CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Common Stock [Member] Springfield Bancshares	Common Stock [Member] Bates Companies [Member]	Common Stock [Member] Guaranty Bank and Trust Company [Member]	Common Stock [Member]	Additional Paid-in Capital [Member] Springfield Bancshares	Additional Paid-in Capital [Member] Bates Companies [Member]	Additional Paid-in Capital [Member] Guaranty Bank and Trust Company [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	AOCI Attributable to Parent [Member]	Springfield Bancshares	Bates Companies [Member]	Guaranty Bank and Trust Company [Member]	Total
Balance at Dec. 31, 2016				$ 13,107				$ 156,777	$ 118,617	$ (2,460)				$ 286,041
Net income									35,707					35,707
Other comprehensive income (loss), net of tax										1,092				1,092
Reclassification of certain tax effects from accumulated other comprehensive income									303	(303)
Common cash dividends declared									(2,665)					(2,665)
Issuance of shares of common stock as a result of the acquisition, net of issuance cost			$ 679				$ 30,063						$ 30,742
Issuance of shares of common stock as a result of stock purchased under the Employee Stock Purchase Plan				13				455						468
Issuance of shares of common stock as a result of stock options exercised				114				1,611						1,725
Stock-based compensation expense								1,187						1,187
Restricted stock awards - shares of common stock				28				(28)
Exchange of shares of common stock in connection with payroll taxes for restricted stock and in connection with stock options exercised				(23)				(987)						(1,010)
Balance at Dec. 31, 2017				13,918				189,078	151,962	(1,671)				353,287
Net income									43,120					43,120
Other comprehensive income (loss), net of tax										(3,206)				(3,206)
Impact of adoption of ASU 2016-01									667	(667)
Common cash dividends declared									(3,546)					(3,546)
Issuance of shares of common stock as a result of the acquisition, net of issuance cost	$ 1,699	$ 24			$ 78,832	$ 976					$ 80,531	$ 1,000
Issuance of shares of common stock as a result of stock purchased under the Employee Stock Purchase Plan				15				576						591
Issuance of shares of common stock as a result of stock options exercised				60				734						794
Stock-based compensation expense								1,443						1,443
Restricted stock awards - shares of common stock				23				(23)
Exchange of shares of common stock in connection with payroll taxes for restricted stock and in connection with stock options exercised				(21)				(855)						(876)
Balance at Dec. 31, 2018				15,718				270,761	192,203	(5,544)				473,138
Net income									57,408					57,408
Other comprehensive income (loss), net of tax										4,446				4,446
Common cash dividends declared									(3,775)					(3,775)
Issuance of shares of common stock as a result of the acquisition, net of issuance cost		$ 9				$ 390						$ 399
Issuance of shares of common stock as a result of stock purchased under the Employee Stock Purchase Plan				29				779						808
Issuance of shares of common stock as a result of stock options exercised				59				660						719
Stock-based compensation expense								2,469						2,469
Restricted stock awards - shares of common stock				20				(63)						(43)
Exchange of shares of common stock in connection with payroll taxes for restricted stock and in connection with stock options exercised				(7)				(211)						(218)
Balance at Dec. 31, 2019				$ 15,828				$ 274,785	$ 245,836	$ (1,098)				$ 535,351