Loans and Leases - Reserve for Commercial TDRs Included in Allowance for Credit Losses (Detail) - USD ($) $ in Thousands	Sep. 30, 2016	Jun. 30, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Dec. 31, 2014
Financing Receivable, Modifications [Line Items]
Reserves in allowance for loan losses, TDRs	$ 156,894	$ 154,369	$ 142,012	$ 136,183	$ 131,141	$ 125,926
Total Commercial Loans and Leases [Member]
Financing Receivable, Modifications [Line Items]
Reserves in allowance for loan losses, TDRs	99,282	$ 98,950	85,305	$ 79,501	$ 74,400	$ 72,631
Specific Reserves [Member] | Total Commercial Loans and Leases [Member]
Financing Receivable, Modifications [Line Items]
Reserves in allowance for loan losses, TDRs	608		300
Pooled Reserves for Individual Loans [Member] | Total Commercial Loans and Leases [Member]
Financing Receivable, Modifications [Line Items]
Reserves in allowance for loan losses, TDRs	$ 302		$ 929