STOCK COMPENSATION PLANS (Details)			3 Months Ended		9 Months Ended
	May 06, 2020 $ / shares shares	May 08, 2019 $ / shares shares	Sep. 30, 2020 USD ($) $ / shares shares	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) Director $ / shares shares	Sep. 30, 2019 USD ($)
Stock Compensation Plans [Abstract]
Compensation expense					$ 134,000	$ 136,000
Number of directors in committee | Director					3
Total intrinsic value of options exercised			$ 391,000
Shares of Class A Non-Voting Common Stock under option [Abstract]
Exercised/vested and released, aggregate intrinsic value			$ 391,000
Class A Stock [Member] | Stock Options [Member]
Stock Compensation Plans [Abstract]
Total intrinsic value of options exercised					$ 391,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Outstanding at beginning of period, option shares (in shares) | shares					153,250
Granted, option shares (in shares) | shares					0
Exercised/vested and released, option shares (in shares) | shares					(25,000)
Expired/cancelled, option shares (in shares) | shares					0
Outstanding at end of period, option shares (in shares) | shares			128,250		128,250
Exercisable/vested at end of period, option share (in shares) | shares			128,250		128,250
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Outstanding at beginning of period, weighted average exercise price (in dollars per shares) | $ / shares					$ 20.40
Granted, weighted average exercise price (in dollars per share) | $ / shares					0
Exercised/vested and released, weighted average exercise price (in dollars per shares) | $ / shares					18.73
Expired/cancelled, weighted average exercise price (in dollars per share) | $ / shares					0
Outstanding at end of period, weighted average exercise price (in dollars per shares) | $ / shares			$ 20.73		20.73
Options exercisable at year end (in dollars per shares) | $ / shares			$ 20.73		$ 20.73
Shares of Class A Non-Voting Common Stock under option [Abstract]
Outstanding at end of period, weighted average remaining life					2 years 2 months 7 days
Exercisable/vested at end of period, weighted average remaining life					2 years 2 months 7 days
Outstanding at beginning of period, aggregate intrinsic value					$ 2,575,000
Granted, aggregate intrinsic value					0
Exercised/vested and released, aggregate intrinsic value					391,000
Expired/cancelled, aggregate intrinsic value					0
Outstanding at end of period, aggregate intrinsic value			$ 1,762,000		1,762,000
Exercisable/vested at end of period, aggregate intrinsic value			1,762,000		1,762,000
Class A Stock [Member] | Stock Options [Member] | 2015 Equity Compensation Plan [Member]
Stock Compensation Plans [Abstract]
Unrecognized expense related to non-vested option shares			0		0
Class A Stock [Member] | Restricted Stock [Member]
Stock Compensation Plans [Abstract]
Compensation expense			$ 44,000	$ 45,000	$ 134,000	$ 136,000
Fair value per share (in dollars per share) | $ / shares	$ 35.01	$ 36.11
Shares [Roll Forward]
Outstanding at beginning of year (in shares) | shares					5,000
Granted (in shares) | shares	5,000	5,000			5,000
Exercised/vested and released, restricted stock awards (in shares) | shares					(5,000)
Cancelled (in shares) | shares					0
Unvested Outstanding at end of year (in shares) | shares			5,000		5,000
Weighted Average Grant Date Fair Value [Abstract]
Outstanding at beginning of year (in dollars per shares) | $ / shares					$ 36.11
Granted, weighted average grant date fair value (in dollars per share) | $ / shares					35.01
Vested and released, weighted average grant date fair value (in dollars per shares) | $ / shares					36.11
Cancelled, weighted average grant date fair value (in dollars per share) | $ / shares					0
Unvested Outstanding at end of year (in dollars per shares) | $ / shares			$ 35.01		$ 35.01
Class A Stock [Member] | Restricted Stock [Member] | 2015 Equity Compensation Plan [Member]
Stock Compensation Plans [Abstract]
Unrecognized expense related to non-vested option shares			$ 104,000		$ 104,000
Period over which unvested options cost will recognized					21 days