Allowance for Credit Losses (Loan Portfolio by Credit Quality Indicator) (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020	Sep. 30, 2020
Financing Receivable, Credit Quality Indicator [Line Items]
2021	$ 9,593,469
2020	4,641,356
2019	3,465,980
2018	2,582,554
2017	2,244,073
Prior	6,726,820
Revolving	3,984,335
Revolving to Term	25,456
Total Loans	33,264,043	$ 32,079,073	$ 32,135,555
Loans with COVID-19 related modifications	37,500
Commercial, industrial and other
Financing Receivable, Credit Quality Indicator [Line Items]
2021	1,917,957
2020	1,629,151
2019	1,099,593
2018	791,739
2017	523,826
Prior	689,653
Revolving	3,437,168
Revolving to Term	16,897
Total Loans	10,105,984
Commercial PPP loans
Financing Receivable, Credit Quality Indicator [Line Items]
2021	909,139
2020	172,849
2019	0
2018	0
2017	0
Prior	0
Revolving	0
Revolving to Term	0
Total Loans	1,081,988
Construction and development
Financing Receivable, Credit Quality Indicator [Line Items]
2021	214,926
2020	412,094
2019	339,114
2018	151,843
2017	105,319
Prior	93,194
Revolving	24,537
Revolving to Term	2,688
Total Loans	1,343,715
Non-construction
Financing Receivable, Credit Quality Indicator [Line Items]
2021	1,042,866
2020	1,228,255
2019	1,082,005
2018	878,937
2017	818,658
Prior	2,300,881
Revolving	185,418
Revolving to Term	4,979
Total Loans	7,541,999
Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
2021	8
2020	0
2019	0
2018	231
2017	176
Prior	19,799
Revolving	326,556
Revolving to Term	892
Total Loans	347,662	425,263	446,274
Residential real estate
Financing Receivable, Credit Quality Indicator [Line Items]
2021	675,006
2020	303,236
2019	196,459
2018	83,572
2017	96,049
Prior	193,414
Revolving	0
Revolving to Term	0
Total Loans	1,547,736	1,259,598	1,384,810
Premium finance receivables - commercial
Financing Receivable, Credit Quality Indicator [Line Items]
2021	4,490,480
2020	111,704
2019	13,257
2018	1,486
2017	50
Prior	0
Revolving	0
Revolving to Term	0
Total Loans	4,616,977
Premium finance receivables - life
Financing Receivable, Credit Quality Indicator [Line Items]
2021	340,318
2020	782,936
2019	734,280
2018	673,416
2017	699,831
Prior	3,424,672
Revolving	0
Revolving to Term	0
Total Loans	6,655,453
Consumer and other
Financing Receivable, Credit Quality Indicator [Line Items]
2021	2,769
2020	1,131
2019	1,272
2018	1,330
2017	164
Prior	5,207
Revolving	10,656
Revolving to Term	0
Total Loans	22,529	$ 32,188	$ 55,354
Pass
Financing Receivable, Credit Quality Indicator [Line Items]
2021	9,508,713
2020	4,548,827
2019	3,271,496
2018	2,395,263
2017	2,100,615
Prior	6,360,819
Revolving	3,841,713
Revolving to Term	17,903
Total Loans	32,045,349
Pass | Commercial, industrial and other
Financing Receivable, Credit Quality Indicator [Line Items]
2021	1,876,457
2020	1,567,410
2019	1,005,156
2018	711,177
2017	481,140
Prior	620,202
Revolving	3,301,541
Revolving to Term	10,236
Total Loans	9,573,319
Pass | Commercial PPP loans
Financing Receivable, Credit Quality Indicator [Line Items]
2021	909,139
2020	171,213
2019	0
2018	0
2017	0
Prior	0
Revolving	0
Revolving to Term	0
Total Loans	1,080,352
Pass | Construction and development
Financing Receivable, Credit Quality Indicator [Line Items]
2021	214,644
2020	403,619
2019	326,654
2018	131,600
2017	79,752
Prior	88,452
Revolving	24,382
Revolving to Term	2,688
Total Loans	1,271,791
Pass | Non-construction
Financing Receivable, Credit Quality Indicator [Line Items]
2021	1,039,349
2020	1,215,988
2019	997,258
2018	796,708
2017	752,951
Prior	2,053,618
Revolving	185,418
Revolving to Term	4,979
Total Loans	7,046,269
Pass | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
2021	8
2020	0
2019	0
2018	0
2017	28
Prior	7,050
