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	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017
Allowance for Loan Losses [Roll Forward]
Allowance for loan losses at beginning of period		$ 137,905	$ 122,291
Other adjustments		(181)	573
Reclassification to/from allowance for unfunded lending-related commitments		(126)	69
Charge-offs		(32,635)	(22,695)
Recoveries		12,975	7,685
Provision for credit losses		34,832	29,982
Allowance for loan losses at period end	$ 137,905	152,770	137,905
Allowance for unfunded lending-related commitments at period end	1,269	1,394	1,269
Allowance for credit losses at period end	139,174	154,164	139,174
Allowance for credit losses, Individually evaluated for impairment	8,037	11,447	8,037
Allowance for credit losses, Collectively evaluated for impairment	130,106	142,057	130,106
Loans, Individually evaluated for impairment	105,412	127,519	105,412
Loans, Collectively evaluated for impairment	21,150,978	23,280,921	21,150,978
Loans, net of unearned income	21,640,797	23,820,691	21,640,797
Loan held at fair value	33,717	93,857	33,717
Receivables Acquired with Deteriorated Credit Quality
Allowance for Loan Losses [Roll Forward]
Allowance for credit losses at period end	1,031	660	1,031
Loans, net of unearned income	350,690	318,394	350,690
Commercial
Allowance for Loan Losses [Roll Forward]
Allowance for loan losses at beginning of period		57,811	44,493
Other adjustments		(3)	16
Reclassification to/from allowance for unfunded lending-related commitments		0	500
Charge-offs		(14,532)	(5,159)
Recoveries		1,457	1,870
Provision for credit losses		23,093	16,091
Allowance for loan losses at period end	57,811	67,826	57,811
Allowance for unfunded lending-related commitments at period end	0	0	0
Allowance for credit losses at period end	57,811	67,826	57,811
Allowance for credit losses, Individually evaluated for impairment	4,464	6,558	4,464
Allowance for credit losses, Collectively evaluated for impairment	52,820	60,749	52,820
Loans, Individually evaluated for impairment	35,612	59,529	35,612
Loans, Collectively evaluated for impairment	6,742,651	7,745,482	6,742,651
Loans, net of unearned income	6,787,677	7,828,538	6,787,677
Loan held at fair value	0	0	0
Commercial | Receivables Acquired with Deteriorated Credit Quality
Allowance for Loan Losses [Roll Forward]
Allowance for credit losses at period end	527	519	527
Loans, net of unearned income	9,414	23,527	9,414
Commercial real estate
Allowance for Loan Losses [Roll Forward]
Allowance for loan losses at beginning of period		55,227	51,422
Other adjustments		(85)	(155)
Reclassification to/from allowance for unfunded lending-related commitments		(126)	(431)
Charge-offs		(1,395)	(4,236)
Recoveries		5,631	2,190
Provision for credit losses		1,015	6,437
Allowance for loan losses at period end	55,227	60,267	55,227
Allowance for unfunded lending-related commitments at period end	1,269	1,394	1,269
Allowance for credit losses at period end	56,496	61,661	56,496
Allowance for credit losses, Individually evaluated for impairment	2,177	4,287	2,177
Allowance for credit losses, Collectively evaluated for impairment	53,938	57,329	53,938
Loans, Individually evaluated for impairment	38,534	33,274	38,534
Loans, Collectively evaluated for impairment	6,414,192	6,784,834	6,414,192
Loans, net of unearned income	6,580,618	6,933,252	6,580,618
Loan held at fair value	0	0	0
Commercial real estate | Receivables Acquired with Deteriorated Credit Quality
Allowance for Loan Losses [Roll Forward]
Allowance for credit losses at period end	381	45	381
Loans, net of unearned income	127,892	115,144	127,892
Home equity
Allowance for Loan Losses [Roll Forward]
Allowance for loan losses at beginning of period		10,493	11,774
Other adjustments		(5)	167
Reclassification to/from allowance for unfunded lending-related commitments		0	0
Charge-offs		(2,245)	(3,952)
Recoveries		541	746
Provision for credit losses		(277)	1,758
Allowance for loan losses at period end	10,493	8,507	10,493
Allowance for unfunded lending-related commitments at period end	0	0	0
