Income Taxes Reconciliation between Federal Statutory Income Tax Rate and Effective Income Tax Rate (Detail)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Federal statutory income tax rate	35.00%	35.00%	35.00%
State income taxes, net of the federal tax effect	5.90%	5.70%	5.60%
Meals and entertainment	0.40%	0.30%	0.30%
Disallowed officer's compensation	0.10%	0.30%	0.30%
Share-based compensation expense on incentive stock options and ESPP	0.00%	0.00%	0.20%
Tax-exempt interest income	(0.20%)	(0.20%)	(0.30%)
Valuation allowance benefit	(0.30%)	(0.40%)	(0.00%)
Qualified affordable housing project tax credits	(0.50%)	(0.50%)	(0.50%)
Other, net	(0.90%)	(0.30%)	0.40%
Effective income tax rate	39.50%	39.90%	41.00%