Allowance for Credit Losses (Loan Portfolio by Credit Quality Indicator) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Financing Receivable, Credit Quality Indicator [Line Items]
2020	$ 11,439,443
2019	3,923,150
2018	2,926,024
2017	2,548,519
2016	2,074,199
Prior	5,405,389
Revolving	3,731,183
Revolving to Term	31,166
Net loans	32,079,073	$ 26,800,290
Loans with COVID-19 related modifications	235,600
Commercial, industrial and other, excluding PPP loans
Financing Receivable, Credit Quality Indicator [Line Items]
2020	2,106,741
2019	1,368,576
2018	1,005,147
2017	720,535
2016	349,216
Prior	565,324
Revolving	3,106,003
Revolving to Term	18,504
Net loans	9,240,046
Commercial PPP loans
Financing Receivable, Credit Quality Indicator [Line Items]
2020	2,715,921
2019	0
2018	0
2017	0
2016	0
Prior	0
Revolving	0
Revolving to Term	0
Net loans	2,715,921
Construction and development
Financing Receivable, Credit Quality Indicator [Line Items]
2020	305,265
2019	458,936
2018	269,124
2017	167,779
2016	75,630
Prior	66,096
Revolving	28,972
Revolving to Term	0
Net loans	1,371,802
Non-construction
Financing Receivable, Credit Quality Indicator [Line Items]
2020	1,359,557
2019	1,133,136
2018	915,138
2017	861,077
2016	762,114
Prior	1,901,645
Revolving	179,599
Revolving to Term	10,064
Net loans	7,122,330
Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
2020	45
2019	0
2018	366
2017	187
2016	487
Prior	22,549
Revolving	399,031
Revolving to Term	2,598
Net loans	425,263	513,066
Residential real estate
Financing Receivable, Credit Quality Indicator [Line Items]
2020	360,101
2019	320,716
2018	124,304
2017	143,152
2016	122,930
Prior	188,395
Revolving	0
Revolving to Term	0
Net loans	1,259,598	$ 1,354,221
Premium finance receivables - commercial
Financing Receivable, Credit Quality Indicator [Line Items]
2020	4,009,769
2019	40,184
2018	4,487
2017	49
2016	0
Prior	0
Revolving	0
Revolving to Term	0
Net loans	4,054,489
Premium finance receivables - life
Financing Receivable, Credit Quality Indicator [Line Items]
2020	579,716
2019	599,479
2018	605,635
2017	655,101
2016	763,327
Prior	2,654,178
Revolving	0
Revolving to Term	0
Net loans	5,857,436
Consumer and other
Financing Receivable, Credit Quality Indicator [Line Items]
2020	2,328
2019	2,123
2018	1,823
2017	639
2016	495
Prior	7,202
Revolving	17,578
Revolving to Term	0
Net loans	32,188
Pass
Financing Receivable, Credit Quality Indicator [Line Items]
2020	11,330,215
2019	3,629,653
2018	2,660,246
2017	2,323,808
2016	1,871,705
Prior	5,024,558
Revolving	3,536,665
Revolving to Term	24,056
Net loans	30,400,906
Pass | Commercial, industrial and other, excluding PPP loans
Financing Receivable, Credit Quality Indicator [Line Items]
2020	2,050,767
2019	1,199,104
2018	882,508
2017	649,206
2016	282,664
Prior	513,418
Revolving	2,922,136
Revolving to Term	16,515
Net loans	8,516,318
Pass | Commercial PPP loans
Financing Receivable, Credit Quality Indicator [Line Items]
2020	2,715,915
2019	0
2018	0
2017	0
2016	0
Prior	0
Revolving	0
Revolving to Term	0
Net loans	2,715,915
Pass | Construction and development
Financing Receivable, Credit Quality Indicator [Line Items]
2020	301,565
2019	448,704
2018	213,508
2017	135,583
2016	71,883
Prior	58,088
Revolving	28,822
Revolving to Term	0
Net loans	1,258,153
Pass | Non-construction
Financing Receivable, Credit Quality Indicator [Line Items]
2020	1,346,139
2019	1,027,293
2018	833,289
2017	750,825
2016	642,371
Prior	1,623,135
Revolving	179,489
Revolving to Term	7,371
Net loans	6,409,912
Pass | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
