Allowance for Credit Losses (Loan Portfolio by Credit Quality Indicator) (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019
Financing Receivable, Credit Quality Indicator [Line Items]
2020	$ 10,453,592
2019	4,130,864
2018	3,243,475
2017	2,657,716
2016	2,183,855
Prior	5,833,724
Revolving	3,601,178
Revolving to Term	31,151
Total Loans	32,135,555	$ 26,800,290	$ 25,710,171
Loans with COVID-19 related modifications	236,300
Commercial, industrial and other
Financing Receivable, Credit Quality Indicator [Line Items]
2020	1,435,852
2019	1,497,027
2018	1,133,989
2017	807,218
2016	423,882
Prior	620,423
Revolving	2,960,069
Revolving to Term	19,526
Total Loans	8,897,986	8,285,920	8,195,602
Commercial PPP Loans
Financing Receivable, Credit Quality Indicator [Line Items]
2020	3,379,013
2019	0
2018	0
2017	0
2016	0
Prior	0
Revolving	0
Revolving to Term	0
Total Loans	3,379,013	0	0
Construction and development
Financing Receivable, Credit Quality Indicator [Line Items]
2020	176,894
2019	475,283
2018	317,727
2017	177,880
2016	86,234
Prior	76,773
Revolving	22,358
Revolving to Term	0
Total Loans	1,333,149	1,283,449	1,042,211
Non-construction
Financing Receivable, Credit Quality Indicator [Line Items]
2020	943,873
2019	1,133,629
2018	1,068,390
2017	895,769
2016	804,928
Prior	2,051,797
Revolving	181,835
Revolving to Term	9,772
Total Loans	7,089,993	6,736,827	6,406,456
Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
2020	47
2019	56
2018	371
2017	511
2016	595
Prior	25,777
Revolving	417,064
Revolving to Term	1,853
Total Loans	446,274	513,066	512,303
Residential real estate
Financing Receivable, Credit Quality Indicator [Line Items]
2020	172,772
2019	370,827
2018	148,698
2017	158,779
2016	133,927
Prior	399,807
Revolving	0
Revolving to Term	0
Total Loans	1,384,810	1,354,221	1,218,666
Premium finance receivables - commercial
Financing Receivable, Credit Quality Indicator [Line Items]
2020	3,935,154
2019	118,096
2018	6,777
2017	117
2016	0
Prior	0
Revolving	0
Revolving to Term	0
Total Loans	4,060,144	3,442,027	3,449,950
Premium finance receivables - life
Financing Receivable, Credit Quality Indicator [Line Items]
2020	408,171
2019	533,284
2018	565,371
2017	616,635
2016	733,758
Prior	2,631,613
Revolving	0
Revolving to Term	0
Total Loans	5,488,832	5,074,602	4,795,496
Consumer and other
Financing Receivable, Credit Quality Indicator [Line Items]
2020	1,816
2019	2,662
2018	2,152
2017	807
2016	531
Prior	27,534
Revolving	19,852
Revolving to Term	0
Total Loans	55,354	$ 110,178	$ 89,487
Pass
Financing Receivable, Credit Quality Indicator [Line Items]
2020	10,356,305
2019	3,732,454
2018	2,908,924
2017	2,410,495
2016	1,974,078
Prior	5,392,161
Revolving	3,384,858
Revolving to Term	25,148
Total Loans	30,184,423
Pass | Commercial, industrial and other
Financing Receivable, Credit Quality Indicator [Line Items]
2020	1,380,874
2019	1,246,209
2018	978,844
2017	688,865
2016	349,659
Prior	554,865
Revolving	2,755,857
Revolving to Term	17,970
Total Loans	7,973,143
Pass | Commercial PPP Loans
Financing Receivable, Credit Quality Indicator [Line Items]
2020	3,379,013
2019	0
2018	0
2017	0
2016	0
Prior	0
Revolving	0
Revolving to Term	0
Total Loans	3,379,013
Pass | Construction and development
Financing Receivable, Credit Quality Indicator [Line Items]
2020	176,894
2019	454,031
2018	255,974
2017	157,559
2016	82,421
Prior	63,379
Revolving	22,358
Revolving to Term	0
Total Loans	1,212,616
Pass | Non-construction
