Components of Provision Benefit 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 (benefit)
Federal									$ (5,782)	$ 3	$ 5,887
State									(440)	280	205
Deferred provision (benefit)
Federal									13,143	9,897	568
State									(587)	176	161
Provision for income taxes	$ 54	$ 1,333	$ 2,222	$ 2,725	$ 2,212	$ 2,774	$ 2,975	$ 2,395	$ 6,334	$ 10,356	$ 6,821