Allowance for Credit Losses (Summary of the Post-Modification Balance of TDRs) (Detail) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2020 USD ($) contracts	Jun. 30, 2019 USD ($) contracts	Jun. 30, 2020 USD ($) contracts	Jun. 30, 2019 USD ($) contracts	Jun. 30, 2020 USD ($) contracts	Jun. 30, 2019 USD ($) contracts
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs, count | contracts	29	30	67	60	183	112
TDRs, balance | $	$ 9,017	$ 9,489	$ 32,814	$ 33,207	$ 53,173	$ 41,854
Extension at Below Market Terms
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs, count | contracts	26	30	52	52
TDRs, balance | $	$ 3,948	$ 9,489	$ 23,665	$ 14,483
Reduction of Interest Rate
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs, count | contracts	10	10	18	16
TDRs, balance | $	$ 1,590	$ 2,492	$ 3,297	$ 4,039
Modification to Interest Only Payments
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs, count | contracts	5	2	10	10
TDRs, balance | $	$ 5,339	$ 1,494	$ 8,802	$ 20,218
Forgiveness of Debt
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs, count | contracts	0	0	1	0
TDRs, balance | $	$ 0	$ 0	$ 432	$ 0
Commercial, industrial and other | Commercial, industrial and other
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs, count | contracts	7	5	12	14	22	17
TDRs, balance | $	$ 3,431	$ 2,455	$ 9,033	$ 21,385	$ 13,989	$ 22,067
Commercial, industrial and other | Commercial, industrial and other | Extension at Below Market Terms
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs, count | contracts	5	5	8	7
TDRs, balance | $	$ 443	$ 2,455	$ 4,759	$ 2,963
Commercial, industrial and other | Commercial, industrial and other | Reduction of Interest Rate
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs, count | contracts	0	1	0	1
TDRs, balance | $	$ 0	$ 550	$ 0	$ 550
Commercial, industrial and other | Commercial, industrial and other | Modification to Interest Only Payments
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs, count | contracts	4	2	4	9
TDRs, balance | $	$ 3,257	$ 1,494	$ 3,257	$ 19,916
Commercial, industrial and other | Commercial, industrial and other | Forgiveness of Debt
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs, count | contracts	0	0	1	0
TDRs, balance | $	$ 0	$ 0	$ 432	$ 0
Commercial real estate | Non-construction
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs, count | contracts	1	3	14	4	17	5
TDRs, balance | $	$ 2,082	$ 1,273	$ 18,135	$ 1,575	$ 23,578	$ 1,945
Commercial real estate | Non-construction | Extension at Below Market Terms
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs, count | contracts	0	3	11	3
TDRs, balance | $	$ 0	$ 1,273	$ 13,511	$ 1,273
Commercial real estate | Non-construction | Reduction of Interest Rate
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs, count | contracts	0	0	3	0
TDRs, balance | $	$ 0	$ 0	$ 921	$ 0
Commercial real estate | Non-construction | Modification to Interest Only Payments
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs, count | contracts	1	0	6	1
TDRs, balance | $	$ 2,082	$ 0	$ 5,545	$ 302
Commercial real estate | Non-construction | Forgiveness of Debt
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs, count | contracts	0	0	0	0
TDRs, balance | $	$ 0	$ 0	$ 0	$ 0
Residential real estate and other
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs, count | contracts	21	22	41	42	144	90
TDRs, balance | $	$ 3,504	$ 5,761	$ 5,646	$ 10,247	$ 15,606	$ 17,842
Residential real estate and other | Extension at Below Market Terms
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs, count | contracts	21	22	33	42
TDRs, balance | $	$ 3,505	$ 5,761	$ 5,395	$ 10,247
Residential real estate and other | Reduction of Interest Rate
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs, count | contracts	10	9	15	15
TDRs, balance | $	$ 1,590	$ 1,942	$ 2,376	$ 3,489
Residential real estate and other | Modification to Interest Only Payments
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs, count | contracts	0	0	0	0
TDRs, balance | $	$ 0	$ 0	$ 0	$ 0
Residential real estate and other | Forgiveness of Debt
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs, count | contracts	0	0	0	0
TDRs, balance | $	$ 0	$ 0	$ 0	$ 0