Revenue from Contracts with Customers (Details) - USD ($) $ in Thousands		3 Months Ended			6 Months Ended
	Jun. 30, 2020	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Disaggregation of Revenue [Line Items]
Noninterest income (in-scope of Topic 606)		$ 53,522		$ 66,933	$ 105,284	$ 138,282
Noninterest income (out-of-scope of Topic 606)(b)		19,921		187,557	63,502	214,515
Total noninterest income		73,443		254,490	168,786	352,796
Whitnell
Disaggregation of Revenue [Line Items]
Gain (Loss) on Sale and Maturity of Other Investments, Before Tax			$ 2,000		2,000
ABRC
Disaggregation of Revenue [Line Items]
Pre-tax book gain on sale	$ 163,000
Wealth management fees
Disaggregation of Revenue [Line Items]
Noninterest income (in-scope of Topic 606)		22,706		20,916	45,120	41,732
Service charges and deposit account fees
Disaggregation of Revenue [Line Items]
Noninterest income (in-scope of Topic 606)		15,549		11,484	30,404	26,706
Card-based fees(a)
Disaggregation of Revenue [Line Items]
Noninterest income (in-scope of Topic 606)		11,009		8,922	20,773	18,529
Insurance commissions and fees
Disaggregation of Revenue [Line Items]
Noninterest income (in-scope of Topic 606)		86		22,430	161	45,038
Other revenue
Disaggregation of Revenue [Line Items]
Noninterest income (in-scope of Topic 606)		4,173		3,181	8,826	6,277
Corporate and Commercial Specialty
Disaggregation of Revenue [Line Items]
Noninterest income (in-scope of Topic 606)		28,751		25,114	57,214	50,150
Noninterest income (out-of-scope of Topic 606)(b)		9,837		10,002	24,404	23,698
Corporate and Commercial Specialty | Wealth management fees
Disaggregation of Revenue [Line Items]
Noninterest income (in-scope of Topic 606)		22,706		20,238	45,120	40,345
Corporate and Commercial Specialty | Service charges and deposit account fees
Disaggregation of Revenue [Line Items]
Noninterest income (in-scope of Topic 606)		4,454		4,307	9,359	7,859
Corporate and Commercial Specialty | Card-based fees(a)
Disaggregation of Revenue [Line Items]
Noninterest income (in-scope of Topic 606)		391		228	826	743
Corporate and Commercial Specialty | Insurance commissions and fees
Disaggregation of Revenue [Line Items]
Noninterest income (in-scope of Topic 606)		38		47	61	123
Corporate and Commercial Specialty | Other revenue
Disaggregation of Revenue [Line Items]
Noninterest income (in-scope of Topic 606)		1,162		294	1,848	1,081
Community, Consumer, and Business
Disaggregation of Revenue [Line Items]
Noninterest income (in-scope of Topic 606)		23,793		41,739	46,570	87,974
Noninterest income (out-of-scope of Topic 606)(b)		7,866		12,394	31,218	19,509
Community, Consumer, and Business | Wealth management fees
Disaggregation of Revenue [Line Items]
Noninterest income (in-scope of Topic 606)		0		678	0	1,387
Community, Consumer, and Business | Service charges and deposit account fees
Disaggregation of Revenue [Line Items]
Noninterest income (in-scope of Topic 606)		11,088		7,173	21,023	18,838
Community, Consumer, and Business | Card-based fees(a)
Disaggregation of Revenue [Line Items]
Noninterest income (in-scope of Topic 606)		10,613		8,647	19,937	17,693
Community, Consumer, and Business | Insurance commissions and fees
Disaggregation of Revenue [Line Items]
Noninterest income (in-scope of Topic 606)		46		22,381	96	44,910
Community, Consumer, and Business | Other revenue
Disaggregation of Revenue [Line Items]
Noninterest income (in-scope of Topic 606)		2,047		2,861	5,514	5,147
Risk Management and Shared Services
Disaggregation of Revenue [Line Items]
Noninterest income (in-scope of Topic 606)		978		80	1,500	158
Noninterest income (out-of-scope of Topic 606)(b)		2,217		165,161	7,879	171,307
Risk Management and Shared Services | Service charges and deposit account fees
Disaggregation of Revenue [Line Items]
Noninterest income (in-scope of Topic 606)		7		4	22	10
Risk Management and Shared Services | Card-based fees(a)
Disaggregation of Revenue [Line Items]
Noninterest income (in-scope of Topic 606)		5		47	9	94
Risk Management and Shared Services | Insurance commissions and fees
Disaggregation of Revenue [Line Items]
Noninterest income (in-scope of Topic 606)		2		3	4	6
Risk Management and Shared Services | Other revenue
Disaggregation of Revenue [Line Items]
Noninterest income (in-scope of Topic 606)		963		26	1,464	49
Operating Segments [Member] | Corporate and Commercial Specialty
Disaggregation of Revenue [Line Items]
Total noninterest income		38,588		35,115	81,619	73,848
Operating Segments [Member] | Community, Consumer, and Business
Disaggregation of Revenue [Line Items]
Total noninterest income		31,660		54,133	77,788	107,483
Operating Segments [Member] | Risk Management and Shared Services
Disaggregation of Revenue [Line Items]
Total noninterest income		$ 3,195		$ 165,242	$ 9,379	$ 171,465