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	Jun. 30, 2016	Dec. 31, 2015	Jun. 30, 2015
Financing Receivable, Impaired [Line Items]
Impaired loans with an allowance for loan loss required	$ 42,968	$ 49,961	$ 50,748
Impaired loans with no allowance for loan loss required	53,008	51,294	52,609
Total impaired loans	95,976	101,255	103,357
Allowance for loan losses related to impaired loans	6,611	6,380	10,075
Financing Receivable
Financing Receivable, Impaired [Line Items]
Allowance for loan losses related to impaired loans	3,200
TDRs	$ 49,635	$ 51,853	$ 62,776