CONSOLIDATED BALANCE SHEETS Parenthetical - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Oil and Gas Property, Successful Effort Method, Accumulated Depreciation, Depletion and Amortization	$ 3,481,836	$ 3,233,012
Property, Plant and Equipment, Other, Accumulated Depreciation	$ 32,956	$ 37,079
Common Stock, Par Value Per Share	$ 0.01	$ 0.01
Common Stock, Shares Authorized	200,000,000	200,000,000
Common Stock, Shares, Issued	68,075,700	67,463,060
Common Stock, Shares, Outstanding	68,075,700	67,463,060
Assets Held-for-sale [Member]
Oil and Gas Property, Successful Effort Method, Accumulated Depreciation, Depletion and Amortization	$ 0	$ 22,482