Allowance for Loan Losses, Allowance for Losses on Lending-Related Commitments and Impaired Loans (Schedule of Aging of the Company's Loan Portfolio) (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018
Financing Receivable, Past Due [Line Items]
Nonaccrual	$ 103,619	$ 105,326	$ 114,844
90+ days and still accruing	19,347	18,872	23,260
Current	25,401,935	23,526,168	22,834,140
Total Loans	25,710,171	23,820,691	23,123,951
60-89 days past due
Financing Receivable, Past Due [Line Items]
Past Due	51,113	34,176	42,344
30-59 days past due
Financing Receivable, Past Due [Line Items]
Past Due	134,157	136,149	109,363
Commercial
Financing Receivable, Past Due [Line Items]
Nonaccrual	43,931	50,984	58,587
90+ days and still accruing	382	3,313	8,494
Current	8,086,942	7,737,729	7,375,123
Total Loans	8,195,602	7,828,538	7,473,958
Commercial | 60-89 days past due
Financing Receivable, Past Due [Line Items]
Past Due	12,860	1,651	6,140
Commercial | 30-59 days past due
Financing Receivable, Past Due [Line Items]
Past Due	51,487	34,861	25,614
Commercial | Commercial, industrial and other
Financing Receivable, Past Due [Line Items]
Nonaccrual	34,397	34,298	41,322
90+ days and still accruing	0	0	0
Current	5,096,879	5,062,729	4,745,178
Total Loans	5,150,567	5,120,096	4,805,486
Commercial | Commercial, industrial and other | 60-89 days past due
Financing Receivable, Past Due [Line Items]
Past Due	2,296	1,451	2,535
Commercial | Commercial, industrial and other | 30-59 days past due
Financing Receivable, Past Due [Line Items]
Past Due	16,995	21,618	16,451
Commercial | Franchise
Financing Receivable, Past Due [Line Items]
Nonaccrual	3,752	16,051	16,351
90+ days and still accruing	0	0	5,122
Current	903,695	924,190	915,817
Total Loans	914,774	948,979	937,290
Commercial | Franchise | 60-89 days past due
Financing Receivable, Past Due [Line Items]
Past Due	0	0	0
Commercial | Franchise | 30-59 days past due
Financing Receivable, Past Due [Line Items]
Past Due	7,327	8,738	0
Commercial | Mortgage warehouse lines of credit
Financing Receivable, Past Due [Line Items]
Nonaccrual	0	0	0
90+ days and still accruing	0	0	0
Current	311,501	144,199	168,860
Total Loans	314,697	144,199	171,860
Commercial | Mortgage warehouse lines of credit | 60-89 days past due
Financing Receivable, Past Due [Line Items]
Past Due	0	0	3,000
Commercial | Mortgage warehouse lines of credit | 30-59 days past due
Financing Receivable, Past Due [Line Items]
Past Due	3,196	0	0
Commercial | Asset-based lending
Financing Receivable, Past Due [Line Items]
Nonaccrual	5,782	635	910
90+ days and still accruing	0	0	0
Current	1,007,197	1,022,065	1,023,268
Total Loans	1,045,869	1,026,056	1,033,851
Commercial | Asset-based lending | 60-89 days past due
Financing Receivable, Past Due [Line Items]
Past Due	9,521	200	590
Commercial | Asset-based lending | 30-59 days past due
Financing Receivable, Past Due [Line Items]
Past Due	23,369	3,156	9,083
Commercial | Leases
Financing Receivable, Past Due [Line Items]
Nonaccrual	0	0	4
90+ days and still accruing	0	0	0
Current	753,770	564,430	509,591
Total Loans	754,163	565,680	509,675
Commercial | Leases | 60-89 days past due
Financing Receivable, Past Due [Line Items]
Past Due	0	0	0
Commercial | Leases | 30-59 days past due
Financing Receivable, Past Due [Line Items]
Past Due	393	1,250	80
Commercial | PCI - commercial
Financing Receivable, Past Due [Line Items]
Nonaccrual	0	0	0
90+ days and still accruing	382	3,313	3,372
Current	13,900	20,116	12,409
Total Loans	15,532	23,528	15,796
Commercial | PCI - commercial | 60-89 days past due
Financing Receivable, Past Due [Line Items]
