Allowance for Loan Losses, Allowance for Losses on Lending-Related Commitments and Impaired Loans (Summary of Impaired Loans by Loan Class) (Detail) - USD ($) $ in Thousands	6 Months Ended		12 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, with Related Allowance, Recorded Investment	$ 60,122	$ 39,956	$ 60,219
Impaired Financing Receivable, Related Allowance	15,200	8,541	11,437
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	77,165	80,346	67,050
Total impaired loans	137,287	120,302	127,269
Impaired Financing Receivable, Unpaid Principal Balance	168,239	135,812	139,246
Impaired Financing Receivable, Average Recorded Investment	158,887	124,979	133,481
Impaired Financing Receivable, Interest Income Recognized	5,210	3,220	7,347
Commercial | Commercial, industrial and other
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, with Related Allowance, Recorded Investment	27,818	8,942	16,703
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	35,935	9,022	17,029
Impaired Financing Receivable, Related Allowance	10,105	2,948	4,866
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment	34,672	9,458	17,868
Impaired Financing Receivable, with Related Allowance, Interest Income Recognized	1,401	278	1,181
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	21,498	18,260	18,314
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	24,238	19,731	21,501
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment	22,124	18,717	20,547
Impaired Financing Receivable, with No Related Allowance, Interest Income Recognized	981	211	1,143
Commercial | Franchise
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, with Related Allowance, Recorded Investment	178	2,399	16,021
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	178	2,399	16,256
Impaired Financing Receivable, Related Allowance	178	1,208	1,375
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment	187	2,415	16,221
Impaired Financing Receivable, with Related Allowance, Interest Income Recognized	5	68	909
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	10,898	21,417	5,152
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	19,206	21,418	5,154
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment	18,884	21,740	5,320
Impaired Financing Receivable, with No Related Allowance, Interest Income Recognized	665	640	403
Commercial | Asset-based lending
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, with Related Allowance, Recorded Investment	300	469	557
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	300	469	557
Impaired Financing Receivable, Related Allowance	300	225	317
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment	322	529	689
Impaired Financing Receivable, with Related Allowance, Interest Income Recognized	13	20	50
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	398	1,689	207
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	2,093	2,494	601
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment	1,400	2,432	569
Impaired Financing Receivable, with No Related Allowance, Interest Income Recognized	61	73	51
Commercial | Leases
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, with Related Allowance, Recorded Investment	1,693	2,062	1,730
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	1,693	2,091	1,730
Impaired Financing Receivable, Related Allowance	5	25	0
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment	1,736	2,126	1,812
Impaired Financing Receivable, with Related Allowance, Interest Income Recognized	44	54	91
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	745	710	845
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	782	710	879
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment	786	738	936
Impaired Financing Receivable, with No Related Allowance, Interest Income Recognized	25	22	56
Commercial real estate | Construction
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, with Related Allowance, Recorded Investment	0	1,554	1,554
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	0	1,554	1,554
Impaired Financing Receivable, Related Allowance	0	390	550
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment	0	1,554	1,554
Impaired Financing Receivable, with Related Allowance, Interest Income Recognized	0	36	76
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	1,030	1,320	1,117
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	1,554	3,663	1,117
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment	1,205	2,606	1,218
Impaired Financing Receivable, with No Related Allowance, Interest Income Recognized	42	96	52
Commercial real estate | Land
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, with Related Allowance, Recorded Investment	1,208	1,500	0
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	1,208	1,500	0
Impaired Financing Receivable, Related Allowance	215	1	0
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment	1,208	1,533	0
Impaired Financing Receivable, with Related Allowance, Interest Income Recognized	33	34	0
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	2,074	2,375	3,396
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	2,197	2,482	3,491
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment	2,098	2,382	3,751
Impaired Financing Receivable, with No Related Allowance, Interest Income Recognized	61	65	198
Commercial real estate | Office
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, with Related Allowance, Recorded Investment	8,063	1,002	573
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	8,152	1,604	638
Impaired Financing Receivable, Related Allowance	3,446	65	21
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment	8,151	1,010	587
