Tax Credit Investments Tax Credit Investments - Affordable Housing Tax Credit Investments and Other Tax Credit Investments (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Schedule of Equity Method Investments [Line Items]
Affordable housing tax credits and other tax benefits	$ 1,065	$ 1,731
Other tax credit investment credits and tax benefits	3,268	3,618
Total reduction in income tax expense	4,333	5,349
Non-Interest Expenses [Member]
Schedule of Equity Method Investments [Line Items]
Affordable housing tax credit investment losses	584	677
Affordable housing tax credit investment impairment losses	140	488
Other tax credit investment losses	74	297
Other tax credit investment impairment losses	6,466	3,034
Total amortization of tax credit investments recorded in non-interest expense	$ 7,264	$ 4,496