Allowance for Loan Losses, Allowance for Losses on Lending-Related Commitments and Impaired Loans (Summary of the Post-Modification Balance of TDRs) (Detail) $ in Thousands		3 Months Ended				12 Months Ended
		Mar. 31, 2016 USD ($) contracts		Mar. 31, 2015 USD ($) contracts		Mar. 31, 2016 USD ($) Loan	[3],[4]	Mar. 31, 2015 USD ($) Loan	[3],[4]
Financing Receivable, Modifications [Line Items]
TDRs, number		11	[1],[2]	3	[1],[2]	20		18
TDRs, Additions		$ 8,723	[1],[2]	$ 294	[1],[2]	$ 10,463		$ 7,017
Extension at Below Market Terms
Financing Receivable, Modifications [Line Items]
TDRs, number | contracts	[1]	10		3
TDRs, Additions	[1]	$ 8,563		$ 294
Reduction of Interest Rate
Financing Receivable, Modifications [Line Items]
TDRs, number | contracts	[1]	4		2
TDRs, Additions	[1]	$ 7,356		$ 80
Modification to Interest Only Payments
Financing Receivable, Modifications [Line Items]
TDRs, number | contracts	[1]	0		1
TDRs, Additions	[1]	$ 0		$ 50
Forgiveness of Debt
Financing Receivable, Modifications [Line Items]
TDRs, number | contracts	[1]	0		0
TDRs, Additions	[1]	$ 0		$ 0
Residential real estate and other
Financing Receivable, Modifications [Line Items]
TDRs, number		1	[1],[2]	3	[1],[2]	7		9
TDRs, Additions		$ 160	[1],[2]	$ 294	[1],[2]	$ 1,530		$ 2,131
Residential real estate and other | Extension at Below Market Terms
Financing Receivable, Modifications [Line Items]
TDRs, number | contracts	[1]	0		3
TDRs, Additions	[1]	$ 0		$ 294
Residential real estate and other | Reduction of Interest Rate
Financing Receivable, Modifications [Line Items]
TDRs, number | contracts	[1]	1		2
TDRs, Additions	[1]	$ 160		$ 80
Residential real estate and other | Modification to Interest Only Payments
Financing Receivable, Modifications [Line Items]
TDRs, number | contracts	[1]	0		1
TDRs, Additions	[1]	$ 0		$ 50
Residential real estate and other | Forgiveness of Debt
Financing Receivable, Modifications [Line Items]
TDRs, number | contracts	[1]	0		0
TDRs, Additions	[1]	$ 0		$ 0
Commercial, industrial and other | Commercial
Financing Receivable, Modifications [Line Items]
TDRs, number		1	[1],[2]	0	[1],[2]	1		1
TDRs, Additions		$ 42	[1],[2]	$ 0	[1],[2]	$ 42		$ 1,461
Commercial, industrial and other | Commercial | Extension at Below Market Terms
Financing Receivable, Modifications [Line Items]
TDRs, number | contracts	[1]	1		0
TDRs, Additions	[1]	$ 42		$ 0
Commercial, industrial and other | Commercial | Reduction of Interest Rate
Financing Receivable, Modifications [Line Items]
TDRs, number | contracts	[1]	0		0
TDRs, Additions	[1]	$ 0		$ 0
Commercial, industrial and other | Commercial | Modification to Interest Only Payments
Financing Receivable, Modifications [Line Items]
TDRs, number | contracts	[1]	0		0
TDRs, Additions	[1]	$ 0		$ 0
Commercial, industrial and other | Commercial | Forgiveness of Debt
Financing Receivable, Modifications [Line Items]
TDRs, number | contracts	[1]	0		0
TDRs, Additions	[1]	$ 0		$ 0
Office | Commercial real estate
Financing Receivable, Modifications [Line Items]
TDRs, number		1	[1],[2]	0	[1],[2]	1		2
TDRs, Additions		$ 450	[1],[2]	$ 0	[1],[2]	$ 450		$ 1,510
Office | Commercial real estate | Extension at Below Market Terms
Financing Receivable, Modifications [Line Items]
TDRs, number | contracts	[1]	1		0
TDRs, Additions	[1]	$ 450		$ 0
Office | Commercial real estate | Reduction of Interest Rate
Financing Receivable, Modifications [Line Items]
TDRs, number | contracts	[1]	0		0
TDRs, Additions	[1]	$ 0		$ 0
Office | Commercial real estate | Modification to Interest Only Payments
Financing Receivable, Modifications [Line Items]
TDRs, number | contracts	[1]	0		0
TDRs, Additions	[1]	$ 0		$ 0
Office | Commercial real estate | Forgiveness of Debt
Financing Receivable, Modifications [Line Items]
TDRs, number | contracts	[1]	0		0
TDRs, Additions	[1]	$ 0		$ 0
Industrial | Commercial real estate
Financing Receivable, Modifications [Line Items]
TDRs, number		6	[1],[2]	0	[1],[2]	7		1
TDRs, Additions		$ 7,921	[1],[2]	$ 0	[1],[2]	$ 8,090		$ 685
Industrial | Commercial real estate | Extension at Below Market Terms
Financing Receivable, Modifications [Line Items]
TDRs, number | contracts	[1]	6		0
TDRs, Additions	[1]	$ 7,921		$ 0
Industrial | Commercial real estate | Reduction of Interest Rate
Financing Receivable, Modifications [Line Items]
TDRs, number | contracts	[1]	3		0
TDRs, Additions	[1]	$ 7,196		$ 0
Industrial | Commercial real estate | Modification to Interest Only Payments
Financing Receivable, Modifications [Line Items]
TDRs, number | contracts	[1]	0		0
TDRs, Additions	[1]	$ 0		$ 0
Industrial | Commercial real estate | Forgiveness of Debt
Financing Receivable, Modifications [Line Items]
TDRs, number | contracts	[1]	0		0
TDRs, Additions	[1]	$ 0		$ 0
Mixed use and other | Commercial real estate
Financing Receivable, Modifications [Line Items]
TDRs, number		2	[1],[2]	0	[1],[2]	4		4
TDRs, Additions		$ 150	[1],[2]	$ 0	[1],[2]	$ 351		$ 1,049
Mixed use and other | Commercial real estate | Extension at Below Market Terms
Financing Receivable, Modifications [Line Items]
TDRs, number | contracts	[1]	2		0
TDRs, Additions	[1]	$ 150		$ 0
Mixed use and other | Commercial real estate | Reduction of Interest Rate
Financing Receivable, Modifications [Line Items]
TDRs, number | contracts	[1]	0		0
TDRs, Additions	[1]	$ 0		$ 0
Mixed use and other | Commercial real estate | Modification to Interest Only Payments
Financing Receivable, Modifications [Line Items]
TDRs, number | contracts	[1]	0		0
TDRs, Additions	[1]	$ 0		$ 0
Mixed use and other | Commercial real estate | Forgiveness of Debt
Financing Receivable, Modifications [Line Items]
TDRs, number | contracts	[1]	0		0
TDRs, Additions	[1]	$ 0		$ 0

[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.