Loans, Leases and Allowance for Credit Losses - Average Investment in Impaired Loans by Loan Class (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Financing Receivable, Impaired [Line Items]
Total average investment in impaired loans by loan class	$ 150,151	$ 169,758	$ 182,670
Residential real estate [Member]
Financing Receivable, Impaired [Line Items]
Total average investment in impaired loans by loan class	18,453	25,223	33,339
Consumer [Member]
Financing Receivable, Impaired [Line Items]
Total average investment in impaired loans by loan class	383	508	604
Troubled Debt Restructured Loans [Member]
Financing Receivable, Impaired [Line Items]
Total average investment in impaired loans by loan class	113,900	126,600	141,800
Commercial real estate [Member] | Owner occupied [Member]
Financing Receivable, Impaired [Line Items]
Total average investment in impaired loans by loan class	34,912	37,048	49,452
Commercial real estate [Member] | Non-owner occupied [Member]
Financing Receivable, Impaired [Line Items]
Total average investment in impaired loans by loan class	56,360	68,821	56,110
Commercial real estate [Member] | Multi-family [Member]
Financing Receivable, Impaired [Line Items]
Total average investment in impaired loans by loan class	0	0	89
Commercial and industrial [Member] | Commercial [Member]
Financing Receivable, Impaired [Line Items]
Total average investment in impaired loans by loan class	17,534	16,168	15,023
Commercial and industrial [Member] | Leases [Member]
Financing Receivable, Impaired [Line Items]
Total average investment in impaired loans by loan class	2,948	410	727
Construction and land development [Member] | Construction [Member]
Financing Receivable, Impaired [Line Items]
Total average investment in impaired loans by loan class	0	0	0
Construction and land development [Member] | Land [Member]
Financing Receivable, Impaired [Line Items]
Total average investment in impaired loans by loan class	$ 19,561	$ 21,580	$ 27,326