ACCUMULATED OTHER COMPREHENSIVE LOSS - Changes in Accumulated Other Comprehensive Loss by Component (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2020
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance beginning of period	$ 1,409,587	$ 1,348,450	$ 1,341,551	$ 1,253,971	$ 1,205,805	$ 1,269,813	$ 1,341,551	$ 1,269,813
Other comprehensive income (loss) before reclassifications							3,250
Amounts reclassified out of accumulated other comprehensive loss							7,474
Tax benefit							37
Other comprehensive (loss) income, net of tax	(11,827)	10,640	11,948	12,385	17,528	(59,306)	10,761	(29,393)
Balance ending of period	1,463,560	1,409,587	1,348,450	1,304,715	1,253,971	1,205,805	1,463,560	1,304,715
Foreign Currency Translation
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance beginning of period			(176,234)				(176,234)
Other comprehensive income (loss) before reclassifications							767
Amounts reclassified out of accumulated other comprehensive loss							0
Tax benefit							0
Other comprehensive (loss) income, net of tax							767
Balance ending of period	(175,467)						(175,467)
Unrealized Gains (Losses) on Available-For-Sale Securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance beginning of period			135				135
Other comprehensive income (loss) before reclassifications							(177)
Amounts reclassified out of accumulated other comprehensive loss							0
Tax benefit							37
Other comprehensive (loss) income, net of tax							(140)
Balance ending of period	(5)						(5)
Unrealized (Losses) Gains on Interest Rate Hedge
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance beginning of period			(33,629)				(33,629)
Other comprehensive income (loss) before reclassifications							2,660
Amounts reclassified out of accumulated other comprehensive loss							7,474
Tax benefit							0
Other comprehensive (loss) income, net of tax							10,134
Balance ending of period	(23,495)						(23,495)
Unrealized Losses on Unfunded Pension Liability
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance beginning of period			(1,749)				(1,749)
Other comprehensive income (loss) before reclassifications							0
Amounts reclassified out of accumulated other comprehensive loss							0
Tax benefit							0
Other comprehensive (loss) income, net of tax							0
Balance ending of period	(1,749)						(1,749)
Total
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance beginning of period	(188,889)	(199,529)	(211,477)	(251,829)	(269,357)	(210,051)	(211,477)	(210,051)
Other comprehensive (loss) income, net of tax	(11,827)	10,640	11,948	12,385	17,528	(59,306)
Balance ending of period	$ (200,716)	$ (188,889)	$ (199,529)	$ (239,444)	$ (251,829)	$ (269,357)	$ (200,716)	$ (239,444)