Fair Value - Estimated fair value and related carrying amount, of the Company's financial instruments (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022
Financial assets:
Trading securities	$ 114,154		$ 31,263
SBA servicing asset	5,700		6,100
Financial liabilities:
Other derivative financial instruments (mortgage banking related)	217,735	$ 790,388
Carrying Amount
Financial assets:
Cash and cash equivalents	1,329,137		1,312,563
Trading securities	114,154		31,263
Investment securities	7,344,483		8,189,780
Loans held for sale	27,443		28,968
Loans, net of allowance for credit losses	31,568,716		29,821,418
Accrued interest receivable	151,259		134,594
Mortgage servicing rights	89,476		86,610
SBA servicing asset	5,654		6,068
Interest rate swap - non-designated hedge	211,109		210,216
Other derivative financial instruments (mortgage banking related)	$ 1,236		$ 800
Derivative Asset, Statement of Financial Position [Extensible Enumeration]	Derivative Asset, Noncurrent		Derivative Asset, Noncurrent
Financial liabilities:
Noninterest-bearing	$ 11,158,431		$ 13,168,656
Interest-bearing other than time deposits	21,322,840		20,761,981
Time deposits	4,453,927		2,419,986
Federal funds purchased and securities sold under agreements to repurchase	513,304		556,417
Corporate and subordinated debentures	391,997		392,275
Accrued interest payable	45,163		6,218
Interest rate swap - non-designated hedge	1,251,059		1,033,980
Other derivative financial instruments (mortgage banking related)			163
Other derivative financial instruments (mortgage banking related)	819
Fair Value
Financial assets:
Cash and cash equivalents	1,329,137		1,312,563
Trading securities	114,154		31,263
Investment securities	6,823,170		7,756,707
Loans held for sale	27,443		28,968
Loans, net of allowance for credit losses	29,773,087		29,329,499
Accrued interest receivable	151,259		134,594
Mortgage servicing rights	89,476		86,610
SBA servicing asset	5,654
Interest rate swap - non-designated hedge	211,109		210,216
Other derivative financial instruments (mortgage banking related)	1,236		800
Financial liabilities:
Noninterest-bearing	11,158,431		13,168,656
Interest-bearing other than time deposits	21,322,840		20,761,981
Time deposits	4,391,875		2,333,764
Federal funds purchased and securities sold under agreements to repurchase	513,304		556,417
Corporate and subordinated debentures	376,373		377,360
Accrued interest payable	45,163		6,218
Interest rate swap - non-designated hedge	1,251,059		1,033,980
Other derivative financial instruments (mortgage banking related)			163
Other derivative financial instruments (mortgage banking related)	819
Commitments to extend credit | Fair Value
Financial liabilities:
Commitments to extend credit	(604,493)		(184,801)
Quoted Prices In Active Markets for Identical Assets (Level 1)
Financial assets:
Cash and cash equivalents	1,329,137		1,312,563
Investment securities	187,152		179,717
Significant Other Observable Inputs (Level 2)
Financial assets:
Trading securities	114,154		31,263
Investment securities	6,636,018		7,576,990
Loans held for sale	27,443		28,968
Accrued interest receivable	26,561		28,449
Interest rate swap - non-designated hedge	211,109		210,216
Other derivative financial instruments (mortgage banking related)	1,236		800
Financial liabilities:
Noninterest-bearing	11,158,431		13,168,656
Interest-bearing other than time deposits	21,322,840		20,761,981
Time deposits	4,391,875		2,333,764
Federal funds purchased and securities sold under agreements to repurchase	513,304		556,417
Corporate and subordinated debentures	376,373		377,360
Accrued interest payable	45,163		3,345
Interest rate swap - non-designated hedge	1,251,059		1,033,980
Other derivative financial instruments (mortgage banking related)			163
Other derivative financial instruments (mortgage banking related)	819
Significant Other Observable Inputs (Level 2) | Commitments to extend credit
Financial liabilities:
Commitments to extend credit	(604,493)		(184,801)
Significant Unobservable Inputs (Level 3)
Financial assets:
Loans, net of allowance for credit losses	29,773,087		29,329,499
Accrued interest receivable	124,698		106,145
Mortgage servicing rights	89,476		86,610
SBA servicing asset	$ 5,654		$ 6,068