Consolidated Statements of Changes in Stockholders' Equity - USD ($)	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	AOCI Attributable to Parent [Member]	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 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 stock options exercised and restricted stock vested	(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					17,950,982
Other comprehensive loss, net of tax					1,112,478
Balance at Jun. 30, 2017	13,175,234	158,001,006	135,254,306	(1,347,111)	305,083,435
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 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 stock options exercised and restricted stock vested	(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
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 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 stock options exercised and restricted stock vested	(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					20,995,346
Other comprehensive loss, net of tax					(4,536,161)
Balance at Jun. 30, 2018	13,973,940	190,533,240	171,955,296	(6,874,311)	369,588,165
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 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 stock options exercised and restricted stock vested	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