Loans, Leases and Allowance for Credit Losses - Average Investment in Impaired Loans by Loan Class (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Financing Receivable, Impaired [Line Items]
Total average investment in impaired loans by loan class	$ 169,758	$ 182,670	$ 214,499
Residential real estate [Member]
Financing Receivable, Impaired [Line Items]
Total average investment in impaired loans by loan class	25,223	33,339	35,639
Consumer [Member]
Financing Receivable, Impaired [Line Items]
Total average investment in impaired loans by loan class	508	604	1,104
Commercial real estate [Member] | Owner occupied [Member]
Financing Receivable, Impaired [Line Items]
Total average investment in impaired loans by loan class	37,048	49,452	57,147
Commercial real estate [Member] | Non-owner occupied [Member]
Financing Receivable, Impaired [Line Items]
Total average investment in impaired loans by loan class	68,821	56,110	57,284
Commercial real estate [Member] | Multi-family [Member]
Financing Receivable, Impaired [Line Items]
Total average investment in impaired loans by loan class	0	89	872
Commercial and industrial [Member] | Commercial [Member]
Financing Receivable, Impaired [Line Items]
Total average investment in impaired loans by loan class	16,168	15,023	24,094
Commercial and industrial [Member] | Leases [Member]
Financing Receivable, Impaired [Line Items]
Total average investment in impaired loans by loan class	410	727	874
Construction and land development [Member] | Construction [Member]
Financing Receivable, Impaired [Line Items]
Total average investment in impaired loans by loan class	0	0	986
Construction and land development [Member] | Land [Member]
Financing Receivable, Impaired [Line Items]
Total average investment in impaired loans by loan class	$ 21,580	$ 27,326	$ 36,499