Tax Credit Investments Tax Credit Investments - Affordable Housing Tax Credit Investments and Other Tax Credit Investments (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Schedule of Equity Method Investments [Line Items]
Affordable housing tax credits and other tax benefits	$ 1,065	$ 1,660	$ 3,195	$ 4,774
Other tax credit investment credits and tax benefits	6,118	7,510	12,654	16,031
Total reduction in income tax expense	7,183	9,170	15,849	20,805
Non-Interest Expenses
Schedule of Equity Method Investments [Line Items]
Affordable housing tax credit investment losses	33	543	1,392	1,516
Affordable housing tax credit investment impairment losses	128	451	328	979
Other tax credit investment losses	107	144	775	934
Other tax credit investment impairment losses	6,182	4,086	18,865	10,802
Total amortization of tax credit investments recorded in non-interest expense	$ 6,450	$ 5,224	$ 21,360	$ 14,231