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, 2018	Jun. 30, 2017	Dec. 31, 2017
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, with Related Allowance, Recorded Investment	$ 39,956	$ 29,037	$ 36,084
Impaired Financing Receivable, Related Allowance	8,541	5,633	8,023
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	80,346	50,281	69,004
Total impaired loans	120,302	79,318	105,088
Impaired Financing Receivable, Unpaid Principal Balance	135,812	90,876	127,566
Impaired Financing Receivable, Average Recorded Investment	124,979	84,874	115,261
Impaired Financing Receivable, Interest Income Recognized	3,220	2,261	6,298
Commercial
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, with Related Allowance, Recorded Investment		0
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance		0
Impaired Financing Receivable, Related Allowance		0
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment		0
Impaired Financing Receivable, with Related Allowance, Interest Income Recognized		0
Impaired Financing Receivable, with No Related Allowance, Recorded Investment		0
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance		0
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment		0
Impaired Financing Receivable, with No Related Allowance, Interest Income Recognized		0
Commercial | Commercial, industrial and other
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, with Related Allowance, Recorded Investment	8,942	2,969	6,233
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	9,022	3,006	7,323
Impaired Financing Receivable, Related Allowance	2,948	1,499	3,951
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment	9,458	3,061	7,220
Impaired Financing Receivable, with Related Allowance, Interest Income Recognized	278	83	452
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	18,260	6,815	8,460
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	19,731	7,785	12,259
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment	18,717	7,285	10,170
Impaired Financing Receivable, with No Related Allowance, Interest Income Recognized	211	213	683
Commercial | Franchise
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, with Related Allowance, Recorded Investment	2,399		0
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	2,399		0
Impaired Financing Receivable, Related Allowance	1,208		0
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment	2,415		0
Impaired Financing Receivable, with Related Allowance, Interest Income Recognized	68		0
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	21,417		16,256
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	21,418		16,256
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment	21,740		17,089
Impaired Financing Receivable, with No Related Allowance, Interest Income Recognized	640		780
Commercial | Asset-based lending
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, with Related Allowance, Recorded Investment	469	511	948
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	469	512	949
Impaired Financing Receivable, Related Allowance	225	293	355
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment	529	704	1,302
Impaired Financing Receivable, with Related Allowance, Interest Income Recognized	20	21	72
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	1,689	425	602
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	2,494	425	602
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment	2,432	764	688
Impaired Financing Receivable, with No Related Allowance, Interest Income Recognized	73	16	40
Commercial | Leases
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, with Related Allowance, Recorded Investment	2,062	2,504	2,331
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	2,091	2,508	2,337
Impaired Financing Receivable, Related Allowance	25	235	158
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment	2,126	2,578	2,463
Impaired Financing Receivable, with Related Allowance, Interest Income Recognized	54	62	117
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	710	852	782
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	710	852	782
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment	738	879	845
Impaired Financing Receivable, with No Related Allowance, Interest Income Recognized	22	26	49
Commercial real estate | Construction
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, with Related Allowance, Recorded Investment	1,554	7,632	3,097
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	1,554	7,632	3,897
Impaired Financing Receivable, Related Allowance	390	957	403
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment	1,554	7,665	3,690
Impaired Financing Receivable, with Related Allowance, Interest Income Recognized	36	165	197
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	1,320	1,504	1,367
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	3,663	1,504	1,678
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment	2,606	1,534	1,555
Impaired Financing Receivable, with No Related Allowance, Interest Income Recognized	96	33	84
Commercial real estate | Land
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, with Related Allowance, Recorded Investment	1,500	1,750	0
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	1,500	1,750	0
Impaired Financing Receivable, Related Allowance	1	7	0
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment	1,533	1,750	0
Impaired Financing Receivable, with Related Allowance, Interest Income Recognized	34	32	0
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	2,375	2,375	3,961
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	2,482	2,472	4,192
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment	2,382	2,380	4,129
Impaired Financing Receivable, with No Related Allowance, Interest Income Recognized	65	56	182
Commercial real estate | Office
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, with Related Allowance, Recorded Investment	1,002	1,314	471
