NET INCOME PER COMMON SHARE AND EQUITY PER COMMON SHARE (Details) - $ / shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
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)	9,277,000	9,239,000	9,175,000
Dilutive effect of employee stock options and awards (in shares)	49,000	54,000	67,000
Weighted average common shares outstanding during the period for Diluted computation (in shares)	9,326,000	9,293,000	9,242,000
Common Stock [Abstract]
Shares excluded from calculations of diluted net income per share (in shares)			0
Earnings Per Share [Abstract]
Equity per common share (in dollars per share)	$ 17.28	$ 16.53	$ 15.98
Common Stock [Member] | Class A Stock [Member]
Common Stock [Abstract]
Common stock, shares authorized (in shares)	15,000,000	15,000,000	15,000,000
Common stock, shares issued (in shares)	8,410,246	8,368,428	8,333,454
Common stock, shares outstanding (in shares)	8,410,246	8,368,428	8,333,454
Common stock, par value (in dollars per share)	$ 1
Common stock, shares issued during period (in shares)	41,818	35,574	87,421
Common Stock [Member] | Class B Stock [Member]
Common Stock [Abstract]
Common stock, shares authorized (in shares)	1,040,000	1,040,000	1,040,000
Common stock, shares issued (in shares)	881,452	881,452	881,452
Common stock, shares outstanding (in shares)	881,452	881,452	881,452
Common stock, par value (in dollars per share)	$ 1
Stock Option [Member]
Common Stock [Abstract]
Shares excluded from calculations of diluted net income per share (in shares)	0	0
Restricted Stock [Member]
Common Stock [Abstract]
Shares excluded from calculations of diluted net income per share (in shares)	5,390	3,480	3,460