Reconciliation of Effective Tax Rate to Federal Statutory Tax Rate (Detail)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
U.S. federal statutory rate	35.00%	35.00%	35.00%
State taxes, net of federal benefit	2.60%	2.40%	2.90%
State incentives	(0.20%)	(0.50%)	(0.80%)
State law changes	0.30%	(0.90%)	(0.90%)
Nondeductible expenses	0.70%	0.40%	0.90%
Other			(0.10%)
Net effective rate	38.40%	36.40%	37.00%