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) (USD $) In Thousands, unless otherwise specified	3 Months Ended				12 Months Ended
	Mar. 31, 2015 contracts		Mar. 31, 2014 contracts		Mar. 31, 2015 contracts		Mar. 31, 2014 contracts
Troubled Debt Restructuring, Debtor, Subsequent Periods [Line Items]
Total, Count	3	[1],[2]	6	[1],[2]	18	[1],[3]	27	[1],[3]
Total, Balance	$ 294	[1],[2]	$ 5,245	[1],[2]	$ 7,017	[1],[3]	$ 25,648	[1],[3]
Subsequent Default, Count	7	[1],[4]	8	[1],[4]
Subsequent Default, Balance	2,048	[1],[4]	9,984	[1],[4]
Commercial | Commercial and industrial
Troubled Debt Restructuring, Debtor, Subsequent Periods [Line Items]
Total, Count	0	[1],[2]	1	[1],[2]	1	[1],[3]	1	[1],[3]
Total, Balance	0	[1],[2]	88	[1],[2]	1,461	[1],[3]	88	[1],[3]
Subsequent Default, Count	0	[1],[4]	0	[1],[4]
Subsequent Default, Balance	0	[1],[4]	0	[1],[4]
Commercial real-estate | Commercial construction
Troubled Debt Restructuring, Debtor, Subsequent Periods [Line Items]
Total, Count					0	[1],[3]	3	[1],[3]
Total, Balance					0	[1],[3]	6,120	[1],[3]
Subsequent Default, Count	0	[1],[4]	3	[1],[4]
Subsequent Default, Balance	0	[1],[4]	6,120	[1],[4]
Commercial real-estate | Land
Troubled Debt Restructuring, Debtor, Subsequent Periods [Line Items]
Total, Count					0	[1],[3]	1	[1],[3]
Total, Balance					0	[1],[3]	2,352	[1],[3]
Subsequent Default, Count	0	[1],[4]	0	[1],[4]
Subsequent Default, Balance	0	[1],[4]	0	[1],[4]
Commercial real-estate | Office
Troubled Debt Restructuring, Debtor, Subsequent Periods [Line Items]
Total, Count					2	[1],[3]	4	[1],[3]
Total, Balance					1,510	[1],[3]	4,021	[1],[3]
Subsequent Default, Count	1	[1],[4]	3	[1],[4]
Subsequent Default, Balance	790	[1],[4]	3,465	[1],[4]
Commercial real-estate | Industrial
Troubled Debt Restructuring, Debtor, Subsequent Periods [Line Items]
Total, Count	0	[1],[2]	1	[1],[2]	1	[1],[3]	2	[1],[3]
Total, Balance	0	[1],[2]	1,078	[1],[2]	685	[1],[3]	2,027	[1],[3]
Subsequent Default, Count	0	[1],[4]	0	[1],[4]
Subsequent Default, Balance	0	[1],[4]	0	[1],[4]
Commercial real-estate | Retail
Troubled Debt Restructuring, Debtor, Subsequent Periods [Line Items]
Total, Count	0	[1],[2]	1	[1],[2]	0	[1],[3]	1	[1],[3]
Total, Balance	0	[1],[2]	202	[1],[2]	0	[1],[3]	202	[1],[3]
Subsequent Default, Count	0	[1],[4]	0	[1],[4]
Subsequent Default, Balance	0	[1],[4]	0	[1],[4]
Commercial real-estate | Multi-family
Troubled Debt Restructuring, Debtor, Subsequent Periods [Line Items]
Total, Count					1	[1],[3]	0	[1],[3]
Total, Balance					181	[1],[3]	0	[1],[3]
Subsequent Default, Count	1	[1],[4]	0	[1],[4]
Subsequent Default, Balance	181	[1],[4]	0	[1],[4]
Commercial real-estate | Mixed use and other
Troubled Debt Restructuring, Debtor, Subsequent Periods [Line Items]
Total, Count	0	[1],[2]	3	[1],[2]	4	[1],[3]	9	[1],[3]
Total, Balance	0	[1],[2]	3,877	[1],[2]	1,049	[1],[3]	8,919	[1],[3]
Subsequent Default, Count	3	[1],[4]	2	[1],[4]
Subsequent Default, Balance	816	[1],[4]	399	[1],[4]
Residential real estate and other
Troubled Debt Restructuring, Debtor, Subsequent Periods [Line Items]
Total, Count	3	[1],[2]	0	[1],[2]	9	[1],[3]	6	[1],[3]
Total, Balance	294	[1],[2]	0	[1],[2]	2,131	[1],[3]	1,919	[1],[3]
Subsequent Default, Count	2	[1],[4]	0	[1],[4]
Subsequent Default, Balance	$ 261	[1],[4]	$ 0	[1],[4]

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

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