Allowance for Loan Losses, Allowance for Losses on Lending-Related Commitments and Impaired Loans (Summary of Activity in the Allowance for Credit Losses by Loan Portfolio) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Allowance for Loan Losses [Roll Forward]
Allowance for loan losses at beginning of period	$ 152,770	$ 137,905
Other adjustments	(21)	(181)
Reclassification to/from allowance for unfunded lending-related commitments	(238)	(126)
Charge-offs	(59,206)	(32,635)
Recoveries	9,659	12,975
Provision for credit losses	53,864	34,832
Allowance for loan losses at period end	156,828	152,770
Allowance for unfunded lending-related commitments at period end	1,633	1,394
Allowance for credit losses at period end	158,461	154,164
Allowance for credit losses, Individually evaluated for impairment	12,336	11,447
Allowance for credit losses, Collectively evaluated for impairment	145,954	142,057
Loans, Individually evaluated for impairment	120,045	127,519
Loans, Collectively evaluated for impairment	26,254,873	23,280,921
Loans acquired with deteriorated credit quality	26,800,290	23,820,691
Loans held at fair value	132,718	93,857
Loans acquired with deteriorated credit quality
Allowance for Loan Losses [Roll Forward]
Allowance for credit losses at period end	171	660
Loans acquired with deteriorated credit quality	425,372	318,394
Commercial
Allowance for Loan Losses [Roll Forward]
Allowance for loan losses at beginning of period	67,826	57,811
Other adjustments	0	(3)
Reclassification to/from allowance for unfunded lending-related commitments	0	0
Charge-offs	(35,880)	(14,532)
Recoveries	2,845	1,457
Provision for credit losses	30,129	23,093
Allowance for loan losses at period end	64,920	67,826
Allowance for unfunded lending-related commitments at period end	0	0
Allowance for credit losses at period end	64,920	67,826
Allowance for credit losses, Individually evaluated for impairment	5,719	6,558
Allowance for credit losses, Collectively evaluated for impairment	59,171	60,749
Loans, Individually evaluated for impairment	42,130	59,529
Loans, Collectively evaluated for impairment	8,215,484	7,745,482
Loans acquired with deteriorated credit quality	8,285,920	7,828,538
Loans held at fair value	0	0
Commercial | Loans acquired with deteriorated credit quality
Allowance for Loan Losses [Roll Forward]
Allowance for credit losses at period end	30	519
Loans acquired with deteriorated credit quality	28,306	23,527
Commercial Real Estate
Allowance for Loan Losses [Roll Forward]
Allowance for loan losses at beginning of period	60,267	55,227
Other adjustments	(35)	(85)
Reclassification to/from allowance for unfunded lending-related commitments	(238)	(126)
Charge-offs	(5,402)	(1,395)
Recoveries	2,516	5,631
Provision for credit losses	9,770	1,015
Allowance for loan losses at period end	66,878	60,267
Allowance for unfunded lending-related commitments at period end	1,633	1,394
Allowance for credit losses at period end	68,511	61,661
Allowance for credit losses, Individually evaluated for impairment	5,638	4,287
Allowance for credit losses, Collectively evaluated for impairment	62,759	57,329
Loans, Individually evaluated for impairment	35,867	33,274
Loans, Collectively evaluated for impairment	7,746,969	6,784,834
Loans acquired with deteriorated credit quality	8,020,276	6,933,252
Loans held at fair value	0	0
Commercial Real Estate | Loans acquired with deteriorated credit quality
Allowance for Loan Losses [Roll Forward]
Allowance for credit losses at period end	114	45
Loans acquired with deteriorated credit quality	237,440	115,144
Home Equity
Allowance for Loan Losses [Roll Forward]
Allowance for loan losses at beginning of period	8,507	10,493
Other adjustments	(20)	(5)
Reclassification to/from allowance for unfunded lending-related commitments	0	0
Charge-offs	(3,702)	(2,245)
Recoveries	479	541
Provision for credit losses	(1,386)	(277)
Allowance for loan losses at period end	3,878	8,507
