Fair Value of Financial Instruments - Fair Value Estimates (Details) - USD ($) $ in Thousands	Jun. 30, 2022	Dec. 31, 2021
Assets
Investment securities held-to-maturity	$ 1,156,501	$ 384,423
Investment securities available-for-sale	2,679,070	4,273,864
Derivative Assets	61,161	11,989
Accrued interest receivable	66,898	65,728
Liabilities
Derivative Liabilities	7,984	5,263
Level 1
Assets
Cash and cash equivalents	972,798	304,703
Investment securities held-to-maturity	0	0
Investment securities available-for-sale	0	0
Loans held for sale	0	0
Loans held for investment, net	0	0
Derivative Assets	0	0
Accrued interest receivable	0	65,728
Liabilities
Deposit accounts	0	16,057,316
FHLB advances	0	0
Other borrowings		0
Subordinated debentures	0	0
Derivative Liabilities	0	0
Accrued interest payable	0	2,366
Level 1 | Interest-bearing time deposits with financial institutions
Assets
Cash and cash equivalents	2,216	2,216
Level 2
Assets
Cash and cash equivalents	0	0
Investment securities held-to-maturity	1,156,501	384,423
Investment securities available-for-sale	2,679,070	4,273,864
Loans held for sale	3,100	11,959
Loans held for investment, net	0	0
Derivative Assets	5,606	10,100
Accrued interest receivable	66,898	0
Liabilities
Deposit accounts	18,103,521	1,058,822
FHLB advances	599,403	550,093
Other borrowings		8,000
Subordinated debentures	331,934	350,359
Derivative Liabilities	7,984	5,263
Accrued interest payable	2,866	0
Level 2 | Interest-bearing time deposits with financial institutions
Assets
Cash and cash equivalents	0	0
Level 3
Assets
Cash and cash equivalents	0	0
Investment securities held-to-maturity	0	0
Investment securities available-for-sale	0	0
Loans held for sale	0	0
Loans held for investment, net	14,578,222	14,392,684
Derivative Assets	1,906	1,889
Accrued interest receivable	0	0
Liabilities
Deposit accounts	0	0
FHLB advances	0	0
Other borrowings		0
Subordinated debentures	0	0
Derivative Liabilities	0	0
Accrued interest payable	0	0
Level 3 | Interest-bearing time deposits with financial institutions
Assets
Cash and cash equivalents	0	0
Carrying Amount
Assets
Cash and cash equivalents	972,798	304,703
Investment securities held-to-maturity	1,390,682	381,674
Investment securities available-for-sale	2,679,070	4,273,864
Loans held for sale	2,957	10,869
Loans held for investment, net	15,047,608	14,295,897
Derivative Assets	7,512	11,989
Accrued interest receivable	66,898	65,728
Liabilities
Deposit accounts	18,084,613	17,115,589
FHLB advances	600,000	550,000
Other borrowings		8,000
Subordinated debentures	330,886	330,567
Derivative Liabilities	7,984	5,263
Accrued interest payable	2,866	2,366
Carrying Amount | Interest-bearing time deposits with financial institutions
Assets
Cash and cash equivalents	2,216	2,216
Estimated Fair Value
Assets
Cash and cash equivalents	972,798	304,703
Investment securities held-to-maturity	1,156,501	384,423
Investment securities available-for-sale	2,679,070	4,273,864
Loans held for sale	3,100	11,959
Loans held for investment, net	14,578,222	14,392,684
Derivative Assets	7,512	11,989
Accrued interest receivable	66,898	65,728
Liabilities
Deposit accounts	18,103,521	17,116,138
FHLB advances	599,403	550,093
Other borrowings		8,000
Subordinated debentures	331,934	350,359
Derivative Liabilities	7,984	5,263
Accrued interest payable	2,866	2,366
Estimated Fair Value | Interest-bearing time deposits with financial institutions
Assets
Cash and cash equivalents	$ 2,216	$ 2,216