Past Due	1,043	0	15
Commercial | PCI - commercial | 30-59 days past due
Financing Receivable, Past Due [Line Items]
Past Due	207	99	0
Commercial real estate
Financing Receivable, Past Due [Line Items]
Nonaccrual	21,557	19,129	17,515
90+ days and still accruing	4,992	6,241	5,578
Current	7,379,391	6,845,490	6,652,557
Total Loans	7,448,667	6,933,252	6,746,774
Commercial real estate | 60-89 days past due
Financing Receivable, Past Due [Line Items]
Past Due	9,629	10,826	27,040
Commercial real estate | 30-59 days past due
Financing Receivable, Past Due [Line Items]
Past Due	33,098	51,566	44,084
Commercial real estate | Construction
Financing Receivable, Past Due [Line Items]
Nonaccrual	1,030	1,554	1,554
90+ days and still accruing	0	0	0
Current	847,442	749,846	778,725
Total Loans	850,575	760,824	798,330
Commercial real estate | Construction | 60-89 days past due
Financing Receivable, Past Due [Line Items]
Past Due	0	0	1,823
Commercial real estate | Construction | 30-59 days past due
Financing Receivable, Past Due [Line Items]
Past Due	2,103	9,424	16,228
Commercial real estate | Land
Financing Receivable, Past Due [Line Items]
Nonaccrual	994	107	228
90+ days and still accruing	0	0	0
Current	169,357	141,097	118,411
Total Loans	175,386	141,481	119,004
Commercial real estate | Land | 60-89 days past due
Financing Receivable, Past Due [Line Items]
Past Due	88	170	365
Commercial real estate | Land | 30-59 days past due
Financing Receivable, Past Due [Line Items]
Past Due	4,947	107	0
Commercial real estate | Office
Financing Receivable, Past Due [Line Items]
Nonaccrual	8,158	3,629	1,532
90+ days and still accruing	0	0	0
Current	986,470	929,739	932,166
Total Loans	996,931	939,322	940,777
Commercial real estate | Office | 60-89 days past due
Financing Receivable, Past Due [Line Items]
Past Due	158	877	4,058
Commercial real estate | Office | 30-59 days past due
Financing Receivable, Past Due [Line Items]
Past Due	2,145	5,077	3,021
Commercial real estate | Industrial
Financing Receivable, Past Due [Line Items]
Nonaccrual	100	285	178
90+ days and still accruing	0	0	0
Current	1,007,669	885,367	885,486
Total Loans	1,009,680	902,248	885,931
Commercial real estate | Industrial | 60-89 days past due
Financing Receivable, Past Due [Line Items]
Past Due	950	0	122
Commercial real estate | Industrial | 30-59 days past due
Financing Receivable, Past Due [Line Items]
Past Due	961	16,596	145
Commercial real estate | Retail
Financing Receivable, Past Due [Line Items]
Nonaccrual	7,174	10,753	10,586
90+ days and still accruing	0	0	0
Current	991,627	878,106	861,901
Total Loans	1,004,720	892,478	887,702
Commercial real estate | Retail | 60-89 days past due
Financing Receivable, Past Due [Line Items]
Past Due	2,235	1,890	4,570
Commercial real estate | Retail | 30-59 days past due
Financing Receivable, Past Due [Line Items]
Past Due	3,684	1,729	10,645
Commercial real estate | Multi-family
Financing Receivable, Past Due [Line Items]
Nonaccrual	690	311	318
90+ days and still accruing	0	0	0
Current	1,287,797	970,597	922,413
Total Loans	1,291,825	976,560	923,893
Commercial real estate | Multi-family | 60-89 days past due
Financing Receivable, Past Due [Line Items]
Past Due	1,073	77	0
Commercial real estate | Multi-family | 30-59 days past due
Financing Receivable, Past Due [Line Items]
Past Due	2,265	5,575	1,162
Commercial real estate | Mixed use and other
Financing Receivable, Past Due [Line Items]
Nonaccrual	3,411	2,490	3,119
90+ days and still accruing	0	0	0
Current	1,987,844	2,192,105	2,062,179
Total Loans	2,002,267	2,205,195	2,086,455
