ACCUMULATED OTHER COMPREHENSIVE LOSS - Schedule of Accumulated Other Comprehensive Loss (Details) - USD ($)		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
BALANCE		$ 659,054,000
Other comprehensive gain (loss) before reclassification		74,000	$ 15,000
Reclassification to net income	[1]	422,000	299,000
TOTAL OTHER COMPREHENSIVE INCOME		496,000	314,000
BALANCE		642,649,000
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		54,000	(15,000)
TOTAL OTHER COMPREHENSIVE INCOME		54,000	(15,000)
BALANCE		(204,000)	(261,000)
Net unrealized gain (loss) on retirement plan [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
BALANCE	[2]	(11,169,000)	(10,355,000)
Reclassification to net income	[1],[2]	422,000	299,000
TOTAL OTHER COMPREHENSIVE INCOME	[2]	422,000	299,000
BALANCE	[2]	(10,747,000)	(10,056,000)
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		20,000	30,000
TOTAL OTHER COMPREHENSIVE INCOME		20,000	30,000
BALANCE		(17,000)	(35,000)
Accumulated Other Comprehensive Loss [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
BALANCE		(11,464,000)	(10,666,000)
TOTAL OTHER COMPREHENSIVE INCOME		496,000
BALANCE		$ (10,968,000)	$ (10,352,000)

[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 $422,000 and $299,000 for the three months ended March 31, 2018 and 2017, respectively.

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