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		Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2015
Financing Receivable, Impaired [Line Items]
Impaired loans with an allowance for loan loss required	[1]	$ 50,710	$ 49,961	$ 48,610
Impaired loans with no allowance for loan loss required		45,400	51,294	63,794
Total impaired loans	[2]	96,110	101,255	112,404
Allowance for loan losses related to impaired loans		7,775	6,380	6,199
Financing Receivable
Financing Receivable, Impaired [Line Items]
Allowance for loan losses related to impaired loans		3,100
TDRs		$ 52,555	$ 51,853	$ 67,218

[1] These impaired loans require an allowance for loan losses because the estimated fair value of the loans or related collateral is less than the recorded investment in the loans.

[2] Impaired loans are considered by the Company to be non-accrual loans, TDRs or loans with principal and/or interest at risk, even if the loan is current with all payments of principal and interest.