Consolidated Statements of Changes in Stockholders' Equity - USD ($)	Common Stock [Member] Springfield Bancshares	Common Stock [Member]	Additional Paid-in Capital [Member] Springfield Bancshares	Additional Paid-in Capital [Member]	Retained Earnings [Member]	AOCI Attributable to Parent [Member]	Springfield Bancshares	Total
Balance at Dec. 31, 2016		$ 13,106,845		$ 156,776,642	$ 118,616,901	$ (2,459,589)		$ 286,040,799
Net income					9,184,965			9,184,965
Other comprehensive income (loss), net of tax						410,739		410,739
Common cash dividends declared					(656,574)			(656,574)
Issuance of shares of common stock as a result of stock purchased under the Employee Stock Purchase Plan		3,573		83,091				86,664
Issuance of shares of common stock as a result of stock options exercised		44,284		630,290				674,574
Stock-based compensation expense				388,753				388,753
Restricted stock awards - shares of common stock		13,289		(13,289)
Exchange of shares of common stock in connection with payroll taxes for restricted stock and in connection with stock options exercised		(6,772)		(283,518)				(290,290)
Balance at Mar. 31, 2017		13,161,219		157,581,969	127,145,292	(2,048,850)		295,839,630
Balance at Dec. 31, 2016		13,106,845		156,776,642	118,616,901	(2,459,589)		286,040,799
Net income								25,804,917
Other comprehensive income (loss), net of tax								1,387,055
Balance at Sep. 30, 2017		13,201,959		158,459,072	142,450,131	(1,072,534)		313,038,628
Balance at Mar. 31, 2017		13,161,219		157,581,969	127,145,292	(2,048,850)		295,839,630
Net income					8,766,017			8,766,017
Other comprehensive income (loss), net of tax						701,739		701,739
Common cash dividends declared					(657,003)			(657,003)
Issuance of shares of common stock as a result of stock purchased under the Employee Stock Purchase Plan		4,582		170,061				174,643
Issuance of shares of common stock as a result of stock options exercised		8,027		109,392				117,419
Stock-based compensation expense				168,314				168,314
Restricted stock awards - shares of common stock		2,000		(2,000)
Exchange of shares of common stock in connection with payroll taxes for restricted stock and in connection with stock options exercised		(594)		(26,730)				(27,324)
Balance at Jun. 30, 2017		13,175,234		158,001,006	135,254,306	(1,347,111)		305,083,435
Net income					7,853,935			7,853,935
Other comprehensive income (loss), net of tax						274,577		274,577
Common cash dividends declared					(658,110)			(658,110)
Issuance of shares of common stock as a result of stock purchased under the Employee Stock Purchase Plan		2,319		88,052				90,371
Issuance of shares of common stock as a result of stock options exercised		19,906		73,915				93,821
Stock-based compensation expense				300,599				300,599
Restricted stock awards - shares of common stock		4,500		(4,500)
Balance at Sep. 30, 2017		13,201,959		158,459,072	142,450,131	(1,072,534)		313,038,628
Balance at Dec. 31, 2017		13,918,168		189,077,550	151,962,661	(1,671,250)		353,287,129
Net income					10,549,961			10,549,961
Other comprehensive income (loss), net of tax						(3,201,540)		(3,201,540)
Impact of adoption of ASU 2016-01 | ASU 2016-01					666,900	(666,900)
Common cash dividends declared					(833,730)			(833,730)
Issuance of shares of common stock as a result of stock purchased under the Employee Stock Purchase Plan		2,669		100,262				102,931
Issuance of shares of common stock as a result of stock options exercised		13,074		192,522				205,596
Stock-based compensation expense				495,493				495,493
Restricted stock awards - shares of common stock		6,860		(6,860)
Exchange of shares of common stock in connection with payroll taxes for restricted stock and in connection with stock options exercised		(3,814)		(174,109)				(177,923)
Balance at Mar. 31, 2018		13,936,957		189,684,858	162,345,792	(5,539,690)		360,427,917
Balance at Dec. 31, 2017		13,918,168		189,077,550	151,962,661	(1,671,250)		353,287,129
Net income								29,804,181
Other comprehensive income (loss), net of tax								(5,148,048)
Balance at Sep. 30, 2018		15,673,760		269,373,303	179,826,524	(7,486,198)		457,387,389
Balance at Mar. 31, 2018		13,936,957		189,684,858	162,345,792	(5,539,690)		360,427,917
Net income					10,445,385			10,445,385
Other comprehensive income (loss), net of tax						(1,334,621)		(1,334,621)
Common cash dividends declared					(835,881)			(835,881)
Issuance of shares of common stock as a result of stock purchased under the Employee Stock Purchase Plan		5,728		215,173				220,901
Issuance of shares of common stock as a result of stock options exercised		26,641		362,292				388,933
Stock-based compensation expense				291,912				291,912
Restricted stock awards - shares of common stock		3,972		(3,972)
Exchange of shares of common stock in connection with payroll taxes for restricted stock and in connection with stock options exercised		642		(17,023)				(16,381)
Balance at Jun. 30, 2018		13,973,940		190,533,240	171,955,296	(6,874,311)		369,588,165
Net income					8,808,835			8,808,835
Other comprehensive income (loss), net of tax						(611,887)		(611,887)
Common cash dividends declared					(937,607)			(937,607)
Issuance of shares of common stock, net of issuance costs	$ 1,699,414		$ 78,831,543				$ 80,530,957
Issuance of shares of common stock as a result of stock purchased under the Employee Stock Purchase Plan		3,205		120,396				123,601
Issuance of shares of common stock as a result of stock options exercised		1,754		32,300				34,054
Stock-based compensation expense				318,906				318,906
Restricted stock awards - shares of common stock		5,300		(5,300)
Exchange of shares of common stock in connection with payroll taxes for restricted stock and in connection with stock options exercised		(9,853)		(457,782)				(467,635)
Balance at Sep. 30, 2018		$ 15,673,760		$ 269,373,303	$ 179,826,524	$ (7,486,198)		$ 457,387,389