Allowance for Loan Losses, Allowance for Losses on Lending-Related Commitments and Impaired Loans 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				6 Months Ended				12 Months Ended
		Jun. 30, 2015 USD ($) contracts		Jun. 30, 2014 USD ($) contracts		Jun. 30, 2015 USD ($) contracts		Jun. 30, 2014 USD ($) contracts		Jun. 30, 2015 USD ($) contracts		Jun. 30, 2014 USD ($) contracts
Troubled Debt Restructuring, Debtor, Subsequent Periods [Line Items]
Total, Count | contracts		6	[1],[2]	7	[1],[2]	9	[1],[2]	13	[1],[2]	17	[3],[4]	22	[3],[4]
Total, Balance		$ 1,317	[1],[2]	$ 2,240	[1],[2]	$ 1,611	[1],[2]	$ 7,485	[1],[2]	$ 6,093	[3],[4]	$ 13,420	[3],[4]
Subsequent Default, Count | contracts	[3],[5]	4		6		4		6
Subsequent Default, Balance	[3],[5]	$ 833		$ 4,176		$ 833		$ 4,176
Commercial | Commercial and industrial
Troubled Debt Restructuring, Debtor, Subsequent Periods [Line Items]
Total, Count | contracts		0	[1],[2]	0	[1],[2]	0	[1],[2]	1	[1],[2]	1	[3],[4]	1	[3],[4]
Total, Balance		$ 0	[1],[2]	$ 0	[1],[2]	$ 0	[1],[2]	$ 88	[1],[2]	$ 1,461	[3],[4]	$ 88	[3],[4]
Subsequent Default, Count | contracts	[3],[5]	0		0		0		0
Subsequent Default, Balance	[3],[5]	$ 0		$ 0		$ 0		$ 0
Commercial real estate | Land
Troubled Debt Restructuring, Debtor, Subsequent Periods [Line Items]
Total, Count | contracts	[3],[4]									0		1
Total, Balance	[3],[4]									$ 0		$ 2,352
Subsequent Default, Count | contracts	[3],[5]	0		1		0		1
Subsequent Default, Balance	[3],[5]	$ 0		$ 2,352		$ 0		$ 2,352
Commercial real estate | Office
Troubled Debt Restructuring, Debtor, Subsequent Periods [Line Items]
Total, Count | contracts		0	[1],[2]	1	[1],[2]	0	[1],[2]	1	[1],[2]	1	[3],[4]	2	[3],[4]
Total, Balance		$ 0	[1],[2]	$ 790	[1],[2]	$ 0	[1],[2]	$ 790	[1],[2]	$ 720	[3],[4]	$ 1,345	[3],[4]
Subsequent Default, Count | contracts	[3],[5]	0		0		0		0
Subsequent Default, Balance	[3],[5]	$ 0		$ 0		$ 0		$ 0
Commercial real estate | Industrial
Troubled Debt Restructuring, Debtor, Subsequent Periods [Line Items]
Total, Count | contracts		1	[1],[2]	0	[1],[2]	1	[1],[2]	1	[1],[2]	2	[3],[4]	1	[3],[4]
Total, Balance		$ 169	[1],[2]	$ 0	[1],[2]	$ 169	[1],[2]	$ 1,078	[1],[2]	$ 854	[3],[4]	$ 1,078	[3],[4]
Subsequent Default, Count | contracts	[3],[5]	0		1		0		1
Subsequent Default, Balance	[3],[5]	$ 0		$ 1,078		$ 0		$ 1,078
Commercial real estate | Retail
Troubled Debt Restructuring, Debtor, Subsequent Periods [Line Items]
Total, Count | contracts		0	[1],[2]	0	[1],[2]	0	[1],[2]	1	[1],[2]	0	[3],[4]	1	[3],[4]
Total, Balance		$ 0	[1],[2]	$ 0	[1],[2]	$ 0	[1],[2]	$ 202	[1],[2]	$ 0	[3],[4]	$ 202	[3],[4]
Subsequent Default, Count | contracts	[3],[5]	0		0		0		0
Subsequent Default, Balance	[3],[5]	$ 0		$ 0		$ 0		$ 0
Commercial real estate | Multi-family
Troubled Debt Restructuring, Debtor, Subsequent Periods [Line Items]
Total, Count | contracts		0	[1],[2]	1	[1],[2]	0	[1],[2]	1	[1],[2]	0	[3],[4]	1	[3],[4]
Total, Balance		$ 0	[1],[2]	$ 181	[1],[2]	$ 0	[1],[2]	$ 181	[1],[2]	$ 0	[3],[4]	$ 181	[3],[4]
Subsequent Default, Count | contracts	[3],[5]	0		0		0		0
Subsequent Default, Balance	[3],[5]	$ 0		$ 0		$ 0		$ 0
Commercial real estate | Mixed use and other
Troubled Debt Restructuring, Debtor, Subsequent Periods [Line Items]
Total, Count | contracts		0	[1],[2]	4	[1],[2]	0	[1],[2]	7	[1],[2]	0	[3],[4]	11	[3],[4]
Total, Balance		$ 0	[1],[2]	$ 1,049	[1],[2]	$ 0	[1],[2]	$ 4,926	[1],[2]	$ 0	[3],[4]	$ 6,436	[3],[4]
Subsequent Default, Count | contracts	[3],[5]	0		3		0		3
Subsequent Default, Balance	[3],[5]	$ 0		$ 577		$ 0		$ 577
Residential real estate and other
Troubled Debt Restructuring, Debtor, Subsequent Periods [Line Items]
Total, Count | contracts		5	[1],[2]	1	[1],[2]	8	[1],[2]	1	[1],[2]	13	[3],[4]	4	[3],[4]
Total, Balance		$ 1,148	[1],[2]	$ 220	[1],[2]	$ 1,442	[1],[2]	$ 220	[1],[2]	$ 3,058	[3],[4]	$ 1,738	[3],[4]
Subsequent Default, Count | contracts	[3],[5]	4		1		4		1
Subsequent Default, Balance	[3],[5]	$ 833		$ 169		$ 833		$ 169

[1] Balances represent the recorded investment in the loan at the time of the restructuring.

[2] TDRs may have more than one modification representing a concession. As such, TDRs during the period may be represented in more than one of the categories noted above.

[3] Balances represent the recorded investment in the loan at the time of the restructuring.

[4] Total TDRs represent all loans restructured in TDRs during the previous twelve months from the date indicated.

[5] TDRs considered to be in payment default are over 30 days past-due subsequent to the restructuring.