Disclosures About Fair Value of Financial Instruments - Balance Sheet Grouping (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016	Jun. 30, 2016
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale securities	$ 687,100	$ 274,619
Held-to-maturity securities	31,235	34,844
Loans held for sale	18,030	23,989
Loans held for investment	3,123,355	3,098,220	$ 3,189,436
Real estate acquired by foreclosure	921	5,220
Level 1
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Cash and short term investments	134,995	389,007
Available-for-sale securities		112,881
Other securities	25,336	17,983
Loans held for sale		24,144
Total	160,331	544,015
Level 2
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale securities	687,100	161,738
Held-to-maturity securities	31,235	34,845
Total	718,335	196,583
Financial Liabilities:
Deposits	3,360,004	3,375,047
Securities sold under agreements to repurchase	5,221	3,493
Other borrowed funds	304,706	148,921
Subordinated debentures	42,936	47,492
Total	3,712,867	3,574,953
Level 3
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Loans held for sale	18,030
Loans held for investment	3,165,244	3,128,966
Real estate acquired by foreclosure	921	5,220
Total	3,184,195	3,134,186
Carrying Value
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Cash and short term investments	134,995	389,007
Available-for-sale securities	687,100	274,619
Held-to-maturity securities	31,650	35,505
Other securities	25,336	17,983
Loans held for sale	18,030	23,989
Loans held for investment	3,123,355	3,098,220
Real estate acquired by foreclosure	921	5,220
Total	4,021,387	3,844,543
Financial Liabilities:
Deposits	3,360,422	3,374,700
Securities sold under agreements to repurchase	5,221	3,493
Other borrowed funds	305,000	150,000
Subordinated debentures	47,454	47,492
Total	3,718,097	3,575,685
Fair Value
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Cash and short term investments	134,995	389,007
Available-for-sale securities	687,100	274,619
Held-to-maturity securities	31,235	34,845
Other securities	25,336	17,983
Loans held for sale	18,030	24,144
Loans held for investment	3,165,244	3,128,966
Real estate acquired by foreclosure	921	5,220
Total	4,062,861	3,874,784
Financial Liabilities:
Deposits	3,360,004	3,375,047
Securities sold under agreements to repurchase	5,221	3,493
Other borrowed funds	304,706	148,921
Subordinated debentures	42,936	47,492
Total	$ 3,712,867	$ 3,574,953