Fair Value of Financial Instruments - Fair Value Estimates (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Assets:
Investments held-to-maturity	$ 31,127	$ 18,082
Investment securities available-for-sale, at fair value	874,700	787,429
Accrued interest receivable	27,420	27,060
Level 1
Assets:
Cash and cash equivalents	131,468	197,164
Investments held-to-maturity	0	0
Investment securities available-for-sale, at fair value	0	0
Loans held for sale	0	0
Loans held for investment, net	0	0
Derivative asset	0	0
Accrued interest receivable	27,420	27,060
Liabilities:
Deposit accounts	5,139,299	5,001,053
FHLB advances	0	0
Other borrowings	0	0
Subordinated debentures	0	0
Derivative liability	0	0
Accrued interest payable	1,151	2,131
Level 1 | Interest-bearing time deposits with financial institutions
Assets:
Cash and cash equivalents	6,633	6,633
Level 2
Assets:
Cash and cash equivalents	0	0
Investments held-to-maturity	31,126	18,082
Investment securities available-for-sale, at fair value	874,700	787,429
Loans held for sale	14,940	23,524
Loans held for investment, net	0	0
Derivative asset	3,272	1,135
Accrued interest receivable	0	0
Liabilities:
Deposit accounts	1,160,215	1,074,564
FHLB advances	336,504	489,823
Other borrowings	41,514	46,373
Subordinated debentures	116,004	115,159
Derivative liability	3,272	1,135
Accrued interest payable	0	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
Investments held-to-maturity	0	0
Investment securities available-for-sale, at fair value	0	0
Loans held for sale	0	0
Loans held for investment, net	6,279,915	6,269,366
Derivative asset	0	0
Accrued interest receivable	0	0
Liabilities:
Deposit accounts	0	0
FHLB advances	0	0
Other borrowings	0	0
Subordinated debentures	0	0
Derivative liability	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	131,468	197,164
Investments held-to-maturity	31,965	18,291
Investment securities available-for-sale, at fair value	874,700	787,429
FHLB, FRB and other stock	82,666	65,881
Loans held for sale	13,879	23,426
Loans held for investment, net	6,277,586	6,167,288
Derivative asset	3,272	1,135
Accrued interest receivable	27,420	27,060
Liabilities:
Deposit accounts	6,308,350	6,085,886
FHLB advances	337,638	490,148
Other borrowings	41,462	46,139
Subordinated debentures	105,253	105,123
Derivative liability	3,272	1,135
Accrued interest payable	1,151	2,131
Carrying Amount | Interest-bearing time deposits with financial institutions
Assets:
Cash and cash equivalents	6,633	6,633
Estimated Fair Value
Assets:
Cash and cash equivalents	131,468	197,164
Investments held-to-maturity	31,126	18,082
Investment securities available-for-sale, at fair value	874,700	787,429
Loans held for sale	14,940	23,524
Loans held for investment, net	6,279,915	6,269,366
Derivative asset	3,272	1,135
Accrued interest receivable	27,420	27,060
Liabilities:
Deposit accounts	6,299,514	6,075,617
FHLB advances	336,504	489,823
Other borrowings	41,514	46,373
Subordinated debentures	116,004	115,159
Derivative liability	3,272	1,135
Accrued interest payable	1,151	2,131
Estimated Fair Value | Interest-bearing time deposits with financial institutions
Assets:
Cash and cash equivalents	$ 6,633	$ 6,633