CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Common Stock [Member] Springfield Bancshares	Common Stock [Member] Bates Companies	Common Stock [Member]	Additional Paid-in Capital [Member] Springfield Bancshares	Additional Paid-in Capital [Member] Bates Companies	Additional Paid-in Capital [Member]	Retained Earnings [Member]	AOCI Attributable to Parent [Member]	Springfield Bancshares	Bates Companies	Total
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)
Common cash dividends declared							(3,546)				(3,546)
Issuance of shares of common stock as a result of the acquisition, net of issuance cost		$ 24			$ 976					$ 1,000
Issuance of shares of common stock as a result of a merger, net of issuance costs	$ 1,699			$ 78,832					$ 80,531
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 issuance costs	$ 106,327
Stock-based compensation expense						1,443					1,443
Restricted stock awards and restricted stock units of common stock , net of restricted stock units withheld for payment for taxes			$ 23			(23)
Restricted stock awards and restricted stock units of common stock , net of restricted stock units withheld for payment for taxes (in shares)			22,660
Exchange of shares of common stock in connection with payroll taxes for restricted stock vested 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
Impact of adoption of ASU 2016-01							667	(667)
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 and restricted stock units of common stock , net of restricted stock units withheld for payment for taxes			$ 20			(63)					(43)
Restricted stock awards and restricted stock units of common stock , net of restricted stock units withheld for payment for taxes (in shares)			19,869
Exchange of shares of common stock in connection with payroll taxes for restricted stock vested 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
Impact of adoption of ASU 2016-01											245,836
Net income							60,582				60,582
Other comprehensive income (loss), net of tax								2,474			2,474
Repurchase and cancellation of shares of common stock as a result of share repurchase program			(101)			(1,843)	(1,835)				(3,779)
Common cash dividends declared							(3,779)				(3,779)
Issuance of shares of common stock as a result of stock purchased under the Employee Stock Purchase Plan			37			878					915
Issuance of shares of common stock as a result of stock options exercised			42			403					445
Stock-based compensation expense						2,150					2,150
Restricted stock awards and restricted stock units of common stock , net of restricted stock units withheld for payment for taxes			$ 9			304					313
Restricted stock awards and restricted stock units of common stock , net of restricted stock units withheld for payment for taxes (in shares)			8,838
Exchange of shares of common stock in connection with payroll taxes for restricted stock vested and in connection with stock options exercised			$ (9)			(870)					(879)
Balance at Dec. 31, 2020			$ 15,806			$ 275,807	$ 300,804	$ 1,376			593,793
Impact of adoption of ASU 2016-01											$ 300,804