Statutory Federal Income Tax Rate and the Effective Income Tax Rate Reconciliation (Detail)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Reconciliation of Statutory Federal Tax Rate [Line Items]
Statutory federal income tax rate	35.00%	35.00%	35.00%
State income taxes	4.40%	4.30%	5.70%
Book gain on acquisition of business			(4.50%)
Uncertain tax positions	0.40%	(0.30%)	0.10%
Federal and state tax credits	(1.70%)	(3.10%)
Nondeductible expenses	2.00%	1.40%	0.80%
Other	0.30%	0.20%	(0.30%)
Effective federal and state income tax rate	40.40%	37.50%	36.80%