Income Taxes Reconciliation between Federal Statutory Income Tax Rate and Effective Income Tax Rate (Detail)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Tax Disclosure [Abstract]
Federal statutory income tax rate	35.00%	35.00%	35.00%
State income taxes, net of the federal tax effect	5.70%	5.60%	5.20%
Meals and entertainment	0.30%	0.30%	0.40%
Disallowed officer's compensation	0.30%	0.30%	0.10%
Share-based compensation expense on incentive stock options and ESPP	0.00%	0.20%	(0.30%)
Tax-exempt interest income	(0.20%)	(0.30%)	(0.30%)
Low-income housing tax credit	(0.50%)	(0.50%)	(0.40%)
Effective Income Tax Rate Reconciliation, Change in Deferred Tax Assets Valuation Allowance, Percent	(0.40%)	(0.00%)	(0.00%)
Other, net	(0.30%)	0.40%	0.90%
Effective income tax rate	39.90%	41.00%	40.60%