2020	45
2019	0
2018	47
2017	28
2016	15
Prior	6,391
Revolving	388,649
Revolving to Term	170
Net loans	395,345
Pass | Residential real estate
Financing Receivable, Credit Quality Indicator [Line Items]
2020	357,381
2019	318,601
2018	119,071
2017	133,055
2016	110,950
Prior	162,876
Revolving	0
Revolving to Term	0
Net loans	1,201,934
Pass | Premium finance receivables - commercial
Financing Receivable, Credit Quality Indicator [Line Items]
2020	3,976,384
2019	34,372
2018	4,368
2017	48
2016	0
Prior	0
Revolving	0
Revolving to Term	0
Net loans	4,015,172
Pass | Premium finance receivables - life
Financing Receivable, Credit Quality Indicator [Line Items]
2020	579,716
2019	599,479
2018	605,635
2017	654,513
2016	763,327
Prior	2,654,178
Revolving	0
Revolving to Term	0
Net loans	5,856,848
Pass | Consumer and other
Financing Receivable, Credit Quality Indicator [Line Items]
2020	2,303
2019	2,100
2018	1,820
2017	550
2016	495
Prior	6,472
Revolving	17,569
Revolving to Term	0
Net loans	31,309
Special mention
Financing Receivable, Credit Quality Indicator [Line Items]
2020	74,044
2019	151,254
2018	165,634
2017	149,652
2016	116,123
Prior	184,038
Revolving	119,580
Revolving to Term	3,747
Net loans	964,072
Special mention | Commercial, industrial and other, excluding PPP loans
Financing Receivable, Credit Quality Indicator [Line Items]
2020	35,305
2019	77,741
2018	44,642
2017	31,131
2016	17,329
Prior	12,695
Revolving	113,137
Revolving to Term	367
Net loans	332,347
Special mention | Commercial PPP loans
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	0
Revolving	0
Revolving to Term	0
Net loans	0
Special mention | Construction and development
Financing Receivable, Credit Quality Indicator [Line Items]
2020	3,700
2019	9,032
2018	48,174
2017	27,439
2016	2,675
Prior	6,338
Revolving	0
Revolving to Term	0
Net loans	97,358
Special mention | Non-construction
Financing Receivable, Credit Quality Indicator [Line Items]
2020	10,885
2019	63,482
2018	70,128
2017	87,985
2016	94,122
Prior	155,080
Revolving	100
Revolving to Term	2,693
Net loans	484,475
Special mention | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	2,302
Revolving	6,337
Revolving to Term	687
Net loans	9,326
Special mention | Residential real estate
Financing Receivable, Credit Quality Indicator [Line Items]
2020	308
2019	644
2018	2,690
2017	2,429
2016	1,997
Prior	7,527
Revolving	0
Revolving to Term	0
Net loans	15,595
Special mention | Premium finance receivables - commercial
Financing Receivable, Credit Quality Indicator [Line Items]
2020	23,830
2019	333
2018	0
2017	0
2016	0
Prior	0
Revolving	0
Revolving to Term	0
Net loans	24,163
Special mention | Premium finance receivables - life
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	588
2016	0
Prior	0
Revolving	0
Revolving to Term	0
Net loans	588
Special mention | Consumer and other
Financing Receivable, Credit Quality Indicator [Line Items]
2020	16
2019	22
2018	0
2017	80
2016	0
Prior	96
Revolving	6
Revolving to Term	0
Net loans	220
Substandard accrual
Financing Receivable, Credit Quality Indicator [Line Items]
2020	26,262
2019	134,374
2018	91,797
2017	62,868
2016	73,340
Prior	139,444
Revolving	69,479
Revolving to Term	2,381
Net loans	599,945
Substandard accrual | Commercial, industrial and other, excluding PPP loans
Financing Receivable, Credit Quality Indicator [Line Items]
2020	19,848
2019	90,112
2018	74,527
2017	37,499
2016	48,356
Prior	30,277
Revolving	68,257
Revolving to Term	762
Net loans	369,638
Substandard accrual | Commercial PPP loans
