ACCUMULATED OTHER COMPREHENSIVE LOSS - Schedule of Accumulated Other Comprehensive Loss (Details) - USD ($)		3 Months Ended
		Mar. 31, 2019	Mar. 31, 2018
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
BALANCE		$ 690,506,000	$ 659,054,000
Other comprehensive gain (loss) before reclassification		80,000	74,000
Reclassification to net income	[1]	634,000	422,000
TOTAL OTHER COMPREHENSIVE INCOME		714,000	496,000
BALANCE		716,201,000	642,649,000
Unrealized gain (loss) on available-for-sale securities [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
BALANCE		10,000	(258,000)
Other comprehensive gain (loss) before reclassification		47,000	54,000
TOTAL OTHER COMPREHENSIVE INCOME		47,000	54,000
BALANCE		57,000	(204,000)
Net unrealized gain (loss) on retirement plan [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
BALANCE	[2]	(16,198,000)	(11,169,000)
Reclassification to net income	[1],[2]	634,000	422,000
TOTAL OTHER COMPREHENSIVE INCOME	[2]	634,000	422,000
BALANCE	[2]	(15,564,000)	(10,747,000)
Change in cumulative foreign currency translation adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
BALANCE		(46,000)	(37,000)
Other comprehensive gain (loss) before reclassification		33,000	20,000
TOTAL OTHER COMPREHENSIVE INCOME		33,000	20,000
BALANCE		(13,000)	(17,000)
Accumulated Other Comprehensive Loss [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
BALANCE		(16,234,000)	(11,464,000)
TOTAL OTHER COMPREHENSIVE INCOME		714,000	496,000
BALANCE		$ (15,520,000)	$ (10,968,000)

[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 $634,000 and $422,000 for the three months ended March 31, 2019 and 2018, respectively.

[2] Refer to Note 14: Supplemental Executive Retirement Plan