NET INCOME PER COMMON SHARE AND EQUITY PER COMMON SHARE (Details) - $ / shares	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Shares used in computing basic and diluted net income per share [Abstract]
Weighted average common shares outstanding during the period for Basic computation (in shares)	9,395,000	9,326,000	9,381,000	9,311,000
Dilutive effect of employee stock options and awards (in shares)	30,000	41,000	35,000	46,000
Weighted average common shares outstanding during the period for Diluted computation (in shares)	9,425,000	9,367,000	9,416,000	9,357,000
Class A Stock [Member]
Common Stock [Abstract]
Common stock, shares authorized (in shares)	15,000,000		15,000,000
Common stock, shares issued (in shares)	8,519,129	8,451,910	8,519,129	8,451,910
Common stock, shares outstanding (in shares)	8,519,129	8,451,910	8,519,129	8,451,910
Common stock, par value (in dollars per share)	$ 1.00		$ 1.00
Earnings Per Share [Abstract]
Equity per common share (in dollars per share)			$ 18.32		$ 18.16
Class B Stock [Member]
Common Stock [Abstract]
Common stock, shares authorized (in shares)	1,040,000		1,040,000
Common stock, shares issued (in shares)	881,452	881,452	881,452	881,452
Common stock, shares outstanding (in shares)	881,452	881,452	881,452	881,452
Common stock, par value (in dollars per share)	$ 1.00		$ 1.00
Restricted Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Abstract]
Shares excluded from calculations of diluted net income per share (in shares)	0	0	0	0