Guarantor Financial Statements (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008
Current assets:
Cash and cash equivalents	$ 38,451	$ 106,956	$ 69,293	$ 68,137
Restricted cash	0	5,500
Accounts receivable	118,139	88,529
Fair value of hedging contracts	25,177	12,955
Current income tax receivable	19,946	0
Deferred taxes	26,072	27,274
Inventory	4,643	6,465
Other current assets	791	768
Total current assets	233,219	248,447
Oil and gas properties full cost method proved, net	1,473,439	984,629
Unevaluated	401,609	413,180
Other property and equipment, net of accumulated depreciation of $24263, and $22,467, respectively	11,172	10,722
Fair value of hedging contracts	22,543	0
Other assets, net	23,769	22,112
Investment in subsidiary	0	0
Total assets	2,165,751	1,679,090
Current liabilities:
Accounts payable to vendors	102,946	103,208
Undistributed oil and gas proceeds	27,328	10,037
Accrued interest	14,059	14,062
Fair value of hedging contracts	11,122	32,144
Asset retirement obligations	62,676	42,300
Current income tax payable	0	239
Other current liabilities	28,370	16,075
Total current liabilities	246,501	218,065
Long-term debt	620,000	575,000
Deferred taxes	247,835	99,227
Asset retirement obligations	363,103	331,620
Fair value of hedging contracts	815	3,606
Other long-term liabilities	19,668	21,215
Total liabilities	1,497,922	1,248,733
Commitments and contingencies
Stockholders' equity:
Common stock	481	478
Treasury stock (16,582 shares, respectively, at cost)	(860)	(860)
Additional paid-in capital	1,338,565	1,331,500
Accumulated earnings (deficit)	(692,225)	(886,557)
Accumulated other comprehensive income (loss)	21,868	(14,204)
Total stockholders' equity	667,829	430,357
Total liabilities and stockholders' equity	2,165,751	1,679,090
Parent [Member]
Current assets:
Cash and cash equivalents	37,389	105,115	64,830	67,122
Restricted cash		5,500
Accounts receivable	36,463	26,760
Fair value of hedging contracts	0	12,955
Current income tax receivable	19,946
Deferred taxes	8,269	27,274
Inventory	4,360	6,168
Other current assets	791	753
Total current assets	107,218	184,525
Oil and gas properties full cost method proved, net	387,554	260,434
Unevaluated	246,269	337,725
Other property and equipment, net of accumulated depreciation of $24263, and $22,467, respectively	11,172	10,722
Fair value of hedging contracts	0
Other assets, net	20,873	22,112
Investment in subsidiary	733,533	427,273
Total assets	1,506,619	1,242,791
Current liabilities:
Accounts payable to vendors	78,170	60,019
Undistributed oil and gas proceeds	26,036	9,491
Accrued interest	14,059	14,062
Fair value of hedging contracts	0	32,144
Asset retirement obligations	0	0
Current income tax payable		239
Other current liabilities	22,974	16,075
Total current liabilities	141,239	132,030
Long-term debt	620,000	575,000
Deferred taxes	56,970	(41,804)
Asset retirement obligations	7,626	129,100
Fair value of hedging contracts	0	3,606
Other long-term liabilities	12,955	14,502
Total liabilities	838,790	812,434
Commitments and contingencies
Stockholders' equity:
Common stock	481	478
Treasury stock (16,582 shares, respectively, at cost)	(860)	(860)
Additional paid-in capital	1,338,565	1,331,500
Accumulated earnings (deficit)	(692,225)	(886,557)
Accumulated other comprehensive income (loss)	21,868	(14,204)
Total stockholders' equity	667,829	430,357
Total liabilities and stockholders' equity	1,506,619	1,242,791
Guarantor Subsidiary [Member]
Current assets:
Cash and cash equivalents	926	1,659	3,963	818
Restricted cash		0
Accounts receivable	81,452	61,560
Fair value of hedging contracts	25,177	0
Current income tax receivable	0
Deferred taxes	17,803	0
Inventory	283	297
Other current assets	0	15
Total current assets	125,641	63,531
Oil and gas properties full cost method proved, net	1,083,192	720,309
Unevaluated	155,340	75,455
Other property and equipment, net of accumulated depreciation of $24263, and $22,467, respectively	0	0
