Property and Equipment (Net Property) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Oil and Gas Property, Full Cost Method, Net [Abstract]
Furniture and Fixtures, Gross	$ 8,863	$ 6,421
Property, Plant and Equipment, Gross	1,274,097	761,422
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	(270,656)	(212,226)
Property, Plant and Equipment, Net	1,003,441	549,196
[UnProvedMember]
Oil and Gas Property, Full Cost Method, Net [Abstract]
Oil and Gas Property, Full Cost Method, Gross	915,801	496,667
[ProvedMember]
Oil and Gas Property, Full Cost Method, Net [Abstract]
Oil and Gas Property, Full Cost Method, Gross	1,265,234	755,001
[ProvedMember] | [CurrentYearMember]
Oil and Gas Property, Full Cost Method, Net [Abstract]
Oil and Gas Property, Full Cost Method, Gross	141,837	0
[ProvedMember] | [OneYearPriorMember]
Oil and Gas Property, Full Cost Method, Net [Abstract]
Oil and Gas Property, Full Cost Method, Gross	107,510	138,912
[ProvedMember] | [TwoYearPriorMember]
Oil and Gas Property, Full Cost Method, Net [Abstract]
Oil and Gas Property, Full Cost Method, Gross	47,148	47,208
[ProvedMember] | [ThreeYearsAndPriorMember]
Oil and Gas Property, Full Cost Method, Net [Abstract]
Oil and Gas Property, Full Cost Method, Gross	$ 52,938	$ 72,214