Impaired Financing Receivable, with Related Allowance, Interest Income Recognized	188	37	25
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	1,471	1,380	3,629
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	1,486	2,075	3,642
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment	1,458	1,387	3,651
Impaired Financing Receivable, with No Related Allowance, Interest Income Recognized	43	58	184
Commercial real estate | Industrial
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, with Related Allowance, Recorded Investment	0	0	0
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	0	0	0
Impaired Financing Receivable, Related Allowance	0	0	0
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment	0	0	0
Impaired Financing Receivable, with Related Allowance, Interest Income Recognized	0	0	0
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	386	240	322
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	521	363	450
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment	398	251	363
Impaired Financing Receivable, with No Related Allowance, Interest Income Recognized	16	10	30
Commercial real estate | Retail
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, with Related Allowance, Recorded Investment	5,062	15,252	14,633
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	5,062	15,441	14,633
Impaired Financing Receivable, Related Allowance	38	2,497	3,413
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment	5,094	15,267	14,694
Impaired Financing Receivable, with Related Allowance, Interest Income Recognized	113	344	676
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	7,276	1,845	1,592
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	10,756	2,058	1,945
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment	8,483	1,875	1,699
Impaired Financing Receivable, with No Related Allowance, Interest Income Recognized	286	75	110
Commercial real estate | Multi-family
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, with Related Allowance, Recorded Investment	1,177	1,205	0
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	1,177	1,205	0
Impaired Financing Receivable, Related Allowance	27	14	0
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment	1,182	1,214	0
Impaired Financing Receivable, with Related Allowance, Interest Income Recognized	25	22	0
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	296	342	1,498
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	399	477	1,595
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment	302	358	1,529
Impaired Financing Receivable, with No Related Allowance, Interest Income Recognized	6	8	55
Commercial real estate | Mixed use and other
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, with Related Allowance, Recorded Investment	985	1,510	1,188
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	1,026	1,722	1,221
Impaired Financing Receivable, Related Allowance	247	210	293
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment	998	1,822	1,354
Impaired Financing Receivable, with Related Allowance, Interest Income Recognized	24	53	66
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	4,494	4,755	3,522
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	4,751	5,366	3,836
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment	4,594	5,006	3,611
Impaired Financing Receivable, with No Related Allowance, Interest Income Recognized	125	165	227
Home equity
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, with Related Allowance, Recorded Investment	7,518	1,305	3,133
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	7,866	1,403	3,470
Impaired Financing Receivable, Related Allowance	209	732	282
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment	7,571	1,315	3,165
Impaired Financing Receivable, with Related Allowance, Interest Income Recognized	143	32	131
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	10,785	8,612	9,122
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	12,540	12,977	12,383
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment	10,907	8,818	9,323
Impaired Financing Receivable, with No Related Allowance, Interest Income Recognized	308	324	564
Residential real estate
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, with Related Allowance, Recorded Investment	6,011	2,450	4,011
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	6,288	2,702	4,263
Impaired Financing Receivable, Related Allowance	321	106	204
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment	6,047	2,472	4,056
Impaired Financing Receivable, with Related Allowance, Interest Income Recognized	110	59	159
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	15,652	17,104	18,053
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	18,390	20,137	20,765
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment	18,777	17,341	18,552
Impaired Financing Receivable, with No Related Allowance, Interest Income Recognized	482	417	883
Consumer and other
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, with Related Allowance, Recorded Investment	109	306	116
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	126	328	129
Impaired Financing Receivable, Related Allowance	109	120	116
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment	112	309	119
Impaired Financing Receivable, with Related Allowance, Interest Income Recognized	3	9	7
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	162	297	281
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	315	421	407
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment	191	304	293
Impaired Financing Receivable, with No Related Allowance, Interest Income Recognized	$ 7	$ 10	$ 20