Loans - Balances Of Commercial Loan Portfolio Classes, Disaggregated By PD Grade and Sub Class (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for loan losses	$ 444,490	$ 200,307	$ 184,911	$ 180,424
Collectively evaluated for impairment	33,124,956		27,638,617
Allowance - collectively evaluated for impairment	419,227		153,692
Individually evaluated for impairment	253,347		275,148
Allowance - individually evaluated for impairment	25,263		27,806
Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan Balances As A Percentage Of Commercial Loans		100.00%
Allowance for loan losses		$ 158,598
Loan balance		24,388,108
Collectively evaluated for impairment		$ 24,273,207
Percent Loan Collectively Evaluated For Impairment		100.00%
Allowance - collectively evaluated for impairment		$ 151,554
Individually evaluated for impairment		$ 84,001
Percent Loan Individually Evaluated For Impairment		0.00%
Allowance - individually evaluated for impairment		$ 6,196
Purchased credit-impaired loans		$ 30,900
Percent Loan Purchased Credit Impaired		0.00%
Allowance - purchased credit-impaired loans		$ 848
Commercial | Commercial, financial, and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for loan losses	254,516	122,486	103,713	98,947
Collectively evaluated for impairment	22,024,338		17,056,034
Allowance - collectively evaluated for impairment	243,115		98,135
Individually evaluated for impairment	100,092		83,253
Allowance - individually evaluated for impairment	11,401		3,437
Commercial | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for loan losses	47,625	36,112	34,382	$ 31,311
Collectively evaluated for impairment	4,639,529		3,936,727
Allowance - collectively evaluated for impairment	47,625		34,382
Individually evaluated for impairment	163		1,879
Allowance - individually evaluated for impairment	0		$ 0
C&I | Commercial | Commercial, financial, and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan balance		15,421,921
Collectively evaluated for impairment		15,313,558
Individually evaluated for impairment		82,438
Purchased credit-impaired loans		25,925
Loans to Mortgage Companies | Commercial | Commercial, financial, and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan balance		4,410,883
Collectively evaluated for impairment		4,410,883
Individually evaluated for impairment		0
Purchased credit-impaired loans		0
TRUPS | Commercial | Commercial, financial, and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for loan losses	18,900	19,100
Loan balance		218,287
Collectively evaluated for impairment		218,287
Individually evaluated for impairment		0
Purchased credit-impaired loans		0
Income CRE | Commercial | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan balance		4,248,237
Collectively evaluated for impairment	4,565,240	4,242,519
Individually evaluated for impairment	163	1,563
Purchased credit-impaired loans		4,155
Residential CRE | Commercial | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan balance		88,780
Collectively evaluated for impairment	74,289	87,960
Individually evaluated for impairment	$ 0	0
Purchased credit-impaired loans		$ 820
PD Grade 1 | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan Balances As A Percentage Of Commercial Loans		3.00%
Allowance for loan losses		$ 69
Loan balance		697,888
PD Grade 1 | C&I | Commercial | Commercial, financial, and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan balance		696,040
PD Grade 1 | Loans to Mortgage Companies | Commercial | Commercial, financial, and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan balance		0
PD Grade 1 | TRUPS | Commercial | Commercial, financial, and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan balance		0
PD Grade 1 | Income CRE | Commercial | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan balance		1,848
PD Grade 1 | Residential CRE | Commercial | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan balance		$ 0
PD Grade 2 | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan Balances As A Percentage Of Commercial Loans		4.00%
Allowance for loan losses		$ 165
Loan balance		815,992
PD Grade 2 | C&I | Commercial | Commercial, financial, and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan balance		767,048
PD Grade 2 | Loans to Mortgage Companies | Commercial | Commercial, financial, and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan balance		0
PD Grade 2 | TRUPS | Commercial | Commercial, financial, and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan balance		0
PD Grade 2 | Income CRE | Commercial | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan balance		48,906
PD Grade 2 | Residential CRE | Commercial | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan balance		$ 38
PD Grade 3 | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan Balances As A Percentage Of Commercial Loans		9.00%
Allowance for loan losses		$ 274
Loan balance		2,098,520
PD Grade 3 | C&I | Commercial | Commercial, financial, and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan balance		743,123
PD Grade 3 | Loans to Mortgage Companies | Commercial | Commercial, financial, and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan balance		877,210
PD Grade 3 | TRUPS | Commercial | Commercial, financial, and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan balance		3,314
PD Grade 3 | Income CRE | Commercial | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan balance		474,067
PD Grade 3 | Residential CRE | Commercial | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan balance		$ 806
PD Grade 4 | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan Balances As A Percentage Of Commercial Loans		11.00%
Allowance for loan losses		$ 738
Loan balance		2,657,818
PD Grade 4 | C&I | Commercial | Commercial, financial, and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan balance		1,237,772
PD Grade 4 | Loans to Mortgage Companies | Commercial | Commercial, financial, and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan balance		692,971
PD Grade 4 | TRUPS | Commercial | Commercial, financial, and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan balance		46,375
PD Grade 4 | Income CRE | Commercial | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan balance		680,223
PD Grade 4 | Residential CRE | Commercial | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan balance		$ 477
PD Grade 5 | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan Balances As A Percentage Of Commercial Loans		15.00%
Allowance for loan losses		$ 8,265
Loan balance		3,725,003
PD Grade 5 | C&I | Commercial | Commercial, financial, and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan balance		1,986,761
PD Grade 5 | Loans to Mortgage Companies | Commercial | Commercial, financial, and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan balance		670,402
PD Grade 5 | TRUPS | Commercial | Commercial, financial, and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan balance		72,512
PD Grade 5 | Income CRE | Commercial | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan balance		993,628
PD Grade 5 | Residential CRE | Commercial | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan balance		$ 1,700
PD Grade 6 | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan Balances As A Percentage Of Commercial Loans		19.00%
