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, 2019 USD ($) contracts	Jun. 30, 2018 USD ($) contracts	Jun. 30, 2019 USD ($) contracts	Jun. 30, 2018 USD ($) contracts	Jun. 30, 2019 USD ($) Loan	Jun. 30, 2018 USD ($) Loan
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs, number	30	12	60	19	112	32
TDRs, Additions	$ 9,489	$ 19,605	$ 33,207	$ 20,595	$ 41,854	$ 41,197
Extension at Below Market Terms
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs, number | contracts	30	9	52	16
TDRs, Additions	$ 9,489	$ 1,733	$ 14,483	$ 2,723
Reduction of Interest Rate
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs, number | contracts	10	4	16	6
TDRs, Additions	$ 2,492	$ 770	$ 4,039	$ 881
Modification to Interest Only Payments
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs, number | contracts	2	3	10	3
TDRs, Additions	$ 1,494	$ 17,872	$ 20,218	$ 17,872
Forgiveness of Debt
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs, number | contracts	0	0	0	0
TDRs, Additions	$ 0	$ 0	$ 0	$ 0
Residential real estate and other
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs, number	22	6	42	11	90	17
TDRs, Additions	$ 5,761	$ 1,332	$ 10,247	$ 2,167	$ 17,842	$ 2,833
Residential real estate and other | Extension at Below Market Terms
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs, number | contracts	22	6	42	11
TDRs, Additions	$ 5,761	$ 1,332	$ 10,247	$ 2,167
Residential real estate and other | Reduction of Interest Rate
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs, number | contracts	9	3	15	5
TDRs, Additions	$ 1,942	$ 685	$ 3,489	$ 796
Residential real estate and other | Modification to Interest Only Payments
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs, number | contracts	0	0	0	0
TDRs, Additions	$ 0	$ 0	$ 0	$ 0
Residential real estate and other | Forgiveness of Debt
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs, number | contracts	0	0	0	0
TDRs, Additions	$ 0	$ 0	$ 0	$ 0
Commercial, industrial and other | Commercial
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs, number	5	2	13	3	14	7
TDRs, Additions	$ 2,455	$ 12,827	$ 21,309	$ 12,923	$ 21,826	$ 16,603
Commercial, industrial and other | Commercial | Extension at Below Market Terms
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs, number | contracts	5	1	6	2
TDRs, Additions	$ 2,455	$ 77	$ 2,887	$ 173
Commercial, industrial and other | Commercial | Reduction of Interest Rate
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs, number | contracts	1	0	1	0
TDRs, Additions	$ 550	$ 0	$ 550	$ 0
Commercial, industrial and other | Commercial | Modification to Interest Only Payments
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs, number | contracts	2	1	9	1
TDRs, Additions	$ 1,494	$ 12,750	$ 19,916	$ 12,750
Commercial, industrial and other | Commercial | Forgiveness of Debt
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs, number | contracts	0	0	0	0
TDRs, Additions	$ 0	$ 0	$ 0	$ 0
Franchise | Commercial
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs, number				2	1	5
TDRs, Additions				$ 5,122	$ 35	$ 21,378
Franchise | Commercial | Extension at Below Market Terms
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs, number | contracts				0
TDRs, Additions				$ 0
Franchise | Commercial | Reduction of Interest Rate
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs, number | contracts				0
TDRs, Additions				$ 0
Franchise | Commercial | Modification to Interest Only Payments
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs, number | contracts				2
TDRs, Additions				$ 5,122
Franchise | Commercial | Forgiveness of Debt
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs, number | contracts				0
TDRs, Additions				$ 0
Asset-based lending | Commercial
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs, number		2	1		2
TDRs, Additions		$ 5,122	$ 76		$ 206
Asset-based lending | Commercial | Extension at Below Market Terms
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs, number | contracts		0	1
TDRs, Additions		$ 0	$ 76
Asset-based lending | Commercial | Reduction of Interest Rate
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs, number | contracts		0	0
TDRs, Additions		$ 0	$ 0
Asset-based lending | Commercial | Modification to Interest Only Payments
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs, number | contracts		2	0
TDRs, Additions		$ 5,122	$ 0
Asset-based lending | Commercial | Forgiveness of Debt
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs, number | contracts		0	0
TDRs, Additions		$ 0	$ 0
Leases | Commercial
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs, number		1		1		1
TDRs, Additions		$ 239		$ 239		$ 239
Leases | Commercial | Extension at Below Market Terms
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs, number | contracts		1		1
TDRs, Additions		$ 239		$ 239
Leases | Commercial | Reduction of Interest Rate
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs, number | contracts		0		0
TDRs, Additions		$ 0		$ 0
Leases | Commercial | Modification to Interest Only Payments
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs, number | contracts		0		0
TDRs, Additions		$ 0		$ 0
Leases | Commercial | Forgiveness of Debt
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs, number | contracts		0		0
TDRs, Additions		$ 0		$ 0
Office | Commercial real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs, number	1		1	1	1	1
TDRs, Additions	$ 312		$ 312	$ 59	$ 312	$ 59
Office | Commercial real estate | Extension at Below Market Terms
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs, number | contracts	1		1	1
TDRs, Additions	$ 312		$ 312	$ 59
Office | Commercial real estate | Reduction of Interest Rate
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs, number | contracts	0		0	0
TDRs, Additions	$ 0		$ 0	$ 0
Office | Commercial real estate | Modification to Interest Only Payments
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs, number | contracts	0		0	0
TDRs, Additions	$ 0		$ 0	$ 0
Office | Commercial real estate | Forgiveness of Debt
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs, number | contracts	0		0	0
TDRs, Additions	$ 0		$ 0	$ 0
Mixed use and other | Commercial real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs, number	2	1	3	1	4	1
TDRs, Additions	$ 961	$ 85	$ 1,263	$ 85	$ 1,633	$ 85
Mixed use and other | Commercial real estate | Extension at Below Market Terms
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs, number | contracts	2	1	2	1
TDRs, Additions	$ 961	$ 85	$ 961	$ 85
Mixed use and other | Commercial real estate | Reduction of Interest Rate
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs, number | contracts	0	1	0	1
TDRs, Additions	$ 0	$ 85	$ 0	$ 85
Mixed use and other | Commercial real estate | Modification to Interest Only Payments
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs, number | contracts	0	0	1	0
TDRs, Additions	$ 0	$ 0	$ 302	$ 0
Mixed use and other | Commercial real estate | Forgiveness of Debt
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs, number | contracts	0	0	0	0
TDRs, Additions	$ 0	$ 0	$ 0	$ 0