Condensed Consolidated Balance Sheet (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011	Jun. 30, 2011	Dec. 31, 2010
Current assets:
Cash and cash equivalents	$ 223,849	$ 38,451	$ 82,021	$ 106,956
Accounts receivable	148,934	118,139
Fair value of hedging contracts	61,203	25,177
Current income tax receivable	24,353	19,946
Deferred taxes	7,474	26,072
Inventory	4,607	4,643
Other current assets	914	791
Total current assets	471,334	233,219
Oil and gas properties, full cost method of accounting:
Proved	6,927,917	6,648,168
Less: accumulated depreciation, depletion and amortization	(5,339,251)	(5,174,729)
Net proved oil and gas properties	1,588,666	1,473,439
Unevaluated	435,384	401,609
Other property and equipment, net	11,910	11,172
Fair value of hedging contracts	41,981	22,543
Other assets, net	33,955	23,769
Total assets	2,583,230	2,165,751
Current liabilities:
Accounts payable to vendors	143,389	102,946
Undistributed oil and gas proceeds	27,248	27,328
Accrued interest	15,735	14,059
Fair value of hedging contracts		11,122
Asset retirement obligations	75,493	62,676
Other current liabilities	9,470	28,370
Total current liabilities	271,335	246,501
Long-term debt	808,050	620,000
Deferred taxes	298,551	247,835
Asset retirement obligations	351,785	363,103
Fair value of hedging contracts	366	815
Other long-term liabilities	20,651	19,668
Total liabilities	1,750,738	1,497,922
Commitments and contingencies
Stockholders' equity:
Common stock, $.01 par value; authorized 100,000,000 shares; issued 48,331,956 and 48,076,860 shares, respectively	483	481
Treasury stock (16,582 shares, at cost)	(860)	(860)
Additional paid-in capital	1,380,568	1,338,565
Accumulated deficit	(610,704)	(692,225)
Accumulated other comprehensive income	63,005	21,868
Total stockholders' equity	832,492	667,829
Total liabilities and stockholders' equity	$ 2,583,230	$ 2,165,751