Loans - Balances Of Commercial Loan Portfolio Classes, Disaggregated By PD Grade and Sub Class (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for loan losses	$ 537,881	$ 444,490	$ 200,307	$ 192,749	$ 184,911	$ 180,424
Collectively evaluated for impairment	32,419,020			29,343,285
Allowance - collectively evaluated for impairment	507,677			159,579
Individually evaluated for impairment	289,917			300,726
Allowance - individually evaluated for impairment	30,204			31,181
Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan balance			$ 24,388,108
Loan balances percentage of total			100.00%
Allowance for loan losses			$ 158,598
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	318,722	254,516	122,486	116,096	103,713	98,947
Collectively evaluated for impairment	21,253,367			18,904,621
Allowance - collectively evaluated for impairment	302,145			106,758
Individually evaluated for impairment	140,526			115,808
Allowance - individually evaluated for impairment	16,577			8,484
Commercial | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for loan losses	57,285	$ 47,625	36,112	32,953	$ 34,382	$ 31,311
Collectively evaluated for impairment	4,813,181			3,852,027
Allowance - collectively evaluated for impairment	57,285			32,953
Individually evaluated for impairment	160			1,777
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]
Loan balance			218,287
Allowance for loan losses	18,400		19,100
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	4,768,563		4,242,519
Individually evaluated for impairment	160		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	44,618		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 balance			$ 697,888
Loan balances percentage of total			3.00%
Allowance for loan losses			$ 69
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 balance			$ 815,992
Loan balances percentage of total			4.00%
Allowance for loan losses			$ 165
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 balance			$ 2,098,520
Loan balances percentage of total			9.00%
Allowance for loan losses			$ 274
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 balance			$ 2,657,818
Loan balances percentage of total			11.00%
Allowance for loan losses			$ 738
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 balance			$ 3,725,003
Loan balances percentage of total			15.00%
Allowance for loan losses			$ 8,265
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 balance			$ 4,683,029
Loan balances percentage of total			19.00%
Allowance for loan losses			$ 12,054
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 balance			$ 3,908,971
Loan balances percentage of total			16.00%
Allowance for loan losses			$ 20,409
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 balance			$ 2,166,241
Loan balances percentage of total			9.00%
Allowance for loan losses			$ 22,514
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 balance			$ 1,393,514
Loan balances percentage of total			6.00%
Allowance for loan losses			$ 17,484
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 balance			$ 665,145
Loan balances percentage of total			3.00%
Allowance for loan losses			$ 10,197
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 balance			$ 579,124
Loan balances percentage of total			2.00%
Allowance for loan losses			$ 13,454
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 balance			$ 307,945
Loan balances percentage of total			1.00%
Allowance for loan losses			$ 8,471
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 balance			$ 266,915
Loan balances percentage of total			1.00%
Allowance for loan losses			$ 8,142
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 balance			$ 307,102
Loan balances percentage of total			1.00%
Allowance for loan losses			$ 29,318
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