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, 2016	Dec. 31, 2015	Dec. 31, 2014
Schedule of Equity Method Investments [Line Items]
Affordable housing tax credits and other tax benefits	$ 5,013	$ 4,709	$ 5,296
Other tax credit investment credits and tax benefits	33,294	23,877	14,357
Total reduction in income tax expense	38,307	28,586	19,653
Amortization Recorded in Non-Interest Expenses
Schedule of Equity Method Investments [Line Items]
Affordable housing tax credit investment losses	2,077	2,594	3,184
Affordable housing tax credit investment impairment losses	450	1,321	3,211
Other tax credit investment losses	790	1,079	2,359
Other tax credit investment impairment losses	31,427	22,318	15,442
Total amortization of tax credit investments recorded in non-interest expense	$ 34,744	$ 27,312	$ 24,196