Oil and Natural Gas Properties (Details) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended
	Jun. 30, 2015	Mar. 31, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Property, Plant and Equipment [Line Items]
Impairment of long-lived assets	$ 0	$ 272,000	$ 0	$ 272,000	$ 0
Oil and natural gas:
Proved properties	4,128,644			4,128,644		$ 4,025,595
Unproved properties	839,078			839,078		846,464
Oil and natural gas properties (successful efforts method)	4,967,722			4,967,722		4,872,059
Less accumulated depletion and amortization	(923,731)			(923,731)		(525,007)
Oil and natural gas properties, successful efforts method, net	$ 4,043,991			$ 4,043,991		$ 4,347,052
California operating area [Member]
Property, Plant and Equipment [Line Items]
Impairment of long-lived assets		207,000
East Texas operating area [Member]
Property, Plant and Equipment [Line Items]
Impairment of long-lived assets		$ 65,000