Loans, Leases and Allowance for Credit Losses - Average Investment in Impaired Loans by Loan Class (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Financing Receivable, Impaired [Line Items]
Total average investment in impaired loans by loan class	$ 122,545	$ 162,109
Residential real estate [Member]
Financing Receivable, Impaired [Line Items]
Total average investment in impaired loans by loan class	15,764	18,911
Consumer [Member]
Financing Receivable, Impaired [Line Items]
Total average investment in impaired loans by loan class	329	353
Troubled Debt Restructured Loans [Member]
Financing Receivable, Impaired [Line Items]
Total average investment in impaired loans by loan class	78,000	126,100
Commercial real estate [Member] | Owner occupied [Member]
Financing Receivable, Impaired [Line Items]
Total average investment in impaired loans by loan class	21,737	42,927
Commercial real estate [Member] | Non-owner occupied [Member]
Financing Receivable, Impaired [Line Items]
Total average investment in impaired loans by loan class	33,033	65,080
Commercial real estate [Member] | Multi-family [Member]
Financing Receivable, Impaired [Line Items]
Total average investment in impaired loans by loan class	0	0
Commercial and industrial [Member] | Commercial [Member]
Financing Receivable, Impaired [Line Items]
Total average investment in impaired loans by loan class	31,733	13,269
Commercial and industrial [Member] | Leases [Member]
Financing Receivable, Impaired [Line Items]
Total average investment in impaired loans by loan class	2,049	357
Construction and land development [Member] | Construction [Member]
Financing Receivable, Impaired [Line Items]
Total average investment in impaired loans by loan class	0	0
Construction and land development [Member] | Land [Member]
Financing Receivable, Impaired [Line Items]
Total average investment in impaired loans by loan class	$ 17,900	$ 21,212