Statements of changes in Stockholders' Equity (Deficit) - USD ($)	Common Stock Common Class A	Common Stock Common Class C	Additional Paid-in Capital	AOCI Attributable to Parent	Retained Earnings	Treasury Stock	Total
Stockholders' Equity Attributable to Parent, Beginning Balance at Dec. 31, 2017	$ 29,071,154	$ 4,178,748	$ 38,125,042	$ 603,170	$ 77,520,951	$ (931,075)	$ 148,567,990
Cumulative effect adjustment upon adoption of new accounting standard (ASU 2016-01)	0	0	0	(603,170)	603,170	0	0
Net earnings	0	0	0	0	16,925,923	0	16,925,923
Share-based Payment Arrangement, Amount Capitalized	0	0	58,087	0	0	0	58,087
Proceeds from stock options exercised	63,968	0	(22,115)	0	0	0	41,853
Benefit plans funded with treasury stock	0	0	88,964	0	0	222,410	311,374
Stock dividends	3,520	(4)	5,362	0	(8,878)	0	0
Stockholders' Equity Attributable to Parent, Ending Balance at Mar. 31, 2018	29,138,642	4,178,744	38,255,340	0	95,041,166	(708,665)	165,905,227
Stockholders' Equity Attributable to Parent, Beginning Balance at Dec. 31, 2017	29,071,154	4,178,748	38,125,042	603,170	77,520,951	(931,075)	148,567,990
Net earnings							22,177,886
Other comprehensive income, net of income tax							(687)
Share-based Payment Arrangement, Amount Capitalized							174,831
Proceeds from stock options exercised							57,412
Benefit plans funded with treasury stock							1,108,583
Payments to acquire treasury stock							(54,507)
Stockholders' Equity Attributable to Parent, Ending Balance at Sep. 30, 2018	29,147,316	4,178,368	38,711,180	(687)	100,293,129	(297,798)	172,031,508
Stockholders' Equity Attributable to Parent, Beginning Balance at Mar. 31, 2018	29,138,642	4,178,744	38,255,340	0	95,041,166	(708,665)	165,905,227
Net earnings	0	0	0	0	3,238,217	0	3,238,217
Other comprehensive income, net of income tax	0	0	0	(1,448)	0	0	(1,448)
Share-based Payment Arrangement, Amount Capitalized	0	0	58,053	0	0	0	58,053
Benefit plans funded with treasury stock	0	0	163,335	0	0	222,420	385,755
Conversion Class C to Class A	376	(376)	0	0	0	0	0
Stockholders' Equity Attributable to Parent, Ending Balance at Jun. 30, 2018	29,139,018	4,178,368	38,476,728	(1,448)	98,279,383	(486,245)	169,585,804
Net earnings	0	0	0	0	2,013,746	0	2,013,746
Other comprehensive income, net of income tax	0	0	0	761	0	0	761
Share-based Payment Arrangement, Amount Capitalized	0	0	58,691	0	0	0	58,691
Proceeds from stock options exercised	8,298	0	7,261	0	0	0	15,559
Benefit plans funded with treasury stock	0	0	168,500	0	0	242,954	411,454
Payments to acquire treasury stock	0	0	0	0	0	(54,507)	(54,507)
Stockholders' Equity Attributable to Parent, Ending Balance at Sep. 30, 2018	29,147,316	4,178,368	38,711,180	(687)	100,293,129	(297,798)	172,031,508
Stockholders' Equity Attributable to Parent, Beginning Balance at Dec. 31, 2018	30,609,596	4,387,286	41,821,778	(2,823)	95,201,732	(206,396)	171,811,173
Net earnings	0	0	0	0	1,930,318	0	1,930,318
Other comprehensive income, net of income tax	0	0	0	820	0	0	820
Share-based Payment Arrangement, Amount Capitalized	0	0	64,704	0	0	0	64,704
Proceeds from stock options exercised	8,936	0	8,444	0	0	0	17,380
Benefit plans funded with treasury stock	0	0	295,153	0	0	42,343	337,496
Payments to acquire treasury stock	0	0	0	0	0	(112,404)	(112,404)
Stock dividends	282	(4)	489	0	(769)	0	(2)
Conversion Class C to Class A	6,560	(6,560)	0	0	0	0	0
Stockholders' Equity Attributable to Parent, Ending Balance at Mar. 31, 2019	30,625,374	4,380,722	42,190,568	(2,003)	97,131,281	(276,457)	174,049,485
Stockholders' Equity Attributable to Parent, Beginning Balance at Dec. 31, 2018	30,609,596	4,387,286	41,821,778	(2,823)	95,201,732	(206,396)	171,811,173
Net earnings							9,027,786
Other comprehensive income, net of income tax							1,281
Share-based Payment Arrangement, Amount Capitalized							195,487
Proceeds from stock options exercised							298,113
Benefit plans funded with treasury stock							578,853
Payments to acquire treasury stock							(840,301)
Stockholders' Equity Attributable to Parent, Ending Balance at Sep. 30, 2019	30,654,596	4,508,336	42,626,015	(1,542)	104,228,749	(943,764)	181,072,390
Stockholders' Equity Attributable to Parent, Beginning Balance at Mar. 31, 2019	30,625,374	4,380,722	42,190,568	(2,003)	97,131,281	(276,457)	174,049,485
Net earnings	0	0	0	0	3,480,054	0	3,480,054
Other comprehensive income, net of income tax	0	0	0	716		0	716
Share-based Payment Arrangement, Amount Capitalized	0	0	65,037	0	0	0	65,037
Proceeds from stock options exercised	20,274	0	9,519	0	0	0	29,793
Benefit plans funded with treasury stock	0	0	92,605	0	0	25,190	117,795
Payments to acquire treasury stock	0	0	0	0	0	(174,704)	(174,704)
Conversion Class C to Class A	12	(14)	2	0	0	0	0
Stockholders' Equity Attributable to Parent, Ending Balance at Jun. 30, 2019	30,645,660	4,380,708	42,357,731	(1,287)	100,611,335	(425,971)	177,568,176
Net earnings	0	0	0	0	3,617,414	0	3,617,414
Other comprehensive income, net of income tax	0	0	0	(255)	0	0	(255)
Share-based Payment Arrangement, Amount Capitalized	0	0	65,746	0	0	0	65,746
Proceeds from stock options exercised	8,936	127,628	114,376	0	0	0	250,940
Benefit plans funded with treasury stock	0	0	88,162	0	0	35,400	123,562
Payments to acquire treasury stock	0	0	0	0	0	(553,193)	(553,193)
Conversion Class C to Class A	0	0	0	0	0	0	0
Stockholders' Equity Attributable to Parent, Ending Balance at Sep. 30, 2019	$ 30,654,596	$ 4,508,336	$ 42,626,015	$ (1,542)	$ 104,228,749	$ (943,764)	$ 181,072,390