Disclosures About Fair Value of Financial Instruments - Balance Sheet Grouping (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016	Mar. 31, 2016
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale securities	$ 555,632	$ 274,619
Held-to-maturity securities	33,246	34,844
Loans held for sale	17,350	23,989
Loans held for investment	3,012,275	3,098,220	$ 3,168,183
Real estate acquired by foreclosure	1,356	5,220
Level 1
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Cash and short term investments	255,581	389,007
Available-for-sale securities	145,422	112,881
Other securities	18,391	17,983
Loans held for sale	17,350	24,144
Total	436,744	544,015
Level 2
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale securities	410,210	161,738
Held-to-maturity securities	33,246	34,845
Total	443,456	196,583
Financial Liabilities:
Deposits	3,416,066	3,375,047
Securities sold under agreements to repurchase	4,316	3,493
Other borrowed funds	149,440	148,921
Subordinated debentures	47,304	47,492
Total	3,617,126	3,574,953
Level 3
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Loans held for investment	3,036,835	3,128,966
Real estate acquired by foreclosure	1,356	5,220
Total	3,038,191	3,134,186
Carrying Value
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Cash and short term investments	255,581	389,007
Available-for-sale securities	555,632	274,619
Held-to-maturity securities	33,836	35,505
Other securities	18,391	17,983
Loans held for sale	17,350	23,989
Loans held for investment	3,012,275	3,098,220
Real estate acquired by foreclosure	1,356	5,220
Total	3,894,421	3,844,543
Financial Liabilities:
Deposits	3,416,138	3,374,700
Securities sold under agreements to repurchase	4,316	3,493
Other borrowed funds	150,000	150,000
Subordinated debentures	47,304	47,492
Total	3,617,758	3,575,685
Fair Value
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Cash and short term investments	255,581	389,007
Available-for-sale securities	555,632	274,619
Held-to-maturity securities	33,246	34,845
Other securities	18,391	17,983
Loans held for sale	17,350	24,144
Loans held for investment	3,036,835	3,128,966
Real estate acquired by foreclosure	1,356	5,220
Total	3,918,391	3,874,784
Financial Liabilities:
Deposits	3,416,066	3,375,047
Securities sold under agreements to repurchase	4,316	3,493
Other borrowed funds	149,440	148,921
Subordinated debentures	47,304	47,492
Total	$ 3,617,126	$ 3,574,953