ACCUMULATED OTHER COMPREHENSIVE LOSS - Schedule of Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
BALANCE		$ 991,616	$ 839,770	$ 912,714	$ 811,449
Other comprehensive gain (loss) before reclassification				(259)	313
Reclassification to net income	[1]			3,500	1,917	[2]
TOTAL OTHER COMPREHENSIVE INCOME (LOSS)		1,016	14	3,263	2,230
BALANCE		1,036,322	879,636	1,036,322	879,636
Unrealized gain (loss) on available-for-sale securities [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
BALANCE				91	191
Other comprehensive gain (loss) before reclassification				(35)	342
TOTAL OTHER COMPREHENSIVE INCOME (LOSS)				(35)	342
BALANCE		56	533	56	533
Net unrealized gain (loss) on retirement plan [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
BALANCE	[2]			(36,075)	(17,167)
Reclassification to net income	[1],[2]			3,522
TOTAL OTHER COMPREHENSIVE INCOME (LOSS)	[2]			3,522	1,917
BALANCE	[2]	(32,553)	(15,250)	(32,553)	(15,250)
Change in cumulative foreign currency translation adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
BALANCE				(35)	(21)
Other comprehensive gain (loss) before reclassification				(224)	(29)
TOTAL OTHER COMPREHENSIVE INCOME (LOSS)				(224)	(29)
BALANCE		(259)	(50)	(259)	(50)
Accumulated Other Comprehensive Loss [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
BALANCE		(33,772)	(14,781)	(36,019)	(16,997)
Reclassification to net income	[1]			3,522
TOTAL OTHER COMPREHENSIVE INCOME (LOSS)		1,016	14	3,263	2,230
BALANCE		$ (32,756)	$ (14,767)	$ (32,756)	$ (14,767)

[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 $3.5 million and $1.9 million for the nine months ended September 30, 2021 and 2020, respectively.

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