Supplemental Condensed Consolidating Financial Information (Supplemental Condensed Consolidating Balance Sheet) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Cash and cash equivalents	$ 8,812	$ 1,521	$ 80,128	$ 33,553
Trade accounts receivable - net	70,707	67,991
Fair value of commodity derivative instruments	501	3,302
Deferred tax asset	8,949	3,322
Prepaid expenses	6,868	9,873
Total current assets	95,837	86,009
Property and equipment	2,355,219	2,025,647
Less accumulated depreciation, depletion, amortization and impairments	(618,788)	(427,580)
Net property and equipment	1,736,431	1,598,067
Deposit for Nexen Acquisition	7,040
Restricted cash	6,023	6,023
Fair value of commodity derivative instruments	238	211
Deferred financing costs	10,106	12,386
Other assets	2,156	2,931
Total Assets	1,857,831	1,705,627
Accounts payable	59,431	34,772
Accrued expenses	131,125	117,372
Asset retirement obligations	51,601	30,179
Fair value of commodity derivative instruments	29,636	10,026
Total current liabilities	271,793	192,349
Long-term debt	627,355	689,911
Asset retirement obligations	203,849	204,931
Deferred tax liabilities	122,812	67,694
Fair value of commodity derivative instruments	2,136	3,637
Other	673	1,132
Total liabilities	1,228,618	1,159,654
Preferred stock
Common stock	41	40
Additional paid-in capital	519,114	510,469
Treasury stock, at cost	(31,157)	(20,477)
Retained earnings	141,215	55,941
Total stockholders' equity	629,213	545,973	491,045	473,116
Total liabilities and stockholders' equity	1,857,831	1,705,627
Parent Company [Member]
Cash and cash equivalents	8,812	1,521	80,128	33,553
Trade accounts receivable - net	70,520	66,994
Intercompany receivable	39,085	55,575
Fair value of commodity derivative instruments	501	3,302
Deferred tax asset	8,949	3,322
Prepaid expenses	6,868	9,873
Total current assets	134,735	140,587
Property and equipment	2,041,689	1,754,294
Less accumulated depreciation, depletion, amortization and impairments	(526,736)	(353,526)
Net property and equipment	1,514,953	1,400,768
Investment in affiliates	122,697	111,191
Deposit for Nexen Acquisition	7,040
Restricted cash	6,023	6,023
Fair value of commodity derivative instruments	238	211
Deferred financing costs	10,106	12,386
Other assets	2,067	2,841
Total Assets	1,797,859	1,674,007
Accounts payable	58,758	34,740
Accrued expenses	131,111	117,245
Asset retirement obligations	51,601	23,982
Fair value of commodity derivative instruments	29,636	10,026
Total current liabilities	271,106	185,993
Long-term debt	627,355	689,911
Asset retirement obligations	160,466	187,790
Deferred tax liabilities	106,910	59,571
Fair value of commodity derivative instruments	2,136	3,637
Other	673	1,132
Total liabilities	1,168,646	1,128,034
Common stock	41	40
Additional paid-in capital	519,114	510,469
Treasury stock, at cost	(31,157)	(20,477)
Retained earnings	141,215	55,941
Total stockholders' equity	629,213	545,973
Total liabilities and stockholders' equity	1,797,859	1,674,007
Guarantor Subsidiaries [Member]
Trade accounts receivable - net	187	997
Total current assets	187	997
Property and equipment	313,530	271,353
Less accumulated depreciation, depletion, amortization and impairments	(92,052)	(74,054)
Net property and equipment	221,478	197,299
Other assets	89	90
Total Assets	221,754	198,386
Accounts payable	673	32
Intercompany payable	39,085	55,575
Accrued expenses	14	127
Asset retirement obligations		6,197
Total current liabilities	39,772	61,931
Asset retirement obligations	43,383	17,141
Deferred tax liabilities	15,902	8,123
Total liabilities	99,057	87,195
Additional paid-in capital	85,479	85,479
Retained earnings	37,218	25,712
Total stockholders' equity	122,697	111,191
Total liabilities and stockholders' equity	221,754	198,386
Consolidation, Eliminations [Member]
Intercompany receivable	(39,085)	(55,575)
Total current assets	(39,085)	(55,575)
Investment in affiliates	(122,697)	(111,191)
Total Assets	(161,782)	(166,766)
Intercompany payable	(39,085)	(55,575)
Total current liabilities	(39,085)	(55,575)
Total liabilities	(39,085)	(55,575)
Additional paid-in capital	(85,479)	(85,479)
Retained earnings	(37,218)	(25,712)
Total stockholders' equity	(122,697)	(111,191)
Total liabilities and stockholders' equity	$ (161,782)	$ (166,766)