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, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Schedule of Equity Method Investments [Line Items]
Affordable housing tax credits and other tax benefits	$ 1,660	$ 2,164	$ 4,774	$ 6,148
Other tax credit investment credits and tax benefits	7,510	3,269	16,031	9,953
Total reduction in income tax expense	9,170	5,433	20,805	16,101
Non-Interest Expenses [Member]
Schedule of Equity Method Investments [Line Items]
Affordable housing tax credit investment losses	543	1,073	1,516	2,291
Affordable housing tax credit investment impairment losses	451	375	979	2,889
Other tax credit investment losses	144	747	934	1,829
Other tax credit investment impairment losses	4,086	2,435	10,802	7,139
Total amortization of tax credit investments recorded in non-interest expense	$ 5,224	$ 4,630	$ 14,231	$ 14,148