STOCK COMPENSATION PLANS (Details)			3 Months Ended		6 Months Ended
	May 08, 2019 $ / shares shares	May 02, 2018 $ / shares shares	Jun. 30, 2019 USD ($) $ / shares shares	Jun. 30, 2018 USD ($)	Jun. 30, 2019 USD ($) Director $ / shares shares	Jun. 30, 2018 USD ($)
Stock Compensation Plans [Abstract]
Number of directors in committee | Director					3
Class A Stock [Member] | Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Outstanding at beginning of period, option shares (in shares) | shares					168,750
Granted, option shares (in shares) | shares					0
Exercised/vested and released, option shares (in shares) | shares					(13,500)
Expired/cancelled, option shares (in shares) | shares					0
Outstanding at end of period, option shares (in shares) | shares			155,250		155,250
Exercisable/vested at end of period, option share (in shares) | shares			155,250		155,250
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)					$ 20.11
Granted, weighted average exercise price (in dollars per share)					0
Exercised/vested and released, weighted average exercise price (in dollars per shares)					16.94
Expired/cancelled, weighted average exercise price (in dollars per share)					0
Outstanding at end of period, weighted average exercise price (in dollars per shares)			$ 20.38		20.38
Options exercisable at year end (in dollars per shares)			$ 20.38		$ 20.38
Shares of Class A Non-Voting Common Stock under option [Abstract]
Outstanding at end of period, weighted average remaining life					3 years 14 days
Exercisable/vested at end of period, weighted average remaining life					3 years 14 days
Outstanding at beginning of period, aggregate intrinsic value | $					$ 2,491,000
Granted, aggregate intrinsic value | $					0
Exercised/vested and released, aggregate intrinsic value | $					297,000
Expired/cancelled, aggregate intrinsic value | $					0
Outstanding at end of period, aggregate intrinsic value | $			$ 2,606,000		2,606,000
Exercisable/vested at end of period, aggregate intrinsic value | $			2,606,000		2,606,000
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 | $			$ 43,000	$ 48,000	$ 90,000	$ 95,000
Fair value per share (in dollars per share)	$ 36.11	$ 38.51
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)					$ 38.51
Granted, weighted average grant date fair value (in dollars per share)					36.11
Vested and released, weighted average grant date fair value (in dollars per shares)					38.51
Cancelled, weighted average grant date fair value (in dollars per share)					0
Unvested Outstanding at end of year (in dollars per shares)			$ 36.11		$ 36.11
Class A Stock [Member] | Restricted Stock [Member] | 2015 Equity Compensation Plan [Member]
Stock Compensation Plans [Abstract]
Unrecognized expense related to non-vested option shares | $			$ 154,000		$ 154,000
Period over which unvested options cost will recognized					10 months 6 days