Loans and Allowance for Credit Losses for Loans - Internal Loan Classification Risk by Loan Portfolio Class by Origination Year (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Financing Receivable, Credit Quality Indicator [Line Items]
Total	$ 32,415,586	$ 29,699,208
Commercial and Industrial
Financing Receivable, Credit Quality Indicator [Line Items]
2020	2,662,790
2019	628,164
2018	538,406
2017	275,871
2016	203,335
Prior to 2016	918,755
Revolving Loans Amortized Cost Basis	1,675,515
Revolving Loans Converted to Term Loans	509
Total	6,903,345	4,825,997
Commercial and Industrial | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
2020	2,656,655
2019	609,142
2018	523,833
2017	246,684
2016	185,298
Prior to 2016	804,896
Revolving Loans Amortized Cost Basis	1,613,011
Revolving Loans Converted to Term Loans	417
Total	6,639,936
Commercial and Industrial | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
2020	724
2019	10,634
2018	11,786
2017	10,236
2016	11,310
Prior to 2016	14,895
Revolving Loans Amortized Cost Basis	44,412
Revolving Loans Converted to Term Loans	68
Total	104,065
Commercial and Industrial | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
2020	5,411
2019	3,181
2018	2,780
2017	1,789
2016	4,095
Prior to 2016	26,720
Revolving Loans Amortized Cost Basis	18,092
Revolving Loans Converted to Term Loans	24
Total	62,092
Commercial and Industrial | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	5,207
2018	7
2017	17,162
2016	2,632
Prior to 2016	72,244
Revolving Loans Amortized Cost Basis	0
Revolving Loans Converted to Term Loans	0
Total	97,252
Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total	18,536,362	17,643,759
Commercial real estate | Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
2020	2,498,200
2019	3,245,506
2018	2,410,684
2017	2,023,598
2016	1,982,888
Prior to 2016	4,446,596
Revolving Loans Amortized Cost Basis	192,489
Revolving Loans Converted to Term Loans	15,626
Total	16,815,587	15,996,741
Commercial real estate | Commercial real estate | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
2020	2,456,797
2019	3,236,056
2018	2,360,488
2017	1,993,600
2016	1,929,677
Prior to 2016	4,281,267
Revolving Loans Amortized Cost Basis	189,008
Revolving Loans Converted to Term Loans	15,626
Total	16,462,519
Commercial real estate | Commercial real estate | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
2020	23,864
2019	0
2018	26,028
2017	7,197
2016	42,882
Prior to 2016	86,098
Revolving Loans Amortized Cost Basis	3,481
Revolving Loans Converted to Term Loans	0
Total	189,550
Commercial real estate | Commercial real estate | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
2020	17,539
2019	9,450
2018	24,168
2017	22,014
2016	10,329
Prior to 2016	78,322
Revolving Loans Amortized Cost Basis	0
Revolving Loans Converted to Term Loans	0
Total	161,822
Commercial real estate | Commercial real estate | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	787
2016	0
Prior to 2016	909
Revolving Loans Amortized Cost Basis	0
Revolving Loans Converted to Term Loans	0
Total	1,696
Construction | Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
2020	105,422
2019	157,438
2018	123,662
2017	18,824
2016	59,682
Prior to 2016	61,043
Revolving Loans Amortized Cost Basis	1,194,704
Revolving Loans Converted to Term Loans	0
Total	1,720,775	$ 1,647,018
Construction | Commercial real estate | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
2020	105,422
2019	157,407
2018	123,416
2017	16,196
2016	47,202
Prior to 2016	60,663
Revolving Loans Amortized Cost Basis	1,162,297
Revolving Loans Converted to Term Loans	0
Total	1,672,603
Construction | Commercial real estate | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	10,058
Prior to 2016	0
Revolving Loans Amortized Cost Basis	32,407
Revolving Loans Converted to Term Loans	0
Total	42,465
Construction | Commercial real estate | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	31
2018	246
2017	2,628
2016	2,422
Prior to 2016	380
Revolving Loans Amortized Cost Basis	0
Revolving Loans Converted to Term Loans	0
Total	$ 5,707