ACCUMULATED OTHER COMPREHENSIVE LOSS - Schedule of Accumulated Other Comprehensive Loss (Details) - USD ($)		3 Months Ended		6 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
BALANCE				$ 659,054,000
Other comprehensive gain (loss) before reclassification				169,000	$ 115,000
Actuarial gain (loss)					(1,662,000)
Reclassification to net income	[1]			844,000	642,000
TOTAL OTHER COMPREHENSIVE INCOME (LOSS)		$ 517,000	$ (1,219,000)	1,013,000	(905,000)
BALANCE		650,681,000		650,681,000
Unrealized gain (loss) on available-for-sale securities [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
BALANCE				(258,000)	(246,000)
Other comprehensive gain (loss) before reclassification				171,000	90,000
TOTAL OTHER COMPREHENSIVE INCOME (LOSS)				171,000	90,000
BALANCE		(87,000)	(156,000)	(87,000)	(156,000)
Net unrealized gain (loss) on retirement plan [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
BALANCE	[2]			(11,169,000)	(10,355,000)
Actuarial gain (loss)	[2]				(1,662,000)
Reclassification to net income	[1],[2]			844,000	642,000
TOTAL OTHER COMPREHENSIVE INCOME (LOSS)	[2]			844,000	(1,020,000)
BALANCE	[2]	(10,325,000)	(11,375,000)	(10,325,000)	(11,375,000)
Change in cumulative foreign currency translation adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
BALANCE				(37,000)	(65,000)
Other comprehensive gain (loss) before reclassification				(2,000)	25,000
TOTAL OTHER COMPREHENSIVE INCOME (LOSS)				(2,000)	25,000
BALANCE		(39,000)	(40,000)	(39,000)	(40,000)
Accumulated Other Comprehensive Loss [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
BALANCE				(11,464,000)	(10,666,000)
TOTAL OTHER COMPREHENSIVE INCOME (LOSS)				1,013,000
BALANCE		$ (10,451,000)	$ (11,571,000)	$ (10,451,000)	$ (11,571,000)

[1] The Company reclassified amortization of prior service cost and actuarial loss for its retirement plan from accumulated other comprehensive loss to net income of $844,000 and $642,000 for the six months ended June 30, 2018 and 2017, respectively.

[2] Refer to Note 12: Supplemental Executive Retirement Plan.