Loans and Allowance for Credit Losses Allowance for Loan Losses by Portfolio Segment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans and Leases Receivable, Allowance, Beginning Balance	$ 160,537	$ 169,910
Loans and leases charged off	(53,189)	(66,076)	$ (33,290)
Recoveries of loans and leases previously charged off	17,163	12,495	14,744
Net loans and leases (charged off) recovered	(36,026)	(53,581)	(18,546)
Provision for loan and lease losses	39,111	44,208
Financing receivable, allowance for credit losses, collectively evaluated for impairment	128,182	120,205
Financing receivable, allowance for credit losses, individually evaluated for impairment	35,440	40,332
Loans and Leases Receivable, Allowance, Ending Balance	163,622	160,537	169,910
Measured for impairment under FASB ASC Subtopic 450-20	16,657,279	15,975,622
Evaluated for impairment under FASB ASC Section 310-10-35	180,247	190,178
Loans and leases, net of unearned income	16,837,526	16,165,800
Change in provision allocated to commitments to lend to borrowers	6,300	2,700
Provision for credit losses	32,825	46,907	23,305
Real estate – commercial mortgage
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans and Leases Receivable, Allowance, Beginning Balance	52,889	58,793
Loans and leases charged off	(1,837)	(2,045)
Recoveries of loans and leases previously charged off	2,202	1,622
Net loans and leases (charged off) recovered	365	(423)
Provision for loan and lease losses	(7,644)	(5,481)
Financing receivable, allowance for credit losses, collectively evaluated for impairment	39,683	45,634
Financing receivable, allowance for credit losses, individually evaluated for impairment	5,927	7,255
Loans and Leases Receivable, Allowance, Ending Balance	45,610	52,889	58,793
Measured for impairment under FASB ASC Subtopic 450-20	6,654,280	6,388,212
Evaluated for impairment under FASB ASC Section 310-10-35	46,496	46,073
Loans and leases, net of unearned income	6,700,776	6,434,285
Commercial – industrial, financial and agricultural
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans and Leases Receivable, Allowance, Beginning Balance	58,868	66,280
Loans and leases charged off	(42,410)	(52,441)
Recoveries of loans and leases previously charged off	8,721	4,994
Net loans and leases (charged off) recovered	(33,689)	(47,447)
Provision for loan and lease losses	43,423	40,035
Financing receivable, allowance for credit losses, collectively evaluated for impairment	58,487	46,355
Financing receivable, allowance for credit losses, individually evaluated for impairment	10,115	12,513
Loans and Leases Receivable, Allowance, Ending Balance	68,602	58,868	66,280
Measured for impairment under FASB ASC Subtopic 450-20	4,393,402	4,349,255
Evaluated for impairment under FASB ASC Section 310-10-35	53,299	55,293
Loans and leases, net of unearned income	4,446,701	4,404,548
Real estate – home equity
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans and Leases Receivable, Allowance, Beginning Balance	18,911	18,127
Loans and leases charged off	(1,291)	(3,087)
Recoveries of loans and leases previously charged off	688	1,127
Net loans and leases (charged off) recovered	(603)	(1,960)
Provision for loan and lease losses	(564)	2,744
Financing receivable, allowance for credit losses, collectively evaluated for impairment	7,938	8,541
Financing receivable, allowance for credit losses, individually evaluated for impairment	9,806	10,370
Loans and Leases Receivable, Allowance, Ending Balance	17,744	18,911	18,127
Measured for impairment under FASB ASC Subtopic 450-20	1,292,872	1,428,764
Evaluated for impairment under FASB ASC Section 310-10-35	22,072	23,373
Loans and leases, net of unearned income	1,314,944	1,452,137
Real estate – residential mortgage
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans and Leases Receivable, Allowance, Beginning Balance	18,921	16,088
Loans and leases charged off	(1,545)	(1,574)
Recoveries of loans and leases previously charged off	989	620
Net loans and leases (charged off) recovered	(556)	(954)
Provision for loan and lease losses	1,406	3,787
Financing receivable, allowance for credit losses, collectively evaluated for impairment	10,562	9,527
Financing receivable, allowance for credit losses, individually evaluated for impairment	9,209	9,394
Loans and Leases Receivable, Allowance, Ending Balance	19,771	18,921	16,088
Measured for impairment under FASB ASC Subtopic 450-20	2,603,239	2,212,274
Evaluated for impairment under FASB ASC Section 310-10-35	38,226	38,770
Loans and leases, net of unearned income	2,641,465	2,251,044
Real estate – construction
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans and Leases Receivable, Allowance, Beginning Balance	5,061	6,620
Loans and leases charged off	(143)	(1,368)
Recoveries of loans and leases previously charged off	2,591	1,829
Net loans and leases (charged off) recovered	2,448	461
Provision for loan and lease losses	(3,066)	(2,020)
Financing receivable, allowance for credit losses, collectively evaluated for impairment	4,066	4,268
Financing receivable, allowance for credit losses, individually evaluated for impairment	377	793
Loans and Leases Receivable, Allowance, Ending Balance	4,443	5,061	6,620
Measured for impairment under FASB ASC Subtopic 450-20	967,461	909,209
Evaluated for impairment under FASB ASC Section 310-10-35	3,618	7,390
Loans and leases, net of unearned income	971,079	916,599
Consumer
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans and Leases Receivable, Allowance, Beginning Balance	3,217	2,045
Loans and leases charged off	(3,403)	(3,040)
Recoveries of loans and leases previously charged off	1,306	1,266
Net loans and leases (charged off) recovered	(2,097)	(1,774)
Provision for loan and lease losses	2,642	2,946
Financing receivable, allowance for credit losses, collectively evaluated for impairment	3,756	3,210
Financing receivable, allowance for credit losses, individually evaluated for impairment	6	7
Loans and Leases Receivable, Allowance, Ending Balance	3,762	3,217	2,045
Measured for impairment under FASB ASC Subtopic 450-20	463,156	419,175
Evaluated for impairment under FASB ASC Section 310-10-35	8	11
Loans and leases, net of unearned income	463,164	419,186
Leasing and other and overdrafts
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans and Leases Receivable, Allowance, Beginning Balance	2,670	1,957
Loans and leases charged off	(2,560)	(2,521)
Recoveries of loans and leases previously charged off	666	1,037
Net loans and leases (charged off) recovered	(1,894)	(1,484)
Provision for loan and lease losses	2,914	2,197
Financing receivable, allowance for credit losses, collectively evaluated for impairment	3,690	2,670
Financing receivable, allowance for credit losses, individually evaluated for impairment	0	0
Loans and Leases Receivable, Allowance, Ending Balance	3,690	2,670	$ 1,957
Measured for impairment under FASB ASC Subtopic 450-20	282,869	268,733
Evaluated for impairment under FASB ASC Section 310-10-35	16,528	19,268
Loans and leases, net of unearned income	$ 299,397	$ 288,001