Commercial real estate | Mixed use and other | 60-89 days past due
Financing Receivable, Past Due [Line Items]
Past Due	928	1,617	9,654
Commercial real estate | Mixed use and other | 30-59 days past due
Financing Receivable, Past Due [Line Items]
Past Due	10,084	8,983	11,503
Commercial real estate | PCI - commercial real estate
Financing Receivable, Past Due [Line Items]
Nonaccrual	0	0	0
90+ days and still accruing	4,992	6,241	5,578
Current	101,185	98,633	91,276
Total Loans	117,283	115,144	104,682
Commercial real estate | PCI - commercial real estate | 60-89 days past due
Financing Receivable, Past Due [Line Items]
Past Due	4,197	6,195	6,448
Commercial real estate | PCI - commercial real estate | 30-59 days past due
Financing Receivable, Past Due [Line Items]
Past Due	6,909	4,075	1,380
Home equity
Financing Receivable, Past Due [Line Items]
Nonaccrual	7,920	7,147	8,523
90+ days and still accruing	0	0	0
Current	501,188	541,960	565,768
Total Loans	512,303	552,343	578,844
Home equity | 60-89 days past due
Financing Receivable, Past Due [Line Items]
Past Due	95	131	1,075
Home equity | 30-59 days past due
Financing Receivable, Past Due [Line Items]
Past Due	3,100	3,105	3,478
Residential real estate
Financing Receivable, Past Due [Line Items]
Nonaccrual	13,447	16,383	16,062
90+ days and still accruing	3,244	1,292	1,865
Current	1,198,674	976,926	904,006
Total Loans	1,218,666	1,002,464	924,250
Residential real estate | 60-89 days past due
Financing Receivable, Past Due [Line Items]
Past Due	1,868	1,692	1,714
Residential real estate | 30-59 days past due
Financing Receivable, Past Due [Line Items]
Past Due	1,433	6,171	603
Premium finance receivables | Commercial insurance loans
Financing Receivable, Past Due [Line Items]
Nonaccrual	15,950	11,335	13,802
90+ days and still accruing	10,612	7,799	7,028
Current	3,397,563	2,796,058	2,845,313
Total Loans	3,449,950	2,841,659	2,885,327
Premium finance receivables | Commercial insurance loans | 60-89 days past due
Financing Receivable, Past Due [Line Items]
Past Due	8,853	11,382	5,945
Premium finance receivables | Commercial insurance loans | 30-59 days past due
Financing Receivable, Past Due [Line Items]
Past Due	16,972	15,085	13,239
Premium finance receivables | Life insurance loans
Financing Receivable, Past Due [Line Items]
Nonaccrual	590	0	0
90+ days and still accruing	0	0	0
Current	4,608,450	4,340,856	4,203,465
Total Loans	4,654,588	4,373,891	4,225,481
Premium finance receivables | Life insurance loans | 60-89 days past due
Financing Receivable, Past Due [Line Items]
Past Due	17,753	8,407	0
Premium finance receivables | Life insurance loans | 30-59 days past due
Financing Receivable, Past Due [Line Items]
Past Due	27,795	24,628	22,016
Premium finance receivables | PCI - life insurance loans
Financing Receivable, Past Due [Line Items]
Nonaccrual	0	0	0
90+ days and still accruing	0	0	0
Current	140,908	167,903	173,490
Total Loans	140,908	167,903	173,490
Premium finance receivables | PCI - life insurance loans | 60-89 days past due
Financing Receivable, Past Due [Line Items]
Past Due	0	0	0
Premium finance receivables | PCI - life insurance loans | 30-59 days past due
Financing Receivable, Past Due [Line Items]
Past Due	0	0	0
Consumer and other
Financing Receivable, Past Due [Line Items]
Nonaccrual	224	348	355
90+ days and still accruing	117	227	295
Current	88,819	119,246	114,418
Total Loans	89,487	120,641	115,827
Consumer and other | 60-89 days past due
Financing Receivable, Past Due [Line Items]
Past Due	55	87	430
Consumer and other | 30-59 days past due
Financing Receivable, Past Due [Line Items]
Past Due	$ 272	$ 733	$ 329