Stock Options - Activity (Details) - USD ($)	3 Months Ended				6 Months Ended		9 Months Ended		12 Months Ended
	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020	Dec. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Mar. 31, 2021	Mar. 31, 2020	Jun. 30, 2020
2012 Employee Plan
Stock options
Outstanding, beginning of year					117,840	72,500	117,840	72,500	72,500
Granted	0		1,800				0	41,000
Exercised	(1,800)		(14,100)				(1,800)	(14,100)
Forfeited							(4,000)
Outstanding, end of period	112,040		99,400				112,040	99,400	117,840
Exercisable	44,600		36,900				44,600	36,900
Weighted average fair value at grant date of options granted								$ 15.28
Total intrinsic value of options exercised							$ 42,000	$ 255,000
Total intrinsic value of options outstanding	$ 1,735,000		$ 241,000				1,735,000	241,000
Total intrinsic value of options exercisable	$ 847,000		$ 172,000				$ 847,000	$ 172,000
Outstanding, beginning of year, weighted average exercise price					$ 18.84	$ 11.01	$ 18.84	$ 11.01	$ 11.01
Granted, weighted average exercise price								27.76
Forfeited, weighted average exercise price							8.15
Exercised, weighted average exercise price							11.39	7.57
Outstanding, end of period, weighted average exercise price	$ 19.34		$ 18.41				19.34	18.41	$ 18.84
Exercisable, end of period, weighted average exercise price	$ 15.84		$ 13.27				$ 15.84	$ 13.27
2012 Non-Employee Plan
Stock options
Outstanding, beginning of year					12,000	10,200	12,000	10,200	10,200
Granted							0	1,800
Exercised		(1,200)		(1,200)	(1,200)	(1,200)	(1,200)
Outstanding, end of period	10,800		12,000				10,800	12,000	12,000
Exercisable	7,320		5,760				7,320	5,760
Weighted average fair value at grant date of options granted								$ 12.94
Total intrinsic value of options exercised							$ 31,000
Total intrinsic value of options outstanding	$ 263,000		$ 73,000				263,000	$ 73,000
Total intrinsic value of options exercisable	$ 188,000		$ 42,000				$ 188,000	$ 42,000
Outstanding, beginning of year, weighted average exercise price					$ 10.29	$ 7.99	$ 10.29	$ 7.99	$ 7.99
Exercised, weighted average exercise price							8.70
Outstanding, end of period, weighted average exercise price	$ 10.47		$ 10.29				10.47	10.29	$ 10.29
Exercisable, end of period, weighted average exercise price	$ 9.15		$ 8.35				$ 9.15	$ 8.35
2018 Non-Employee Plan
Stock options
Outstanding, beginning of year					48,400	15,200	48,400	15,200	15,200
Granted		0			0		0	33,200
Exercised							(1,600)
Outstanding, end of period	46,800		48,400				46,800	48,400	48,400
Exercisable	20,480		12,240				20,480	12,240
Weighted average fair value at grant date of options granted								$ 15.09
Total intrinsic value of options exercised							$ 30,000
Total intrinsic value of options outstanding	$ 519,000						519,000
Total intrinsic value of options exercisable	$ 241,000						$ 241,000
Outstanding, beginning of year, weighted average exercise price					$ 23.48	$ 16.20	$ 23.48	16.20	$ 16.20
Granted, weighted average exercise price								26.82
Exercised, weighted average exercise price							16.20
Outstanding, end of period, weighted average exercise price	$ 23.73		$ 23.48				23.73	23.48	$ 23.48
Exercisable, end of period, weighted average exercise price	$ 23.08		$ 21.96				$ 23.08	$ 21.96
2020 Non-Employee Plan
Stock options
Granted							5,000
Exercised	0		0				0	0
Outstanding, end of period	5,000						5,000
Exercisable	1,000						1,000
Weighted average fair value at grant date of options granted							$ 12.20
Total intrinsic value of options outstanding	$ 60,000						$ 60,000
Total intrinsic value of options exercisable	$ 12,000						$ 12,000
Granted, weighted average exercise price							$ 22.80
Outstanding, end of period, weighted average exercise price	$ 22.80						22.80
Exercisable, end of period, weighted average exercise price	$ 22.80						$ 22.80