Loans and Allowance for Credit Losses for Loans - Internal Loan Classification Risk by Loan Portfolio Class by Origination Year (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Financing Receivable, Credit Quality Indicator [Line Items]
Total	$ 30,428,067	$ 29,699,208
Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
2020	254,881
2019	827,930
2018	682,755
2017	362,205
2016	239,078
Prior to 2016	598,067
Revolving Loans Amortized Cost Basis	2,033,111
Revolving Loans Converted to Term Loans	704
Total	4,998,731	4,825,997
Commercial and industrial | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
2020	251,561
2019	800,674
2018	677,111
2017	331,265
2016	220,022
Prior to 2016	490,587
Revolving Loans Amortized Cost Basis	1,955,270
Revolving Loans Converted to Term Loans	515
Total	4,727,005
Commercial and industrial | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	11,167
2018	1,614
2017	11,201
2016	11,587
Prior to 2016	15,016
Revolving Loans Amortized Cost Basis	59,157
Revolving Loans Converted to Term Loans	102
Total	109,844
Commercial and industrial | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
2020	3,320
2019	10,870
2018	3,325
2017	1,786
2016	4,832
Prior to 2016	6,252
Revolving Loans Amortized Cost Basis	18,684
Revolving Loans Converted to Term Loans	87
Total	49,156
Commercial and industrial | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	5,219
2018	705
2017	17,953
2016	2,637
Prior to 2016	86,212
Revolving Loans Amortized Cost Basis	0
Revolving Loans Converted to Term Loans	0
Total	112,726
Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total	18,117,282	$ 17,643,759
Commercial real estate | Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
2020	1,042,131
2019	3,297,543
2018	2,625,329
2017	2,171,819
2016	2,076,063
Prior to 2016	4,944,461
Revolving Loans Amortized Cost Basis	220,653
Revolving Loans Converted to Term Loans	12,237
Total	16,390,236
Commercial real estate | Commercial real estate | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
2020	1,037,404
2019	3,269,940
2018	2,611,108
2017	2,133,369
2016	2,041,513
Prior to 2016	4,794,614
Revolving Loans Amortized Cost Basis	217,403
Revolving Loans Converted to Term Loans	12,237
Total	16,117,588
Commercial real estate | Commercial real estate | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
2020	872
2019	22,694
2018	1,748
2017	25,324
2016	23,603
Prior to 2016	75,769
Revolving Loans Amortized Cost Basis	3,250
Revolving Loans Converted to Term Loans	0
Total	153,260
Commercial real estate | Commercial real estate | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
2020	3,855
2019	4,909
2018	12,473
2017	12,288
2016	10,947
Prior to 2016	73,855
Revolving Loans Amortized Cost Basis	0
Revolving Loans Converted to Term Loans	0
Total	118,327
Commercial real estate | Commercial real estate | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	838
2016	0
Prior to 2016	223
Revolving Loans Amortized Cost Basis	0
Revolving Loans Converted to Term Loans	0
Total	1,061
Construction | Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
2020	49,866
2019	157,417
2018	179,300
2017	61,179
2016	76,712
Prior to 2016	57,695
Revolving Loans Amortized Cost Basis	1,144,877
Revolving Loans Converted to Term Loans	0
Total	1,727,046
Construction | Commercial real estate | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
2020	49,866
2019	157,375
2018	179,300
2017	52,820
2016	66,550
Prior to 2016	57,236
Revolving Loans Amortized Cost Basis	1,144,877
Revolving Loans Converted to Term Loans	0
Total	1,708,024
Construction | Commercial real estate | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	7,740
Prior to 2016	96
Revolving Loans Amortized Cost Basis	0
Revolving Loans Converted to Term Loans	0
Total	7,836
Construction | Commercial real estate | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	42
2018	0
2017	8,359
2016	2,422
Prior to 2016	363
Revolving Loans Amortized Cost Basis	0
Revolving Loans Converted to Term Loans	0
Total	$ 11,186