Provision (Benefit) for Income Taxes (Details 2) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
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%	$ 12,803	$ 47,282	$ 26,008
State tax provisions (benefits), net of federal benefits	(110)	1,505	641
Cumulative impact of adjustments to net state income tax rate	(854)	(2,663)	(1,718)
Valuation allowance of carryover tax assets	2,070	2,273	1,681
Non-deductible equity compensation	1,911	1,537	867
Liability for Uncertain Tax Positions, Noncurrent	(977)	0	0
Other, net	796	560	354
Income tax provision	$ 15,639	$ 50,494	$ 27,833
Effective rate	42.80%	37.40%	37.50%