Provision (Benefit) for Income Taxes (Details 3) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Deferred tax assets:
Federal net operating losses ("NOLs")	$ 54,954	$ 30,715	$ 28,200
NOLs for excess stock-based compensation	(9,450)	(7,590)	6,900
Alternative minimum tax credits	3,451	2,092
Carryover items, net of valuation allowance	8,617	8,823
Unrealized stock compensation	7,151	5,519
Other	7,580	7,026
Total deferred tax assets	72,303	46,585
Deferred tax liabilities:
Oil and gas exploration and development costs	(270,158)	(195,454)
Other	(2,109)	(2,349)
Total deferred tax liabilities	(272,267)	(197,803)
Net deferred tax liabilities	(199,964)	(151,218)
Net current deferred tax assets	6,603	6,347
Net non-current deferred tax liabilities	$ 206,567	$ 157,565