Fair Value - Estimated fair value and related carrying amount, of the Company's financial instruments (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022	Dec. 31, 2022
Financial assets:
Trading securities	$ 16,039		$ 31,263
SBA servicing asset	6,500		6,100
Financial liabilities:
Other borrowings	900,000
Other derivative financial instruments (mortgage banking related)	(227,559)	$ 119,608
Carrying Amount
Financial assets:
Cash and cash equivalents	1,996,662		1,312,563
Trading securities	16,039		31,263
Investment securities	8,014,663		8,189,780
Loans held for sale	27,289		28,968
Loans, net of allowance for credit losses	30,325,497		29,821,418
Accrued interest receivable	138,515		134,594
Mortgage servicing rights	85,406		86,610
SBA servicing asset	6,521		6,068
Interest rate swap - non-designated hedge	157,014		210,216
Other derivative financial instruments (mortgage banking related)	$ 2,273		$ 800
Derivative Asset, Statement of Financial Position [Extensible Enumeration]	Derivative Asset, Noncurrent		Derivative Asset, Noncurrent
Financial liabilities:
Deposits	$ 36,401,592		$ 36,350,623
Federal funds purchased and securities sold under agreements to repurchase	544,108		556,417
Corporate and subordinated debentures	392,182		392,275
Other borrowings	900,000
Accrued interest payable	20,411		6,218
Interest rate swap - non-designated hedge	806,584		1,033,980
Other derivative financial instruments (mortgage banking related)			163
Fair Value
Financial assets:
Cash and cash equivalents	1,996,662		1,312,563
Trading securities	16,039		31,263
Investment securities	7,567,328		7,756,707
Loans held for sale	27,289		28,968
Loans, net of allowance for credit losses	29,646,800		29,329,499
Accrued interest receivable	138,515		134,594
Mortgage servicing rights	85,406		86,610
Interest rate swap - non-designated hedge	157,014		210,216
Other derivative financial instruments (mortgage banking related)	$ 2,273		$ 800
Derivative Asset, Statement of Financial Position [Extensible Enumeration]	Derivative Asset, Noncurrent		Derivative Asset, Noncurrent
Financial liabilities:
Deposits	$ 36,333,275		$ 36,264,401
Federal funds purchased and securities sold under agreements to repurchase	556,417		556,417
Corporate and subordinated debentures	380,925		377,360
Other borrowings	900,000
Accrued interest payable	20,411		6,218
Interest rate swap - non-designated hedge	806,584		1,033,980
Other derivative financial instruments (mortgage banking related)			163
Commitments to extend credit | Fair Value
Financial liabilities:
Commitments to extend credit	(255,022)		(184,801)
Quoted Prices In Active Markets for Identical Assets (Level 1)
Financial assets:
Cash and cash equivalents	1,996,662		1,312,563
Investment securities	179,717		179,717
Significant Other Observable Inputs (Level 2)
Financial assets:
Trading securities	16,039		31,263
Investment securities	7,387,611		7,576,990
Loans held for sale	27,289		28,968
Accrued interest receivable	26,888		28,449
Interest rate swap - non-designated hedge	157,014		210,216
Other derivative financial instruments (mortgage banking related)	$ 2,273		$ 800
Derivative Asset, Statement of Financial Position [Extensible Enumeration]	Derivative Asset, Noncurrent		Derivative Asset, Noncurrent
Financial liabilities:
Deposits	$ 36,333,275		$ 36,264,401
Federal funds purchased and securities sold under agreements to repurchase	556,417		556,417
Corporate and subordinated debentures	380,925		377,360
Other borrowings	900,000
Accrued interest payable	20,411		3,345
Interest rate swap - non-designated hedge	806,584		1,033,980
Other derivative financial instruments (mortgage banking related)			163
Significant Other Observable Inputs (Level 2) | Commitments to extend credit
Financial liabilities:
Commitments to extend credit	(255,022)		(184,801)
Significant Unobservable Inputs (Level 3)
Financial assets:
Loans, net of allowance for credit losses	29,646,800		29,329,499
Accrued interest receivable	111,627		106,145
Mortgage servicing rights	85,406		86,610
SBA servicing asset	$ 6,521		$ 6,068