Allowance for loan losses		$ 12,054
Loan balance		4,683,029
PD Grade 6 | C&I | Commercial | Commercial, financial, and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan balance		2,511,290
PD Grade 6 | Loans to Mortgage Companies | Commercial | Commercial, financial, and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan balance		1,410,387
PD Grade 6 | TRUPS | Commercial | Commercial, financial, and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan balance		27,263
PD Grade 6 | Income CRE | Commercial | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan balance		717,062
PD Grade 6 | Residential CRE | Commercial | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan balance		$ 17,027
PD Grade 7 | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan Balances As A Percentage Of Commercial Loans		16.00%
Allowance for loan losses		$ 20,409
Loan balance		3,908,971
PD Grade 7 | C&I | Commercial | Commercial, financial, and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan balance		2,708,707
PD Grade 7 | Loans to Mortgage Companies | Commercial | Commercial, financial, and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan balance		509,616
PD Grade 7 | TRUPS | Commercial | Commercial, financial, and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan balance		18,378
PD Grade 7 | Income CRE | Commercial | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan balance		641,345
PD Grade 7 | Residential CRE | Commercial | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan balance		$ 30,925
PD Grade 8 | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan Balances As A Percentage Of Commercial Loans		9.00%
Allowance for loan losses		$ 22,514
Loan balance		2,166,241
PD Grade 8 | C&I | Commercial | Commercial, financial, and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan balance		1,743,364
PD Grade 8 | Loans to Mortgage Companies | Commercial | Commercial, financial, and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan balance		136,771
PD Grade 8 | TRUPS | Commercial | Commercial, financial, and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan balance		0
PD Grade 8 | Income CRE | Commercial | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan balance		269,407
PD Grade 8 | Residential CRE | Commercial | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan balance		$ 16,699
PD Grade 9 | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan Balances As A Percentage Of Commercial Loans		6.00%
Allowance for loan losses		$ 17,484
Loan balance		1,393,514
PD Grade 9 | C&I | Commercial | Commercial, financial, and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan balance		1,101,873
PD Grade 9 | Loans to Mortgage Companies | Commercial | Commercial, financial, and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan balance		77,139
PD Grade 9 | TRUPS | Commercial | Commercial, financial, and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan balance		31,909
PD Grade 9 | Income CRE | Commercial | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan balance		169,586
PD Grade 9 | Residential CRE | Commercial | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan balance		$ 13,007
PD Grade 10 | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan Balances As A Percentage Of Commercial Loans		3.00%
Allowance for loan losses		$ 10,197
Loan balance		665,145
PD Grade 10 | C&I | Commercial | Commercial, financial, and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan balance		563,635
PD Grade 10 | Loans to Mortgage Companies | Commercial | Commercial, financial, and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan balance		21,229
PD Grade 10 | TRUPS | Commercial | Commercial, financial, and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan balance		18,536
PD Grade 10 | Income CRE | Commercial | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan balance		59,592
PD Grade 10 | Residential CRE | Commercial | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan balance		$ 2,153
PD Grade 11 | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan Balances As A Percentage Of Commercial Loans		2.00%
Allowance for loan losses		$ 13,454
Loan balance		579,124
PD Grade 11 | C&I | Commercial | Commercial, financial, and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan balance		495,140
PD Grade 11 | Loans to Mortgage Companies | Commercial | Commercial, financial, and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan balance		0
PD Grade 11 | TRUPS | Commercial | Commercial, financial, and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan balance		0
PD Grade 11 | Income CRE | Commercial | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan balance		81,682
PD Grade 11 | Residential CRE | Commercial | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan balance		$ 2,302
PD Grade 12 | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan Balances As A Percentage Of Commercial Loans		1.00%
Allowance for loan losses		$ 8,471
Loan balance		307,945
PD Grade 12 | C&I | Commercial | Commercial, financial, and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan balance		262,906
PD Grade 12 | Loans to Mortgage Companies | Commercial | Commercial, financial, and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan balance		15,158
PD Grade 12 | TRUPS | Commercial | Commercial, financial, and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan balance		0
PD Grade 12 | Income CRE | Commercial | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan balance		28,807
PD Grade 12 | Residential CRE | Commercial | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan balance		$ 1,074
PD Grade 13 | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan Balances As A Percentage Of Commercial Loans		1.00%
Allowance for loan losses		$ 8,142
Loan balance		266,915
PD Grade 13 | C&I | Commercial | Commercial, financial, and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan balance		232,823
PD Grade 13 | Loans to Mortgage Companies | Commercial | Commercial, financial, and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan balance		0
PD Grade 13 | TRUPS | Commercial | Commercial, financial, and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan balance		0
PD Grade 13 | Income CRE | Commercial | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan balance		32,966
PD Grade 13 | Residential CRE | Commercial | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan balance		$ 1,126
PD Grade 14 15 16 | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan Balances As A Percentage Of Commercial Loans		1.00%
Allowance for loan losses		$ 29,318
Loan balance		307,102
PD Grade 14 15 16 | C&I | Commercial | Commercial, financial, and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan balance		263,076
PD Grade 14 15 16 | Loans to Mortgage Companies | Commercial | Commercial, financial, and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan balance		0
PD Grade 14 15 16 | TRUPS | Commercial | Commercial, financial, and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan balance		0
PD Grade 14 15 16 | Income CRE | Commercial | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan balance		43,400
PD Grade 14 15 16 | Residential CRE | Commercial | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan balance		$ 626