Condensed Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Current assets:
Cash and cash equivalents	$ 3,885	$ 1,521
Restricted cash	51,757
Trade accounts receivable - net	75,421	67,991
Fair value of commodity derivative instruments	10,758	3,302
Deferred tax asset		3,322
Prepaid expenses	15,730	9,873
Total current assets	157,551	86,009
Property and equipment, at cost under the successful efforts method of accounting	2,152,483	2,025,647
Less accumulated depreciation, depletion, amortization and impairments	(515,136)	(427,580)
Net property and equipment	1,637,347	1,598,067
Restricted cash	6,023	6,023
Fair value of commodity derivative instruments	7,600	211
Deferred financing costs -- net of accumulated amortization of $4,055 at March 31, 2013 and $2,596 at December 31, 2012	11,564	12,386
Other assets	2,660	2,931
Total Assets	1,822,745	1,705,627
Current liabilities:
Accounts payable	32,985	34,772
Accrued expenses	135,800	117,372
Asset retirement obligations	28,162	30,179
Fair value of commodity derivative instruments	1,208	10,026
Deferred tax liabilities	2,601
Total current liabilities	200,756	192,349
Long-term debt	661,106	689,911
Asset retirement obligations	199,005	204,931
Deferred tax liabilities	118,062	67,694
Fair value of commodity derivative instruments		3,637
Other	1,191	1,132
Total Liabilities	1,180,120	1,159,654
Commitments and contingencies
Stockholders' equity:
Preferred stock, $0.001 par value. Authorized 1,000,000 shares; no shares issued and outstanding at June 30, 2013 and December 31, 2012
Common stock, par value $0.001 per share. Authorized 75,000,000 shares; shares issued: 40,912,718 and 40,601,887 at June 30, 2013 and December 31, 2012, respectively; shares outstanding: 39,202,605 and 39,103,203 at June 30, 2013 and December 31, 2012, respectively	40	40
Additional paid-in capital	514,410	510,469
Treasury stock, at cost, 1,710,113 and 1,498,684 shares at June 30, 2013 and December 31, 2012, respectively	(26,382)	(20,477)
Retained earnings	154,557	55,941
Total stockholders' equity	642,625	545,973
Total liabilities and stockholders' equity	$ 1,822,745	$ 1,705,627