Allowance for credit losses at period end	10,493	8,507	10,493
Allowance for credit losses, Individually evaluated for impairment	784	282	784
Allowance for credit losses, Collectively evaluated for impairment	9,709	8,225	9,709
Loans, Individually evaluated for impairment	9,254	12,255	9,254
Loans, Collectively evaluated for impairment	653,791	540,088	653,791
Loans, net of unearned income	663,045	552,343	663,045
Loan held at fair value	0	0	0
Home equity | Receivables Acquired with Deteriorated Credit Quality
Allowance for Loan Losses [Roll Forward]
Allowance for credit losses at period end	0	0	0
Loans, net of unearned income	0	0	0
Residential real estate
Allowance for Loan Losses [Roll Forward]
Allowance for loan losses at beginning of period		6,688	5,714
Other adjustments		(25)	356
Reclassification to/from allowance for unfunded lending-related commitments		0	0
Charge-offs		(1,355)	(1,284)
Recoveries		2,075	452
Provision for credit losses		(189)	1,450
Allowance for loan losses at period end	6,688	7,194	6,688
Allowance for unfunded lending-related commitments at period end	0	0	0
Allowance for credit losses at period end	6,688	7,194	6,688
Allowance for credit losses, Individually evaluated for impairment	586	204	586
Allowance for credit losses, Collectively evaluated for impairment	5,979	6,894	5,979
Loans, Individually evaluated for impairment	21,253	22,064	21,253
Loans, Collectively evaluated for impairment	765,149	877,526	765,149
Loans, net of unearned income	832,120	1,002,464	832,120
Loan held at fair value	33,717	93,857	33,717
Residential real estate | Receivables Acquired with Deteriorated Credit Quality
Allowance for Loan Losses [Roll Forward]
Allowance for credit losses at period end	123	96	123
Loans, net of unearned income	12,001	9,017	12,001
Premium finance receivables
Allowance for Loan Losses [Roll Forward]
Allowance for loan losses at beginning of period		6,846	7,625
Other adjustments		(63)	138
Reclassification to/from allowance for unfunded lending-related commitments		0	0
Charge-offs		(12,228)	(7,335)
Recoveries		3,069	2,128
Provision for credit losses		10,091	4,290
Allowance for loan losses at period end	6,846	7,715	6,846
Allowance for unfunded lending-related commitments at period end	0	0	0
Allowance for credit losses at period end	6,846	7,715	6,846
Allowance for credit losses, Individually evaluated for impairment	0	0	0
Allowance for credit losses, Collectively evaluated for impairment	6,846	7,715	6,846
Loans, Individually evaluated for impairment	0	0	0
Loans, Collectively evaluated for impairment	6,470,355	7,215,550	6,470,355
Loan held at fair value	0	0	0
Premium finance receivables | Receivables Acquired with Deteriorated Credit Quality
Allowance for Loan Losses [Roll Forward]
Allowance for credit losses at period end	0	0	0
Loans, net of unearned income	199,269	167,903	199,269
Consumer and other
Allowance for Loan Losses [Roll Forward]
Allowance for loan losses at beginning of period		840	1,263
Other adjustments		0	51
Reclassification to/from allowance for unfunded lending-related commitments		0	0
Charge-offs		(880)	(729)
Recoveries		202	299
Provision for credit losses		1,099	(44)
Allowance for loan losses at period end	840	1,261	840
Allowance for unfunded lending-related commitments at period end	0	0	0
Allowance for credit losses at period end	840	1,261	840
Allowance for credit losses, Individually evaluated for impairment	26	116	26
Allowance for credit losses, Collectively evaluated for impairment	814	1,145	814
Loans, Individually evaluated for impairment	759	397	759
Loans, Collectively evaluated for impairment	104,840	117,441	104,840
Loans, net of unearned income	107,713	120,641	107,713
Loan held at fair value	0	0	0
Consumer and other | Receivables Acquired with Deteriorated Credit Quality
Allowance for Loan Losses [Roll Forward]
Allowance for credit losses at period end	0	0	0
Loans, net of unearned income	2,114	$ 2,803	$ 2,114
Covered Loans
Allowance for Loan Losses [Roll Forward]
Other adjustments	$ 742