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		6 Months Ended		12 Months Ended
	Jun. 30, 2019 USD ($) Loan contracts	Jun. 30, 2018 USD ($) Loan contracts	Jun. 30, 2019 USD ($) Loan contracts	Jun. 30, 2018 USD ($) Loan contracts	Jun. 30, 2019 USD ($) Loan	Jun. 30, 2018 USD ($) Loan
Troubled Debt Restructuring, Debtor, Subsequent Periods [Line Items]
Total, Count	30	12	60	19	112	32
Total, Balance	$ 9,489	$ 19,605	$ 33,207	$ 20,595	$ 41,854	$ 41,197
Payments in Default, Count | Loan	17	8	18	8
Payments in Default, Balance	$ 14,304	$ 4,331	$ 14,433	$ 4,331
Commercial | Commercial, industrial and other
Troubled Debt Restructuring, Debtor, Subsequent Periods [Line Items]
Total, Count	5	2	13	3	14	7
Total, Balance	$ 2,455	$ 12,827	$ 21,309	$ 12,923	$ 21,826	$ 16,603
Payments in Default, Count | Loan	5	5	5	5
Payments in Default, Balance	$ 12,014	$ 3,776	$ 12,014	$ 3,776
Commercial | Franchise
Troubled Debt Restructuring, Debtor, Subsequent Periods [Line Items]
Total, Count				2	1	5
Total, Balance				$ 5,122	$ 35	$ 21,378
Payments in Default, Count | Loan	0	0	0	0
Payments in Default, Balance	$ 0	$ 0	$ 0	$ 0
Commercial | Asset-based lending
Troubled Debt Restructuring, Debtor, Subsequent Periods [Line Items]
Total, Count		2	1		2
Total, Balance		$ 5,122	$ 76		$ 206
Payments in Default, Count | Loan	2		2
Payments in Default, Balance	$ 206		$ 206
Commercial | Leases
Troubled Debt Restructuring, Debtor, Subsequent Periods [Line Items]
Total, Count		1		1		1
Total, Balance		$ 239		$ 239		$ 239
Payments in Default, Count | Loan		0		0
Payments in Default, Balance		$ 0		$ 0
Commercial real estate | Office
Troubled Debt Restructuring, Debtor, Subsequent Periods [Line Items]
Total, Count	1		1	1	1	1
Total, Balance	$ 312		$ 312	$ 59	$ 312	$ 59
Payments in Default, Count | Loan	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]
Total, Count	2	1	3	1	4	1
Total, Balance	$ 961	$ 85	$ 1,263	$ 85	$ 1,633	$ 85
Payments in Default, Count | Loan	2	0	2	0
Payments in Default, Balance	$ 672	$ 0	$ 672	$ 0
Residential real estate and other
Troubled Debt Restructuring, Debtor, Subsequent Periods [Line Items]
Total, Count	22	6	42	11	90	17
Total, Balance	$ 5,761	$ 1,332	$ 10,247	$ 2,167	$ 17,842	$ 2,833
Payments in Default, Count | Loan	7	3	8	3
Payments in Default, Balance	$ 1,100	$ 555	$ 1,229	$ 555