NET INCOME PER COMMON SHARE AND EQUITY PER COMMON SHARE (Details) - $ / shares	3 Months Ended		12 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
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)	9,135,000	9,066,000
Dilutive effect of employee stock options (in shares)	69,000	64,000
Weighted average common shares outstanding during the period for Diluted computation (in shares)	9,204,000	9,130,000
Common stock excluded from calculations of diluted net income per share (in shares)	0
Class A Stock [Member]
Class of Stock [Line Items]
Common stock, shares authorized (in shares)	15,000,000
Common stock, shares issued (in shares)	8,263,579	8,191,397
Common stock, shares outstanding (in shares)	8,263,579	8,191,397
Common stock, par value (in dollars per share)	$ 1.00
Common stock, shares issued during period (in shares)	17,565	15,184
Equity per common share (in dollars per share)	$ 15.38		$ 15.28
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