Income Taxes - Summary of components of provision (benefit) for income taxes (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Current provision:
Federal	$ 147,580	$ 91,415	$ 56,289
State	14,673	12,938	11,180
Foreign	1,109	1,007	1,059
Deferred provision (benefit):
Federal	5,027	70,599	22,833
State	(206)	6,475	(571)
Total income tax provision	$ 168,183	$ 182,434	$ 90,790