Property and Equipment (Schedule Of Property And Equipment) (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Oil and Gas Property, Full Cost Method, Net [Abstract]
Oil and gas properties under the full cost method	$ 1,380,273	$ 1,265,234
Computers, furniture and fixtures	8,733	8,863
Total property and equipment	1,389,006	1,274,097
Accumulated depreciation, depletion and amortization	(334,172)	(270,656)
Net property and equipment	1,054,834	1,003,441
Subject To Amortization [Member]
Oil and Gas Property, Full Cost Method, Net [Abstract]
Oil and gas properties under the full cost method	996,270	915,801
Not Subject To Amortization [Member] | Incurred in 2013
Oil and Gas Property, Full Cost Method, Net [Abstract]
Oil and gas properties under the full cost method	52,508
Not Subject To Amortization [Member] | Incurred in 2012
Oil and Gas Property, Full Cost Method, Net [Abstract]
Oil and gas properties under the full cost method	144,865	141,837
Not Subject To Amortization [Member] | Incurred in 2011
Oil and Gas Property, Full Cost Method, Net [Abstract]
Oil and gas properties under the full cost method	99,971	107,510
Not Subject To Amortization [Member] | Incurred prior to 2011
Oil and Gas Property, Full Cost Method, Net [Abstract]
Oil and gas properties under the full cost method	$ 86,659	$ 100,086