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NET INCOME PER COMMON SHARE AND EQUITY PER COMMON SHARE (Details) - $ / shares
 12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
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) 8,960,000 8,884,000 8,774,000
Dilutive effect of employee stock options (in shares) 45,000 42,000 62,000
Weighted average common shares outstanding during the period for Diluted computation (in shares) 9,005,000 8,926,000 8,836,000
Common stock excluded from calculations of diluted net income per share (in shares) 0 67,500  
Class of Stock [Line Items]      
Equity per common share (in dollars per share) $ 14.77 $ 14.14 $ 13.89
Common Stock [Member] | Class A Stock [Member]      
Class of Stock [Line Items]      
Common stock, shares authorized (in shares) 15,000,000 15,000,000 15,000,000
Common stock, shares issued (in shares) 8,176,213 8,030,677 7,948,569
Common stock, shares outstanding (in shares) 8,176,213 8,030,677 7,948,569
Common stock, par value (in dollars per share) $ 1    
Common stock, shares issued during period (in shares) 145,536 82,108 119,733
Common Stock [Member] | Class B Stock [Member]      
Class of Stock [Line Items]      
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