Allowance for unfunded lending-related commitments at period end	0	0
Allowance for credit losses at period end	3,878	8,507
Allowance for credit losses, Individually evaluated for impairment	450	282
Allowance for credit losses, Collectively evaluated for impairment	3,428	8,225
Loans, Individually evaluated for impairment	19,108	12,255
Loans, Collectively evaluated for impairment	493,958	540,088
Loans acquired with deteriorated credit quality	513,066	552,343
Loans held at fair value	0	0
Home Equity | Loans acquired with deteriorated credit quality
Allowance for Loan Losses [Roll Forward]
Allowance for credit losses at period end	0	0
Loans acquired with deteriorated credit quality	0	0
Residential Real Estate
Allowance for Loan Losses [Roll Forward]
Allowance for loan losses at beginning of period	7,194	6,688
Other adjustments	(15)	(25)
Reclassification to/from allowance for unfunded lending-related commitments	0	0
Charge-offs	(798)	(1,355)
Recoveries	422	2,075
Provision for credit losses	2,997	(189)
Allowance for loan losses at period end	9,800	7,194
Allowance for unfunded lending-related commitments at period end	0	0
Allowance for credit losses at period end	9,800	7,194
Allowance for credit losses, Individually evaluated for impairment	387	204
Allowance for credit losses, Collectively evaluated for impairment	9,386	6,894
Loans, Individually evaluated for impairment	22,528	22,064
Loans, Collectively evaluated for impairment	1,313,565	877,526
Loans acquired with deteriorated credit quality	1,354,221	1,002,464
Loans held at fair value	132,718	93,857
Residential Real Estate | Loans acquired with deteriorated credit quality
Allowance for Loan Losses [Roll Forward]
Allowance for credit losses at period end	27	96
Loans acquired with deteriorated credit quality	18,128	9,017
Premium Finance Receivable
Allowance for Loan Losses [Roll Forward]
Allowance for loan losses at beginning of period	7,715	6,846
Other adjustments	49	(63)
Reclassification to/from allowance for unfunded lending-related commitments	0	0
Charge-offs	(12,902)	(12,228)
Recoveries	3,203	3,069
Provision for credit losses	11,582	10,091
Allowance for loan losses at period end	9,647	7,715
Allowance for unfunded lending-related commitments at period end	0	0
Allowance for credit losses at period end	9,647	7,715
Allowance for credit losses, Individually evaluated for impairment	0	0
Allowance for credit losses, Collectively evaluated for impairment	9,647	7,715
Loans, Individually evaluated for impairment	0	0
Loans, Collectively evaluated for impairment	8,377,347	7,215,550
Loans held at fair value	0	0
Premium Finance Receivable | Loans acquired with deteriorated credit quality
Allowance for Loan Losses [Roll Forward]
Allowance for credit losses at period end	0	0
Loans acquired with deteriorated credit quality	139,282	167,903
Consumer and Other
Allowance for Loan Losses [Roll Forward]
Allowance for loan losses at beginning of period	1,261	840
Other adjustments	0	0
Reclassification to/from allowance for unfunded lending-related commitments	0	0
Charge-offs	(522)	(880)
Recoveries	194	202
Provision for credit losses	772	1,099
Allowance for loan losses at period end	1,705	1,261
Allowance for unfunded lending-related commitments at period end	0	0
Allowance for credit losses at period end	1,705	1,261
Allowance for credit losses, Individually evaluated for impairment	142	116
Allowance for credit losses, Collectively evaluated for impairment	1,563	1,145
Loans, Individually evaluated for impairment	412	397
Loans, Collectively evaluated for impairment	107,550	117,441
Loans acquired with deteriorated credit quality	110,178	120,641
Loans held at fair value	0	0
Consumer and Other | Loans acquired with deteriorated credit quality
Allowance for Loan Losses [Roll Forward]
Allowance for credit losses at period end	0	0
Loans acquired with deteriorated credit quality	$ 2,216	$ 2,803