observable Inputs (Level 2)
Schedule of financial assets and liabilities that were accounted for at fair value on a recurring basis
LTIP liability	(28)		(28)
Fair value of assets (liabilities)	86,354		86,354
Recurring | Significant Other Observable Inputs (Level 2) | Commodity derivatives | Oil and natural gas
Schedule of financial assets and liabilities that were accounted for at fair value on a recurring basis
Derivative asset	87,367		87,367
Recurring | Significant Other Observable Inputs (Level 2) | Interest rate swaps
Schedule of financial assets and liabilities that were accounted for at fair value on a recurring basis
Derivative liability	(985)		(985)
Recurring | Significant Unobservable Inputs (Level 3)
Schedule of financial assets and liabilities that were accounted for at fair value on a recurring basis
LTIP liability	0		0
Fair value of assets (liabilities)	(4,811)		(4,811)
Reconciliation of changes in the fair value of financial assets and liabilities classified as Level 3
Beginning balance	(2,485)	$ 14,552	555	$ 20,615
Transfers	0	(14,552)	0	(14,552)
Total losses	(3,275)	0	(6,632)	(6,740)
Settlements, net	949	0	1,266	677
Ending balance	(4,811)	0	(4,811)	0
Losses included in earnings relating to derivatives still held as of June 30, 2015 and 2014			(4,811)	$ 0
Recurring | Significant Unobservable Inputs (Level 3) | Derivative assets
Reconciliation of changes in the fair value of financial assets and liabilities classified as Level 3
Losses included in earnings relating to derivatives still held as of June 30, 2015 and 2014	(3,492)	$ 0
Recurring | Significant Unobservable Inputs (Level 3) | Commodity derivatives | Oil and natural gas
Schedule of financial assets and liabilities that were accounted for at fair value on a recurring basis
Derivative asset	(4,811)		(4,811)
Recurring | Significant Unobservable Inputs (Level 3) | Interest rate swaps
Schedule of financial assets and liabilities that were accounted for at fair value on a recurring basis
Derivative liability	0		0
Nonrecurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis [Abstract]
Impairment	0		0
Acquisitions			0
Nonrecurring | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis [Abstract]
Impairment	0		0
Acquisitions			0
Nonrecurring | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis [Abstract]
Impairment	198,095		198,095
Acquisitions			1,923
Oil and gas properties, gross	$ 407,500		$ 407,500