Allowance for Loan Losses, Allowance for Losses on Lending-Related Commitments and Impaired Loans (Summary of Impaired Loans, Including Restructured Loans) (Detail) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015	Sep. 30, 2015
Financing Receivable, Impaired [Line Items]
Impaired loans with an allowance for loan loss required	$ 39,022	$ 49,961	$ 51,113
Impaired loans with no allowance for loan loss required	51,518	51,294	61,914
Total impaired loans	90,540	101,255	113,027
Allowance for loan losses related to impaired loans	6,836	6,380	8,483
Financing Receivable
Financing Receivable, Impaired [Line Items]
Allowance for loan losses related to impaired loans	2,800
TDRs	$ 44,276	$ 51,853	$ 59,320