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NET INCOME PER COMMON SHARE AND EQUITY PER COMMON SHARE (Details) - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	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)	9,239,000	9,175,000	9,098,000
Dilutive effect of employee stock options and awards (in shares)	54,000	67,000	63,000
Weighted average common shares outstanding during the period for Diluted computation (in shares)	9,293,000	9,242,000	9,161,000
Earnings Per Share [Abstract]
Equity per common share (in dollars per share)	$ 16.53	$ 15.98	$ 15.28
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)	8,369,028	8,333,454	8,246,033
Common stock, shares outstanding (in shares)	8,369,028	8,333,454	8,246,033
Common stock, par value (in dollars per share)	$ 1.00
Common stock, shares issued during period (in shares)	35,574	87,421	69,820
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)	$ 1.00
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)	3,480	3,460

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Total number of common shares of an entity that have been sold or granted to shareholders (excludes common shares that were issued, repurchased and remain in the treasury). These shares represent capital invested by the firm's shareholders and owners, and may be all or only a portion of the number of shares authorized. Shares issued include shares outstanding.

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Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented.

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Face amount or stated value per share of common stock.

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The amount of net income or loss for the period per each share in instances when basic and diluted earnings per share are the same amount and reported as a single line item on the face of the financial statements. Basic earnings per share is the amount of net income or loss for the period per each share of common stock or unit outstanding during the reporting period. Diluted earnings per share includes the amount of net income or loss for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

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Additional shares included in the calculation of diluted EPS as a result of the potentially dilutive effect of share based payment arrangements using the treasury stock method.

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