Property and Equipment (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Oil and natural gas properties
Evaluated (subject to amortization)	$ 1,090,656	$ 763,527
Unproved and unevaluated (not subject to amortization)
Incurred in 2013	82,628	0
Incurred in 2012	23,341	36,488
Incurred in 2011	10,982	24,138
Incurred in 2010 and prior	77,355	89,049
Total unproved and unevaluated	194,306	149,675
Total oil and natural gas properties	1,284,962	913,202
Accumulated depletion	(463,091)	(344,609)
Net oil and natural gas properties	821,871	568,593
Other property and equipment
Other property and equipment	29,910	27,258
Accumulated depreciation	(5,904)	(4,761)
Net other property and equipment	24,006	22,497
Net property and equipment	845,877	591,090
Computer equipment [Member]
Other property and equipment
Other property and equipment	1,044	834
Furniture [Member]
Other property and equipment
Other property and equipment	1,057	793
Software [Member]
Other property and equipment
Other property and equipment	1,456	1,355
Other equipment [Member]
Other property and equipment
Other property and equipment	252	196
Leasehold improvements [Member]
Other property and equipment
Other property and equipment	991	644
Support equipment and facilities [Member]
Other property and equipment
Other property and equipment	$ 25,110	$ 23,436