Financing Receivable, Credit Quality Indicator [Line Items]
2020	6
2019	0
2018	0
2017	0
2016	0
Prior	0
Revolving	0
Revolving to Term	0
Net loans	6
Substandard accrual | Construction and development
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	1,200
2018	5,846
2017	2,897
2016	0
Prior	566
Revolving	150
Revolving to Term	0
Net loans	10,659
Substandard accrual | Non-construction
Financing Receivable, Credit Quality Indicator [Line Items]
2020	2,533
2019	42,091
2018	10,112
2017	20,133
2016	20,381
Prior	92,208
Revolving	10
Revolving to Term	0
Net loans	187,468
Substandard accrual | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	319
2017	0
2016	249
Prior	10,817
Revolving	1,059
Revolving to Term	1,619
Net loans	14,063
Substandard accrual | Residential real estate
Financing Receivable, Credit Quality Indicator [Line Items]
2020	2,412
2019	626
2018	904
2017	2,339
2016	4,354
Prior	5,364
Revolving	0
Revolving to Term	0
Net loans	15,999
Substandard accrual | Premium finance receivables - commercial
Financing Receivable, Credit Quality Indicator [Line Items]
2020	1,455
2019	344
2018	89
2017	0
2016	0
Prior	0
Revolving	0
Revolving to Term	0
Net loans	1,888
Substandard accrual | Premium finance receivables - life
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	0
Revolving	0
Revolving to Term	0
Net loans	0
Substandard accrual | Consumer and other
Financing Receivable, Credit Quality Indicator [Line Items]
2020	8
2019	1
2018	0
2017	0
2016	0
Prior	212
Revolving	3
Revolving to Term	0
Net loans	224
Substandard nonaccrual/doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
2020	8,922
2019	7,869
2018	8,347
2017	12,191
2016	13,031
Prior	57,349
Revolving	5,459
Revolving to Term	982
Net loans	114,150
Substandard nonaccrual/doubtful | Commercial, industrial and other, excluding PPP loans
Financing Receivable, Credit Quality Indicator [Line Items]
2020	821
2019	1,619
2018	3,470
2017	2,699
2016	867
Prior	8,934
Revolving	2,473
Revolving to Term	860
Net loans	21,743
Substandard nonaccrual/doubtful | Commercial PPP loans
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	0
Revolving	0
Revolving to Term	0
Net loans	0
Substandard nonaccrual/doubtful | Construction and development
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	1,596
2017	1,860
2016	1,072
Prior	1,104
Revolving	0
Revolving to Term	0
Net loans	5,632
Substandard nonaccrual/doubtful | Non-construction
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	270
2018	1,609
2017	2,134
2016	5,240
Prior	31,222
Revolving	0
Revolving to Term	0
Net loans	40,475
Substandard nonaccrual/doubtful | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	159
2016	223
Prior	3,039
Revolving	2,986
Revolving to Term	122
Net loans	6,529
Substandard nonaccrual/doubtful | Residential real estate
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	845
2018	1,639
2017	5,329
2016	5,629
Prior	12,628
Revolving	0
Revolving to Term	0
Net loans	26,070
Substandard nonaccrual/doubtful | Premium finance receivables - commercial
Financing Receivable, Credit Quality Indicator [Line Items]
2020	8,100
2019	5,135
2018	30
2017	1
2016	0
Prior	0
Revolving	0
Revolving to Term	0
Net loans	13,266
Substandard nonaccrual/doubtful | Premium finance receivables - life
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	0
Revolving	0
Revolving to Term	0
Net loans	0
Substandard nonaccrual/doubtful | Consumer and other
Financing Receivable, Credit Quality Indicator [Line Items]
2020	1
2019	0
2018	3
2017	9
2016	0
Prior	422
Revolving	0
Revolving to Term	0
Net loans	$ 435