Financing Receivable, Credit Quality Indicator [Line Items]
2020	940,359
2019	1,024,971
2018	957,701
2017	797,355
2016	684,954
Prior	1,736,025
Revolving	180,231
Revolving to Term	7,007
Total Loans	6,328,603
Pass | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
2020	47
2019	0
2018	47
2017	28
2016	37
Prior	6,012
Revolving	406,565
Revolving to Term	171
Total Loans	412,907
Pass | Residential real estate
Financing Receivable, Credit Quality Indicator [Line Items]
2020	171,033
2019	367,779
2018	142,761
2017	149,854
2016	122,718
Prior	373,499
Revolving	0
Revolving to Term	0
Total Loans	1,327,644
Pass | Premium finance receivables - commercial
Financing Receivable, Credit Quality Indicator [Line Items]
2020	3,898,133
2019	103,562
2018	6,077
2017	116
2016	0
Prior	0
Revolving	0
Revolving to Term	0
Total Loans	4,007,888
Pass | Premium finance receivables - life
Financing Receivable, Credit Quality Indicator [Line Items]
2020	408,171
2019	533,284
2018	565,371
2017	616,055
2016	733,758
Prior	2,631,613
Revolving	0
Revolving to Term	0
Total Loans	5,488,252
Pass | Consumer and other
Financing Receivable, Credit Quality Indicator [Line Items]
2020	1,781
2019	2,618
2018	2,149
2017	663
2016	531
Prior	26,768
Revolving	19,847
Revolving to Term	0
Total Loans	54,357
Special mention
Financing Receivable, Credit Quality Indicator [Line Items]
2020	66,682
2019	227,162
2018	205,189
2017	156,740
2016	150,114
Prior	205,640
Revolving	137,321
Revolving to Term	3,468
Total Loans	1,152,316
Special mention | Commercial, industrial and other
Financing Receivable, Credit Quality Indicator [Line Items]
2020	38,670
2019	115,731
2018	75,859
2017	69,144
2016	53,537
Prior	21,993
Revolving	128,730
Revolving to Term	138
Total Loans	503,802
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
Total Loans	0
Special mention | Construction and development
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	20,058
2018	48,593
2017	13,842
2016	2,741
Prior	6,862
Revolving	0
Revolving to Term	0
Total Loans	92,096
Special mention | Non-construction
Financing Receivable, Credit Quality Indicator [Line Items]
2020	2,379
2019	88,103
2018	78,047
2017	69,884
2016	91,313
Prior	164,465
Revolving	737
Revolving to Term	2,765
Total Loans	497,693
Special mention | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	393
2016	83
Prior	3,615
Revolving	7,852
Revolving to Term	565
Total Loans	12,508
Special mention | Residential real estate
Financing Receivable, Credit Quality Indicator [Line Items]
2020	314
2019	1,570
2018	2,686
2017	2,770
2016	2,440
Prior	8,558
Revolving	0
Revolving to Term	0
Total Loans	18,338
Special mention | Premium finance receivables - commercial
Financing Receivable, Credit Quality Indicator [Line Items]
2020	25,295
2019	1,674
2018	4
2017	0
2016	0
Prior	0
Revolving	0
Revolving to Term	0
Total Loans	26,973
Special mention | Premium finance receivables - life
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	580
2016	0
Prior	0
Revolving	0
Revolving to Term	0
Total Loans	580
Special mention | Consumer and other
Financing Receivable, Credit Quality Indicator [Line Items]
2020	24
2019	26
2018	0
2017	127
2016	0
Prior	147
Revolving	2
Revolving to Term	0
Total Loans	326
Substandard accrual
Financing Receivable, Credit Quality Indicator [Line Items]
2020	19,915
2019	157,027
2018	112,864
2017	74,093
2016	39,362
Prior	164,250
Revolving	68,425
Revolving to Term	2,129
Total Loans	638,065
Substandard accrual | Commercial, industrial and other
