Fair Value of Financial Instruments - Fair Value Estimates (Details) - USD ($) $ in Thousands	Sep. 30, 2022	Dec. 31, 2021
Assets
Investment securities held-to-maturity	$ 1,055,187	$ 384,423
Investment securities available-for-sale	2,661,079	4,273,864
Derivative Assets	83,860	11,989
Accrued interest receivable	66,192	65,728
Liabilities
Derivative Liabilities	12,773	5,263
Level 1
Assets
Cash and cash equivalents	739,211	304,703
Investment securities held-to-maturity	0	0
Investment securities available-for-sale	0	0
Equity securities with readily determinable fair values	1,035
Loans held for sale	0	0
Loans held for investment, net	0	0
Derivative Assets	15	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	7	0
Accrued interest payable	0	2,366
Level 1 | Interest-bearing time deposits with financial institutions
Assets
Cash and cash equivalents	1,733	2,216
Level 2
Assets
Cash and cash equivalents	0	0
Investment securities held-to-maturity	1,055,187	384,423
Investment securities available-for-sale	2,661,079	4,273,864
Equity securities with readily determinable fair values	0
Loans held for sale	2,261	11,959
Loans held for investment, net	0	0
Derivative Assets	8,033	10,100
Accrued interest receivable	66,192	0
Liabilities
Deposit accounts	17,724,242	1,058,822
FHLB advances	582,313	550,093
Other borrowings		8,000
Subordinated debentures	330,742	350,359
Derivative Liabilities	12,766	5,263
Accrued interest payable	8,785	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
Equity securities with readily determinable fair values	0
Loans held for sale	0	0
Loans held for investment, net	14,207,668	14,392,684
Derivative Assets	1,911	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	739,211	304,703
Investment securities held-to-maturity	1,385,502	381,674
Investment securities available-for-sale	2,661,079	4,273,864
Equity securities with readily determinable fair values	1,035
Loans held for sale	2,163	10,869
Loans held for investment, net	14,908,811	14,295,897
Derivative Assets	9,959	11,989
Accrued interest receivable	66,192	65,728
Liabilities
Deposit accounts	17,746,374	17,115,589
FHLB advances	600,000	550,000
Other borrowings		8,000
Subordinated debentures	331,045	330,567
Derivative Liabilities	12,773	5,263
Accrued interest payable	8,785	2,366
Carrying Amount | Interest-bearing time deposits with financial institutions
Assets
Cash and cash equivalents	1,733	2,216
Estimated Fair Value
Assets
Cash and cash equivalents	739,211	304,703
Investment securities held-to-maturity	1,055,187	384,423
Investment securities available-for-sale	2,661,079	4,273,864
Equity securities with readily determinable fair values	1,035
Loans held for sale	2,261	11,959
Loans held for investment, net	14,207,668	14,392,684
Derivative Assets	9,959	11,989
Accrued interest receivable	66,192	65,728
Liabilities
Deposit accounts	17,724,242	17,116,138
FHLB advances	582,313	550,093
Other borrowings		8,000
Subordinated debentures	330,742	350,359
Derivative Liabilities	12,773	5,263
Accrued interest payable	8,785	2,366
Estimated Fair Value | Interest-bearing time deposits with financial institutions
Assets
Cash and cash equivalents	$ 1,733	$ 2,216