Fair value of hedging contracts	22,543
Other assets, net	2,896	0
Investment in subsidiary	(273)	1,561
Total assets	1,389,339	860,856
Current liabilities:
Accounts payable to vendors	25,866	43,881
Undistributed oil and gas proceeds	1,292	546
Accrued interest	0	0
Fair value of hedging contracts	11,122	0
Asset retirement obligations	62,676	42,300
Current income tax payable		0
Other current liabilities	5,396	0
Total current liabilities	106,352	86,727
Long-term debt	0	0
Deferred taxes	190,865	141,031
Asset retirement obligations	351,061	198,105
Fair value of hedging contracts	815	0
Other long-term liabilities	6,713	6,713
Total liabilities	655,806	432,576
Commitments and contingencies
Stockholders' equity:
Common stock	0	0
Treasury stock (16,582 shares, respectively, at cost)	0	0
Additional paid-in capital	1,724,232	1,673,598
Accumulated earnings (deficit)	(1,012,567)	(1,245,318)
Accumulated other comprehensive income (loss)	21,868	0
Total stockholders' equity	733,533	428,280
Total liabilities and stockholders' equity	1,389,339	860,856
Non-Guarantor Subsidiaries [Member]
Current assets:
Cash and cash equivalents	136	182	500	197
Restricted cash		0
Accounts receivable	1,353	902
Fair value of hedging contracts	0	0
Current income tax receivable	0
Deferred taxes	0	0
Inventory	0	0
Other current assets	0	0
Total current assets	1,489	1,084
Oil and gas properties full cost method proved, net	2,693	3,886
Unevaluated	0	0
Other property and equipment, net of accumulated depreciation of $24263, and $22,467, respectively	0	0
Fair value of hedging contracts	0
Other assets, net	0	0
Investment in subsidiary	0	0
Total assets	4,182	4,970
Current liabilities:
Accounts payable to vendors	39	0
Undistributed oil and gas proceeds	0	0
Accrued interest	0	0
Fair value of hedging contracts	0	0
Asset retirement obligations	0	0
Current income tax payable		0
Other current liabilities	0	0
Total current liabilities	39	0
Long-term debt	0	0
Deferred taxes	0	0
Asset retirement obligations	4,416	4,415
Fair value of hedging contracts	0	0
Other long-term liabilities	0	0
Total liabilities	4,455	4,415
Commitments and contingencies
Stockholders' equity:
Common stock	0	0
Treasury stock (16,582 shares, respectively, at cost)	0	0
Additional paid-in capital	1,639	1,640
Accumulated earnings (deficit)	(1,912)	(1,085)
Accumulated other comprehensive income (loss)	0	0
Total stockholders' equity	(273)	555
Total liabilities and stockholders' equity	4,182	4,970
Eliminations [Member]
Current assets:
Cash and cash equivalents	0	0
Restricted cash		0
Accounts receivable	(1,129)	(693)
Fair value of hedging contracts	0	0
Current income tax receivable	0
Deferred taxes	0	0
Inventory	0	0
Other current assets	0	0
Total current assets	(1,129)	(693)
Oil and gas properties full cost method proved, net	0	0
Unevaluated	0	0
Other property and equipment, net of accumulated depreciation of $24263, and $22,467, respectively	0	0
Fair value of hedging contracts	0
Other assets, net	0	0
Investment in subsidiary	(733,260)	(428,834)
Total assets	(734,389)	(429,527)
Current liabilities:
Accounts payable to vendors	(1,129)	(692)
Undistributed oil and gas proceeds	0	0
Accrued interest	0	0
Fair value of hedging contracts	0	0
Asset retirement obligations	0	0
Current income tax payable		0
Other current liabilities	0	0
Total current liabilities	(1,129)	(692)
Long-term debt	0	0
Deferred taxes	0	0
Asset retirement obligations	0	0
Fair value of hedging contracts	0	0
Other long-term liabilities	0	0
Total liabilities	(1,129)	(692)
Commitments and contingencies
Stockholders' equity:
Common stock	0	0
Treasury stock (16,582 shares, respectively, at cost)	0	0
Additional paid-in capital	(1,725,871)	(1,675,238)
Accumulated earnings (deficit)	1,014,479	1,246,403
Accumulated other comprehensive income (loss)	(21,868)	0
Total stockholders' equity	(733,260)	(428,835)
Total liabilities and stockholders' equity	$ (734,389)	$ (429,527)