Revolving	319,725
Revolving to Term	0
Total Loans	326,811
Pass | Residential real estate
Financing Receivable, Credit Quality Indicator [Line Items]
2021	672,993
2020	299,739
2019	193,715
2018	79,703
2017	87,361
Prior	162,230
Revolving	0
Revolving to Term	0
Total Loans	1,495,741
Pass | Premium finance receivables - commercial
Financing Receivable, Credit Quality Indicator [Line Items]
2021	4,453,036
2020	106,802
2019	13,179
2018	1,429
2017	49
Prior	0
Revolving	0
Revolving to Term	0
Total Loans	4,574,495
Pass | Premium finance receivables - life
Financing Receivable, Credit Quality Indicator [Line Items]
2021	340,318
2020	782,936
2019	734,280
2018	673,416
2017	699,250
Prior	3,424,672
Revolving	0
Revolving to Term	0
Total Loans	6,654,872
Pass | Consumer and other
Financing Receivable, Credit Quality Indicator [Line Items]
2021	2,769
2020	1,120
2019	1,254
2018	1,230
2017	84
Prior	4,595
Revolving	10,647
Revolving to Term	0
Total Loans	21,699
Special mention
Financing Receivable, Credit Quality Indicator [Line Items]
2021	54,822
2020	74,796
2019	131,360
2018	123,670
2017	101,923
Prior	189,769
Revolving	111,815
Revolving to Term	6,083
Total Loans	794,238
Special mention | Commercial, industrial and other
Financing Receivable, Credit Quality Indicator [Line Items]
2021	18,468
2020	52,692
2019	67,528
2018	42,470
2017	31,785
Prior	22,358
Revolving	106,454
Revolving to Term	5,841
Total Loans	347,596
Special mention | Commercial PPP loans
Financing Receivable, Credit Quality Indicator [Line Items]
2021	0
2020	1,356
2019	0
2018	0
2017	0
Prior	0
Revolving	0
Revolving to Term	0
Total Loans	1,356
Special mention | Construction and development
Financing Receivable, Credit Quality Indicator [Line Items]
2021	282
2020	8,475
2019	12,144
2018	17,685
2017	23,435
Prior	3,234
Revolving	0
Revolving to Term	0
Total Loans	65,255
Special mention | Non-construction
Financing Receivable, Credit Quality Indicator [Line Items]
2021	3,517
2020	10,307
2019	51,203
2018	61,392
2017	44,193
Prior	155,150
Revolving	0
Revolving to Term	0
Total Loans	325,762
Special mention | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
2021	0
2020	0
2019	0
2018	0
2017	0
Prior	614
Revolving	5,355
Revolving to Term	242
Total Loans	6,211
Special mention | Residential real estate
Financing Receivable, Credit Quality Indicator [Line Items]
2021	884
2020	269
2019	459
2018	2,123
2017	1,848
Prior	8,331
Revolving	0
Revolving to Term	0
Total Loans	13,914
Special mention | Premium finance receivables - commercial
Financing Receivable, Credit Quality Indicator [Line Items]
2021	31,671
2020	1,693
2019	9
2018	0
2017	1
Prior	0
Revolving	0
Revolving to Term	0
Total Loans	33,374
Special mention | Premium finance receivables - life
Financing Receivable, Credit Quality Indicator [Line Items]
2021	0
2020	0
2019	0
2018	0
2017	581
Prior	0
Revolving	0
Revolving to Term	0
Total Loans	581
Special mention | Consumer and other
Financing Receivable, Credit Quality Indicator [Line Items]
2021	0
2020	4
2019	17
2018	0
2017	80
Prior	82
Revolving	6
Revolving to Term	0
Total Loans	189
Substandard accrual
Financing Receivable, Credit Quality Indicator [Line Items]
2021	20,087
2020	10,331
2019	56,495
2018	58,285
2017	34,289
Prior	129,811
Revolving	29,748
Revolving to Term	1,470
Total Loans	340,516
Substandard accrual | Commercial, industrial and other
Financing Receivable, Credit Quality Indicator [Line Items]
2021	17,805
2020	5,246
2019	21,901
2018	33,886
2017	8,712
Prior	41,590
Revolving	28,641
Revolving to Term	820
Total Loans	158,601
Substandard accrual | Commercial PPP loans
Financing Receivable, Credit Quality Indicator [Line Items]
2021	0
2020	280
2019	0
2018	0
2017	0
Prior	0
