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		9 Months Ended		12 Months Ended
	Sep. 30, 2019 USD ($) contracts	Sep. 30, 2018 USD ($) contracts	Sep. 30, 2019 USD ($) contracts	Sep. 30, 2018 USD ($) contracts	Sep. 30, 2019 USD ($) contracts	Sep. 30, 2018 USD ($) contracts
Troubled Debt Restructuring, Debtor, Subsequent Periods [Line Items]
TDRs, count | contracts	68	22	127	41	157	49
TDRs, balance | $	$ 13,597	$ 4,233	$ 46,804	$ 24,828	$ 51,219	$ 43,767
Payments in default, count | contracts	18	13	23	13
Payments in default, balance | $	$ 6,545	$ 9,111	$ 18,692	$ 9,111
Commercial | Commercial, industrial and other
Troubled Debt Restructuring, Debtor, Subsequent Periods [Line Items]
TDRs, count | contracts	5	1	18	4	18	5
TDRs, balance | $	$ 3,526	$ 519	$ 24,835	$ 13,442	$ 24,835	$ 15,714
Payments in default, count | contracts	3	3	6	3
Payments in default, balance | $	$ 1,743	$ 2,447	$ 13,348	$ 2,447
Commercial | Franchise
Troubled Debt Restructuring, Debtor, Subsequent Periods [Line Items]
TDRs, count | contracts		1		3		6
TDRs, balance | $		$ 35		$ 5,157		$ 21,413
Payments in default, count | contracts		2		2
Payments in default, balance | $		$ 5,122		$ 5,122
Commercial | Asset-based lending
Troubled Debt Restructuring, Debtor, Subsequent Periods [Line Items]
TDRs, count | contracts			1		2
TDRs, balance | $			$ 76		$ 206
Payments in default, count | contracts	2		2
Payments in default, balance | $	$ 206		$ 206
Commercial | Leases
Troubled Debt Restructuring, Debtor, Subsequent Periods [Line Items]
TDRs, count | contracts		0		1		1
TDRs, balance | $		$ 0		$ 239		$ 239
Payments in default, count | contracts		0		0
Payments in default, balance | $		$ 0		$ 0
Commercial real estate | Office
Troubled Debt Restructuring, Debtor, Subsequent Periods [Line Items]
TDRs, count | contracts	1		2	1	2	1
TDRs, balance | $	$ 5,070		$ 5,382	$ 59	$ 5,382	$ 59
Payments in default, count | contracts	1	0	1	0
Payments in default, balance | $	$ 312	$ 0	$ 312	$ 0
Commercial real estate | Mixed use and other
Troubled Debt Restructuring, Debtor, Subsequent Periods [Line Items]
TDRs, count | contracts	2	0	4	1	5	1
TDRs, balance | $	$ 122	$ 0	$ 1,385	$ 85	$ 1,755	$ 85
Payments in default, count | contracts	1	1	2	1
Payments in default, balance | $	$ 370	$ 85	$ 672	$ 85
Residential real estate and other
Troubled Debt Restructuring, Debtor, Subsequent Periods [Line Items]
TDRs, count | contracts	60	20	102	31	130	35
TDRs, balance | $	$ 4,879	$ 3,679	$ 15,126	$ 5,846	$ 19,041	$ 6,257
Payments in default, count | contracts	11	7	12	7
Payments in default, balance | $	$ 3,914	$ 1,457	$ 4,154	$ 1,457