Income Taxes (Detail) - Components of Effective Tax Rate - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Tax Disclosure [Abstract]
Statutory federal income tax rate (amount)	$ 41,934	$ 35,167	$ 44,807
Statutory federal income tax rate (percent of pretax income)	35.00%	35.00%	35.00%
Tax-exempt income, net of interest expense disallowance (amount)	$ (6,752)	$ (7,520)	$ (7,877)
Tax-exempt income, net of interest expense disallowance (percent of pretax income)	(5.60%)	(7.50%)	(6.20%)
State income tax, net of federal income tax effect (amount)	$ 4,665	$ 4,503	$ 8,142
State income tax, net of federal income tax effect (percent of pretax income)	3.90%	4.50%	6.40%
Other (amount)	$ (2,100)	$ (980)	$ 3,643
Net (percent of pretax income)	(1.80%)	(1.00%)	2.90%
Total income tax expense	$ 37,747	$ 31,170	$ 48,715
Effective tax rate	31.50%	31.00%	38.10%