Financing Receivable, Credit Quality Indicator [Line Items]
2020	15,054
2019	134,060
2018	74,803
2017	43,066
2016	13,169
Prior	31,280
Revolving	66,437
Revolving to Term	1,136
Total Loans	379,005
Substandard accrual | 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
Total Loans	0
Substandard accrual | Construction and development
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	1,194
2018	9,848
2017	3,562
2016	0
Prior	2,853
Revolving	0
Revolving to Term	0
Total Loans	17,457
Substandard accrual | Non-construction
Financing Receivable, Credit Quality Indicator [Line Items]
2020	1,135
2019	19,448
2018	26,611
2017	24,928
2016	20,523
Prior	112,350
Revolving	867
Revolving to Term	0
Total Loans	205,862
Substandard accrual | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	134
2017	0
2016	248
Prior	12,037
Revolving	1,118
Revolving to Term	993
Total Loans	14,530
Substandard accrual | Residential real estate
Financing Receivable, Credit Quality Indicator [Line Items]
2020	1,425
2019	516
2018	1,359
2017	2,537
2016	5,422
Prior	5,500
Revolving	0
Revolving to Term	0
Total Loans	16,759
Substandard accrual | Premium finance receivables - commercial
Financing Receivable, Credit Quality Indicator [Line Items]
2020	2,291
2019	1,803
2018	109
2017	0
2016	0
Prior	0
Revolving	0
Revolving to Term	0
Total Loans	4,203
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
Total Loans	0
Substandard accrual | Consumer and other
Financing Receivable, Credit Quality Indicator [Line Items]
2020	10
2019	6
2018	0
2017	0
2016	0
Prior	230
Revolving	3
Revolving to Term	0
Total Loans	249
Substandard nonaccrual/doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
2020	10,690
2019	14,221
2018	16,498
2017	16,388
2016	20,301
Prior	71,673
Revolving	10,574
Revolving to Term	406
Total Loans	160,751
Substandard nonaccrual/doubtful | Commercial, industrial and other
Financing Receivable, Credit Quality Indicator [Line Items]
2020	1,254
2019	1,027
2018	4,483
2017	6,143
2016	7,517
Prior	12,285
Revolving	9,045
Revolving to Term	282
Total Loans	42,036
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
Total Loans	0
Substandard nonaccrual/doubtful | Construction and development
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	3,312
2017	2,917
2016	1,072
Prior	3,679
Revolving	0
Revolving to Term	0
Total Loans	10,980
Substandard nonaccrual/doubtful | Non-construction
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	1,107
2018	6,031
2017	3,602
2016	8,138
Prior	38,957
Revolving	0
Revolving to Term	0
Total Loans	57,835
Substandard nonaccrual/doubtful | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	56
2018	190
2017	90
2016	227
Prior	4,113
Revolving	1,529
Revolving to Term	124
Total Loans	6,329
Substandard nonaccrual/doubtful | Residential real estate
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	962
2018	1,892
2017	3,618
2016	3,347
Prior	12,250
Revolving	0
Revolving to Term	0
Total Loans	22,069
Substandard nonaccrual/doubtful | Premium finance receivables - commercial
Financing Receivable, Credit Quality Indicator [Line Items]
2020	9,435
2019	11,057
2018	587
2017	1
2016	0
Prior	0
Revolving	0
Revolving to Term	0
Total Loans	21,080
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
Total Loans	0
Substandard nonaccrual/doubtful | Consumer and other
Financing Receivable, Credit Quality Indicator [Line Items]
2020	1
2019	12
2018	3
2017	17
2016	0
Prior	389
Revolving	0
Revolving to Term	0
Total Loans	$ 422