Allowance for Loan Losses, Allowance for Losses on Lending-Related Commitments and Impaired Loans (Summary of TDRs Subsequent Default Under the Restructured Terms) (Detail) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2016 USD ($) contracts Loan	Sep. 30, 2015 USD ($) contracts Loan	Sep. 30, 2016 USD ($) contracts Loan	Sep. 30, 2015 USD ($) contracts Loan	Sep. 30, 2016 USD ($) Loan	Sep. 30, 2015 USD ($) Loan
Troubled Debt Restructuring, Debtor, Subsequent Periods [Line Items]
Total, Count	2	1	15	10	17	15
Total, Balance	$ 71	$ 222	$ 9,449	$ 1,833	$ 9,650	$ 5,648
Subsequent Default, Count | Loan	5	3	7	4
Subsequent Default, Balance	$ 1,191	$ 816	$ 1,392	$ 1,030
Commercial | Commercial, industrial and other
Troubled Debt Restructuring, Debtor, Subsequent Periods [Line Items]
Total, Count	1	0	3	0	3	1
Total, Balance	$ 28	$ 0	$ 345	$ 0	$ 345	$ 1,461
Subsequent Default, Count | Loan	0	0	0	0
Subsequent Default, Balance	$ 0	$ 0	$ 0	$ 0
Commercial real estate | Office
Troubled Debt Restructuring, Debtor, Subsequent Periods [Line Items]
Total, Count	0	0	1		1	1
Total, Balance	$ 0	$ 0	$ 450		$ 450	$ 720
Subsequent Default, Count | Loan	1	0	1	0
Subsequent Default, Balance	$ 450	$ 0	$ 450	$ 0
Commercial real estate | Industrial
Troubled Debt Restructuring, Debtor, Subsequent Periods [Line Items]
Total, Count	0	0	6	1	6	2
Total, Balance	$ 0	$ 0	$ 7,921	$ 169	$ 7,921	$ 854
Subsequent Default, Count | Loan	3	1	3	1
Subsequent Default, Balance	$ 725	$ 685	$ 725	$ 685
Commercial real estate | Mixed use and other
Troubled Debt Restructuring, Debtor, Subsequent Periods [Line Items]
Total, Count	0	0	2	0	4	0
Total, Balance	$ 0	$ 0	$ 150	$ 0	$ 351	$ 0
Subsequent Default, Count | Loan	1	0	3	0
Subsequent Default, Balance	$ 16	$ 0	$ 217	$ 0
Residential real estate and other
Troubled Debt Restructuring, Debtor, Subsequent Periods [Line Items]
Total, Count	1	1	3	9	3	11
Total, Balance	$ 43	$ 222	$ 583	$ 1,664	$ 583	$ 2,613
Subsequent Default, Count | Loan	0	2	0	3
Subsequent Default, Balance	$ 0	$ 131	$ 0	$ 345