Fair Value of Financial Instruments - Fair Value Estimates (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Assets
Investment securities held-to-maturity	$ 886,050	$ 384,423
Investment securities available-for-sale	3,222,095	4,273,864
Derivative assets	44,880	11,989
Accrued interest receivable	60,922	65,728
Liabilities
Derivative liabilities	4,241	5,263
Level 1
Assets
Cash and cash equivalents	809,259	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	886,050	384,423
Investment securities available-for-sale	3,222,095	4,273,864
Loans held for sale	12,622	11,959
Loans held for investment, net	0	0
Derivative assets	42,972	10,100
Accrued interest receivable	60,922	0
Liabilities
Deposit accounts	17,685,458	1,058,822
FHLB advances	598,334	550,093
Other borrowings		8,000
Subordinated debentures	338,603	350,359
Derivative liabilities	4,241	5,263
Accrued interest payable	5,115	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	14,623,169	14,392,684
Derivative assets	1,908	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	809,259	304,703
Investment securities held-to-maturity	996,382	381,674
Investment securities available-for-sale	3,222,095	4,273,864
Loans held for sale	11,646	10,869
Loans held for investment, net	14,733,755	14,295,897
Derivative assets	44,880	11,989
Accrued interest receivable	60,922	65,728
Liabilities
Deposit accounts	17,689,223	17,115,589
FHLB advances	600,000	550,000
Other borrowings		8,000
Subordinated debentures	330,726	330,567
Derivative liabilities	4,241	5,263
Accrued interest payable	5,115	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	809,259	304,703
Investment securities held-to-maturity	886,050	384,423
Investment securities available-for-sale	3,222,095	4,273,864
Loans held for sale	12,622	11,959
Loans held for investment, net	14,623,169	14,392,684
Derivative assets	44,880	11,989
Accrued interest receivable	60,922	65,728
Liabilities
Deposit accounts	17,685,458	17,116,138
FHLB advances	598,334	550,093
Other borrowings		8,000
Subordinated debentures	338,603	350,359
Derivative liabilities	4,241	5,263
Accrued interest payable	5,115	2,366
Estimated Fair Value | Interest-bearing time deposits with financial institutions
Assets
Cash and cash equivalents	$ 2,216	$ 2,216