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		6 Months Ended		12 Months Ended
	Jun. 30, 2016 USD ($) contracts	Jun. 30, 2015 USD ($) contracts	Jun. 30, 2016 USD ($) contracts	Jun. 30, 2015 USD ($) contracts	Jun. 30, 2016 USD ($) Loan	Jun. 30, 2015 USD ($) Loan
Financing Receivable, Modifications [Line Items]
TDRs, number	2	6	13	9	16	17
TDRs, Additions	$ 655	$ 1,317	$ 9,378	$ 1,611	$ 9,801	$ 6,093
Extension at Below Market Terms
Financing Receivable, Modifications [Line Items]
TDRs, number | contracts	2	6	12	9
TDRs, Additions	$ 655	$ 1,317	$ 9,218	$ 1,611
Reduction of Interest Rate
Financing Receivable, Modifications [Line Items]
TDRs, number | contracts	1	2	5	4
TDRs, Additions	$ 380	$ 372	$ 7,736	$ 452
Modification to Interest Only Payments
Financing Receivable, Modifications [Line Items]
TDRs, number | contracts	1	1	1	2
TDRs, Additions	$ 380	$ 169	$ 380	$ 219
Forgiveness of Debt
Financing Receivable, Modifications [Line Items]
TDRs, number | contracts	1	0	1	0
TDRs, Additions	$ 275	$ 0	$ 275	$ 0
Residential real estate and other
Financing Receivable, Modifications [Line Items]
TDRs, number	1	5	2	8	3	13
TDRs, Additions	$ 380	$ 1,148	$ 540	$ 1,442	$ 762	$ 3,058
Residential real estate and other | Extension at Below Market Terms
Financing Receivable, Modifications [Line Items]
TDRs, number | contracts	1	5	1	8
TDRs, Additions	$ 380	$ 1,148	$ 380	$ 1,442
Residential real estate and other | Reduction of Interest Rate
Financing Receivable, Modifications [Line Items]
TDRs, number | contracts	1	2	2	4
TDRs, Additions	$ 380	$ 372	$ 540	$ 452
Residential real estate and other | Modification to Interest Only Payments
Financing Receivable, Modifications [Line Items]
TDRs, number | contracts	1		1	1
TDRs, Additions	$ 380		$ 380	$ 50
Residential real estate and other | Forgiveness of Debt
Financing Receivable, Modifications [Line Items]
TDRs, number | contracts	0	0	0	0
TDRs, Additions	$ 0	$ 0	$ 0	$ 0
Commercial, industrial and other | Commercial
Financing Receivable, Modifications [Line Items]
TDRs, number	1	0	2	0	2	1
TDRs, Additions	$ 275	$ 0	$ 317	$ 0	$ 317	$ 1,461
Commercial, industrial and other | Commercial | Extension at Below Market Terms
Financing Receivable, Modifications [Line Items]
TDRs, number | contracts	1	0	2	0
TDRs, Additions	$ 275	$ 0	$ 317	$ 0
Commercial, industrial and other | Commercial | Reduction of Interest Rate
Financing Receivable, Modifications [Line Items]
TDRs, number | contracts	0	0	0	0
TDRs, Additions	$ 0	$ 0	$ 0	$ 0
Commercial, industrial and other | Commercial | Modification to Interest Only Payments
Financing Receivable, Modifications [Line Items]
TDRs, number | contracts	0	0	0	0
TDRs, Additions	$ 0	$ 0	$ 0	$ 0
Commercial, industrial and other | Commercial | Forgiveness of Debt
Financing Receivable, Modifications [Line Items]
TDRs, number | contracts	1	0	1	0
TDRs, Additions	$ 275	$ 0	$ 275	$ 0
Office | Commercial real estate
Financing Receivable, Modifications [Line Items]
TDRs, number	0	0	1	1	1	1
TDRs, Additions	$ 0	$ 0	$ 450	$ 169	$ 450	$ 720
Office | Commercial real estate | Extension at Below Market Terms
Financing Receivable, Modifications [Line Items]
TDRs, number | contracts	0	0	1	1
TDRs, Additions	$ 0	$ 0	$ 450	$ 169
Office | Commercial real estate | Reduction of Interest Rate
Financing Receivable, Modifications [Line Items]
TDRs, number | contracts	0	0	0	0
TDRs, Additions	$ 0	$ 0	$ 0	$ 0
Office | Commercial real estate | Modification to Interest Only Payments
Financing Receivable, Modifications [Line Items]
TDRs, number | contracts	0	0	0	1
TDRs, Additions	$ 0	$ 0	$ 0	$ 169
Office | Commercial real estate | Forgiveness of Debt
Financing Receivable, Modifications [Line Items]
TDRs, number | contracts	0	0	0	0
TDRs, Additions	$ 0	$ 0	$ 0	$ 0
Industrial | Commercial real estate
Financing Receivable, Modifications [Line Items]
TDRs, number	0	1	6	0	6	2
TDRs, Additions	$ 0	$ 169	$ 7,921	$ 0	$ 7,921	$ 854
Industrial | Commercial real estate | Extension at Below Market Terms
Financing Receivable, Modifications [Line Items]
TDRs, number | contracts	0	1	6	0
TDRs, Additions	$ 0	$ 169	$ 7,921	$ 0
Industrial | Commercial real estate | Reduction of Interest Rate
Financing Receivable, Modifications [Line Items]
TDRs, number | contracts	0	0	3	0
TDRs, Additions	$ 0	$ 0	$ 7,196	$ 0
Industrial | Commercial real estate | Modification to Interest Only Payments
Financing Receivable, Modifications [Line Items]
TDRs, number | contracts	0	1	0	0
TDRs, Additions	$ 0	$ 169	$ 0	$ 0
Industrial | Commercial real estate | Forgiveness of Debt
Financing Receivable, Modifications [Line Items]
TDRs, number | contracts	0	0	0	0
TDRs, Additions	$ 0	$ 0	$ 0	$ 0
Mixed use and other | Commercial real estate
Financing Receivable, Modifications [Line Items]
TDRs, number	0	0	2	0	4	0
TDRs, Additions	$ 0	$ 0	$ 150	$ 0	$ 351	$ 0
Mixed use and other | Commercial real estate | Extension at Below Market Terms
Financing Receivable, Modifications [Line Items]
TDRs, number | contracts	0	0	2	0
TDRs, Additions	$ 0	$ 0	$ 150	$ 0
Mixed use and other | Commercial real estate | Reduction of Interest Rate
Financing Receivable, Modifications [Line Items]
TDRs, number | contracts	0	0	0	0
TDRs, Additions	$ 0	$ 0	$ 0	$ 0
Mixed use and other | Commercial real estate | Modification to Interest Only Payments
Financing Receivable, Modifications [Line Items]
TDRs, number | contracts	0	0	0	0
TDRs, Additions	$ 0	$ 0	$ 0	$ 0
Mixed use and other | Commercial real estate | Forgiveness of Debt
Financing Receivable, Modifications [Line Items]
TDRs, number | contracts	0	0	0	0
TDRs, Additions	$ 0	$ 0	$ 0	$ 0