Revolving	0
Revolving to Term	0
Total Loans	280
Substandard accrual | Construction and development
Financing Receivable, Credit Quality Indicator [Line Items]
2021	0
2020	0
2019	316
2018	2,558
2017	2,132
Prior	478
Revolving	155
Revolving to Term	0
Total Loans	5,639
Substandard accrual | Non-construction
Financing Receivable, Credit Quality Indicator [Line Items]
2021	0
2020	1,960
2019	33,544
2018	20,725
2017	21,345
Prior	69,718
Revolving	0
Revolving to Term	0
Total Loans	147,292
Substandard accrual | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
2021	0
2020	0
2019	0
2018	184
2017	67
Prior	9,341
Revolving	949
Revolving to Term	650
Total Loans	11,191
Substandard accrual | Residential real estate
Financing Receivable, Credit Quality Indicator [Line Items]
2021	1,129
2020	2,234
2019	731
2018	887
2017	2,033
Prior	8,434
Revolving	0
Revolving to Term	0
Total Loans	15,448
Substandard accrual | Premium finance receivables - commercial
Financing Receivable, Credit Quality Indicator [Line Items]
2021	1,153
2020	608
2019	2
2018	45
2017	0
Prior	0
Revolving	0
Revolving to Term	0
Total Loans	1,808
Substandard accrual | Premium finance receivables - life
Financing Receivable, Credit Quality Indicator [Line Items]
2021	0
2020	0
2019	0
2018	0
2017	0
Prior	0
Revolving	0
Revolving to Term	0
Total Loans	0
Substandard accrual | Consumer and other
Financing Receivable, Credit Quality Indicator [Line Items]
2021	0
2020	3
2019	1
2018	0
2017	0
Prior	250
Revolving	3
Revolving to Term	0
Total Loans	257
Substandard nonaccrual/doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
2021	9,847
2020	7,402
2019	6,629
2018	5,336
2017	7,246
Prior	46,421
Revolving	1,059
Revolving to Term	0
Total Loans	83,940
Substandard nonaccrual/doubtful | Commercial, industrial and other
Financing Receivable, Credit Quality Indicator [Line Items]
2021	5,227
2020	3,803
2019	5,008
2018	4,206
2017	2,189
Prior	5,503
Revolving	532
Revolving to Term	0
Total Loans	26,468
Substandard nonaccrual/doubtful | Commercial PPP loans
Financing Receivable, Credit Quality Indicator [Line Items]
2021	0
2020	0
2019	0
2018	0
2017	0
Prior	0
Revolving	0
Revolving to Term	0
Total Loans	0
Substandard nonaccrual/doubtful | Construction and development
Financing Receivable, Credit Quality Indicator [Line Items]
2021	0
2020	0
2019	0
2018	0
2017	0
Prior	1,030
Revolving	0
Revolving to Term	0
Total Loans	1,030
Substandard nonaccrual/doubtful | Non-construction
Financing Receivable, Credit Quality Indicator [Line Items]
2021	0
2020	0
2019	0
2018	112
2017	169
Prior	22,395
Revolving	0
Revolving to Term	0
Total Loans	22,676
Substandard nonaccrual/doubtful | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
2021	0
2020	0
2019	0
2018	47
2017	81
Prior	2,794
Revolving	527
Revolving to Term	0
Total Loans	3,449
Substandard nonaccrual/doubtful | Residential real estate
Financing Receivable, Credit Quality Indicator [Line Items]
2021	0
2020	994
2019	1,554
2018	859
2017	4,807
Prior	14,419
Revolving	0
Revolving to Term	0
Total Loans	22,633
Substandard nonaccrual/doubtful | Premium finance receivables - commercial
Financing Receivable, Credit Quality Indicator [Line Items]
2021	4,620
2020	2,601
2019	67
2018	12
2017	0
Prior	0
Revolving	0
Revolving to Term	0
Total Loans	7,300
Substandard nonaccrual/doubtful | Premium finance receivables - life
Financing Receivable, Credit Quality Indicator [Line Items]
2021	0
2020	0
2019	0
2018	0
2017	0
Prior	0
Revolving	0
Revolving to Term	0
Total Loans	0
Substandard nonaccrual/doubtful | Consumer and other
Financing Receivable, Credit Quality Indicator [Line Items]
2021	0
2020	4
2019	0
2018	100
2017	0
Prior	280
Revolving	0
Revolving to Term	0
Total Loans	$ 384