NET INCOME PER COMMON SHARE AND EQUITY PER COMMON SHARE (Details) - $ / shares	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	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)	9,223,000	9,135,000
Dilutive effect of employee stock options and awards (in shares)	58,000	69,000
Weighted average common shares outstanding during the period for Diluted computation (in shares)	9,281,000	9,204,000
Class A Stock [Member]
Class of Stock [Line Items]
Common stock, shares authorized (in shares)	15,000,000
Common stock, shares issued (in shares)	8,348,243	8,263,579
Common stock, shares outstanding (in shares)	8,348,243	8,263,579
Common stock, par value (in dollars per share)	$ 1.00
Common stock, shares issued during period (in shares)	14,789	17,565
Equity per common share (in dollars per share)	$ 16.09		$ 15.98
Class B Stock [Member]
Class of Stock [Line Items]
Common stock, shares authorized (in shares)	1,040,000
Common stock, shares issued (in shares)	881,452	881,452
Common stock, shares outstanding (in shares)	881,452	881,452
Common stock, par value (in dollars per share)	$ 1.00
Restricted Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Shares excluded from calculations of diluted net income per share (in shares)	0