Tax Credit Investments Tax Credit Investments - Affordable Housing Tax Credit Investments and Other Tax Credit Investments (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Schedule of Equity Method Investments [Line Items]
Affordable housing tax credits and other tax benefits	$ 4,709	$ 5,296	$ 4,722
Other tax credit investment credits and tax benefits	23,877	14,357	12,285
Total reduction in income tax expense	28,586	19,653	17,007
Amortization Recorded in Non-Interest Expenses [Member]
Schedule of Equity Method Investments [Line Items]
Affordable housing tax credit investment losses	2,594	3,184	1,755
Affordable housing tax credit investment impairment losses	1,321	3,211	913
Other tax credit investment losses	1,079	2,359	1,630
Other tax credit investment impairment losses	22,318	15,442	10,054
Total amortization of tax credit investments recorded in non-interest expense	$ 27,312	$ 24,196	$ 14,352