Provision (Benefit) for Income Taxes (Details 2) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Reconciliations of income taxes computed using the U.S. Federal statutory rate to the effective income tax rates
Income taxes (or benefits) computed at U.S. statutory rate -35%	$ 47,282	$ 26,008	$ (22,616)
State tax provisions (benefits), net of federal benefits	1,505	641	(1,956)
Cumulative impact of adjustments to net state income tax rate	(2,663)	(1,718)
Valuation allowance of carryover tax assets	2,273	1,681	(1,082)
Non-deductible equity compensation	1,537	867	105
Other, net	560	354	8
Provision (benefit) for income taxes	$ 50,494	$ 27,833	$ (25,541)
Effective rate	37.40%	37.50%	39.50%