Property and Equipment (Details) $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2014 $ / bbl	Sep. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)	Sep. 30, 2015 USD ($) $ / bbl	Sep. 30, 2014 USD ($)	Dec. 31, 2014 USD ($)
Oil and natural gas properties:
Subject to depletion		$ 2,750,460		$ 2,750,460		$ 2,345,077
Not subject to depletion-acquisition costs		1,099,604		1,099,604		773,520
Gross oil and natural gas properties		3,850,064		3,850,064		3,118,597
Accumulated depletion		(870,569)		(870,569)		(379,481)
Impairment		(273,737)	$ 0	(597,188)	$ 0	0
Oil and natural gas properties, net		2,705,758		2,705,758		2,739,116
Pipeline and gas gathering assets		7,176		7,176		7,174
Other property and equipment		48,913		48,913		48,180
Accumulated depreciation		(1,147,936)		(1,147,936)		(382,144)
Property and equipment, net of accumulated depreciation, depletion, amortization and impairment		2,758,217		2,758,217		2,791,807
Capitalized general and administrative costs		4,000	$ 2,400	12,100	$ 7,300
Price of oil and gas (in dollars per bbl) | $ / bbl	91.00
Incurred in 2015 [Member]
Oil and natural gas properties:
Not subject to depletion-acquisition costs		421,576		421,576		0
Incurred in 2014 [Member]
Oil and natural gas properties:
Not subject to depletion-acquisition costs		543,499		543,499		576,802
Incurred in 2013 [Member]
Oil and natural gas properties:
Not subject to depletion-acquisition costs		71,802		71,802		130,474
Incurred in 2012 [Member]
Oil and natural gas properties:
Not subject to depletion-acquisition costs		62,727		62,727		65,480
Incurred in 2011 [Member]
Oil and natural gas properties:
Not subject to depletion-acquisition costs		0		$ 0		764
Minimum [Member]
Oil and natural gas properties:
Number of years until unevaluated properties are included in full cost pool				3 years
Price of oil and gas (in dollars per bbl) | $ / bbl				38
Maximum [Member]
Oil and natural gas properties:
Number of years until unevaluated properties are included in full cost pool				5 years
Price of oil and gas (in dollars per bbl) | $ / bbl				62
Other Property and Equipment, Net [Member]
Oil and natural gas properties:
Accumulated depreciation		$ (3,630)		$ (3,630)		$ (2,663)