Tax Credit Investments Tax Credit Investments - Affordable Housing Tax Credit Investments and Other Tax Credit Investments (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Schedule of Equity Method Investments [Line Items]
Affordable housing tax credits and other tax benefits	$ 1,383	$ 2,591	$ 3,114	$ 3,984
Other tax credit investment credits and tax benefits	4,903	3,496	8,521	6,684
Total reduction in income tax expense	6,286	6,087	11,635	10,668
Non-Interest Expenses [Member]
Schedule of Equity Method Investments [Line Items]
Affordable housing tax credit investment losses	296	778	973	1,218
Affordable housing tax credit investment impairment losses	40	2,514	528	2,514
Other tax credit investment losses	493	684	790	1,082
Other tax credit investment impairment losses	3,682	1,826	6,716	4,704
Total amortization of tax credit investments recorded in non-interest expense	$ 4,511	$ 5,802	$ 9,007	$ 9,518