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	1,604	1,418	471
Impaired Financing Receivable, Related Allowance	65	32	5
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment	1,010	1,318	481
Impaired Financing Receivable, with Related Allowance, Interest Income Recognized	37	44	24
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	1,380	3,973	2,438
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	2,075	5,074	6,140
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment	1,387	4,076	3,484
Impaired Financing Receivable, with No Related Allowance, Interest Income Recognized	58	131	330
Commercial real estate | Industrial
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, with Related Allowance, Recorded Investment	0	0	408
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	0	0	408
Impaired Financing Receivable, Related Allowance	0	0	40
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment	0	0	414
Impaired Financing Receivable, with Related Allowance, Interest Income Recognized	0	0	25
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	240	2,193	403
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	363	3,622	2,010
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment	251	4,328	1,849
Impaired Financing Receivable, with No Related Allowance, Interest Income Recognized	10	190	174
Commercial real estate | Retail
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, with Related Allowance, Recorded Investment	15,252	1,582	15,599
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	15,441	1,631	15,657
Impaired Financing Receivable, Related Allowance	2,497	130	1,336
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment	15,267	1,596	15,736
Impaired Financing Receivable, with Related Allowance, Interest Income Recognized	344	40	624
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	1,845	1,188	2,393
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	2,058	1,273	3,538
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment	1,875	1,188	2,486
Impaired Financing Receivable, with No Related Allowance, Interest Income Recognized	75	51	221
Commercial real estate | Multi-family
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, with Related Allowance, Recorded Investment	1,205	1,513	0
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	1,205	1,513	0
Impaired Financing Receivable, Related Allowance	14	27	0
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment	1,214	1,518	0
Impaired Financing Receivable, with Related Allowance, Interest Income Recognized	22	28	0
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	342	89	1,231
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	477	174	2,078
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment	358	89	1,246
Impaired Financing Receivable, with No Related Allowance, Interest Income Recognized	8	4	76
Commercial real estate | Mixed use and other
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, with Related Allowance, Recorded Investment	1,510	1,455	1,567
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	1,722	1,531	1,586
Impaired Financing Receivable, Related Allowance	210	302	379
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment	1,822	1,478	1,599
Impaired Financing Receivable, with Related Allowance, Interest Income Recognized	53	35	77
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	4,755	7,761	5,275
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	5,366	9,299	6,731
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment	5,006	8,494	5,559
Impaired Financing Receivable, with No Related Allowance, Interest Income Recognized	165	239	351
Home equity
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, with Related Allowance, Recorded Investment	1,305	1,901	1,606
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	1,403	1,950	1,869
Impaired Financing Receivable, Related Allowance	732	1,296	784
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment	1,315	1,920	1,626
Impaired Financing Receivable, with Related Allowance, Interest Income Recognized	32	35	81
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	8,612	7,732	7,648
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	12,977	11,260	11,648
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment	8,818	8,906	9,114
Impaired Financing Receivable, with No Related Allowance, Interest Income Recognized	324	258	603
Residential real estate
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, with Related Allowance, Recorded Investment	2,450	5,815	3,798
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	2,702	6,090	3,910
Impaired Financing Receivable, Related Allowance	106	764	586
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment	2,472	5,731	3,790
Impaired Financing Receivable, with Related Allowance, Interest Income Recognized	59	118	146
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	17,104	15,044	17,455
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	20,137	17,068	20,327
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment	17,341	15,203	17,926
Impaired Financing Receivable, with No Related Allowance, Interest Income Recognized	417	368	860
Consumer and other
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, with Related Allowance, Recorded Investment	306	91	26
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	328	93	28
Impaired Financing Receivable, Related Allowance	120	91	26
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment	309	96	27
Impaired Financing Receivable, with Related Allowance, Interest Income Recognized	9	2	2
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	297	330	733
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	421	434	890
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment	304	333	773
Impaired Financing Receivable, with No Related Allowance, Interest Income Recognized	$ 10	$ 11	$ 48