Components of Provision for Income Taxes (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Current provision:
Federal									$ 87,635	$ 86,220	$ 47,794
State									23,752	25,505	15,042
Deferred expense (benefit):
Federal									2,385	5,756	(1,157)
State									(503)	1,606	(277)
Income tax expense	$ (29,526)	$ (28,470)	$ (31,517)	$ (23,756)	$ (26,284)	$ (26,770)	$ (43,263)	$ (22,770)	$ 113,269	$ 119,087	$ 61,402