Loans and Allowance for Credit Losses for Loans - Internal Loan Classification Risk by Loan Portfolio Class by Origination Year (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Financing Receivable, Credit Quality Indicator [Line Items]
Total	$ 32,314,611	$ 29,699,208
Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
2020	2,686,555
2019	715,352
2018	646,757
2017	336,660
2016	183,908
Prior to 2016	549,676
Revolving Loans Amortized Cost Basis	1,765,170
Revolving Loans Converted to Term Loans	611
Total	6,884,689	4,825,997
Commercial and industrial | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
2020	2,680,515
2019	697,134
2018	644,080
2017	306,259
2016	169,439
Prior to 2016	422,608
Revolving Loans Amortized Cost Basis	1,705,273
Revolving Loans Converted to Term Loans	466
Total	6,625,774
Commercial and industrial | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
2020	77
2019	9,522
2018	1,408
2017	10,669
2016	11,138
Prior to 2016	15,595
Revolving Loans Amortized Cost Basis	45,635
Revolving Loans Converted to Term Loans	88
Total	94,132
Commercial and industrial | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
2020	5,963
2019	7,356
2018	1,269
2017	2,155
2016	3,331
Prior to 2016	13,704
Revolving Loans Amortized Cost Basis	13,040
Revolving Loans Converted to Term Loans	57
Total	46,875
Commercial and industrial | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	1,340
2018	0
2017	17,577
2016	0
Prior to 2016	97,769
Revolving Loans Amortized Cost Basis	1,222
Revolving Loans Converted to Term Loans	0
Total	117,908
Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total	18,293,229	$ 17,643,759
Commercial real estate | Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
2020	1,594,190
2019	3,194,379
2018	2,522,969
2017	2,096,758
2016	1,996,173
Prior to 2016	4,953,045
Revolving Loans Amortized Cost Basis	202,332
Revolving Loans Converted to Term Loans	12,031
Total	16,571,877
Commercial real estate | Commercial real estate | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
2020	1,589,407
2019	3,175,366
2018	2,480,315
2017	2,059,141
2016	1,957,684
Prior to 2016	4,775,400
Revolving Loans Amortized Cost Basis	198,836
Revolving Loans Converted to Term Loans	12,031
Total	16,248,180
Commercial real estate | Commercial real estate | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	18,913
2018	31,799
2017	18,620
2016	32,853
Prior to 2016	73,609
Revolving Loans Amortized Cost Basis	3,496
Revolving Loans Converted to Term Loans	0
Total	179,290
Commercial real estate | Commercial real estate | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
2020	4,783
2019	100
2018	10,855
2017	18,186
2016	5,636
Prior to 2016	102,424
Revolving Loans Amortized Cost Basis	0
Revolving Loans Converted to Term Loans	0
Total	141,984
Commercial real estate | Commercial real estate | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	811
2016	0
Prior to 2016	1,612
Revolving Loans Amortized Cost Basis	0
Revolving Loans Converted to Term Loans	0
Total	2,423
Construction | Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
2020	43,118
2019	135,181
2018	160,452
2017	28,928
2016	61,179
Prior to 2016	100,370
Revolving Loans Amortized Cost Basis	1,192,124
Revolving Loans Converted to Term Loans	0
Total	1,721,352
Construction | Commercial real estate | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
2020	43,118
2019	135,181
2018	160,452
2017	28,928
2016	49,000
Prior to 2016	99,014
Revolving Loans Amortized Cost Basis	1,186,010
Revolving Loans Converted to Term Loans	0
Total	1,701,703
Construction | Commercial real estate | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	9,774
Prior to 2016	435
Revolving Loans Amortized Cost Basis	6,114
Revolving Loans Converted to Term Loans	0
Total	16,323
Construction | Commercial real estate | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	2,405
Prior to 2016	921
Revolving Loans Amortized Cost Basis	0
Revolving Loans Converted to Term Loans	0
Total	$ 3,326