ACCUMULATED OTHER COMPREHENSIVE LOSS (Components of AOCI) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Increase (Decrease) in Equity
Beginning balance	$ 1,269,813	$ 1,169,756	$ 1,188,202
Other comprehensive income (loss) before reclassifications	(11,023)	10,719	(56,647)
Amounts reclassified out of accumulated other comprehensive loss	8,180	2,667	806
Tax benefit (expense)	1,417	(66)	4,877
Other comprehensive (loss) income, net of tax	(1,426)	13,320	(50,964)
Ending balance	1,341,551	1,269,813	1,169,756
Foreign Currency Translation Adjustments
Increase (Decrease) in Equity
Beginning balance	(187,795)	(212,925)	(170,575)
Other comprehensive income (loss) before reclassifications	10,212	25,130	(47,374)
Amounts reclassified out of accumulated other comprehensive loss	0	0	0
Tax benefit (expense)	1,349	0	5,024
Other comprehensive (loss) income, net of tax	11,561	25,130	(42,350)
Ending balance	(176,234)	(187,795)	(212,925)
Unrealized (Losses) Gains on Available-for-Sale Securities
Increase (Decrease) in Equity
Beginning balance	143	(69)	(146)
Other comprehensive income (loss) before reclassifications	(10)	(70)	182
Amounts reclassified out of accumulated other comprehensive loss	0	332	0
Tax benefit (expense)	2	(50)	(105)
Other comprehensive (loss) income, net of tax	(8)	212	77
Ending balance	135	143	(69)
Unrealized Loss on Interest Rate Hedge
Increase (Decrease) in Equity
Beginning balance	(20,839)	(8,773)	0
Other comprehensive income (loss) before reclassifications	(20,970)	(14,401)	(9,579)
Amounts reclassified out of accumulated other comprehensive loss	8,180	2,335	806
Tax benefit (expense)	0	0	0
Other comprehensive (loss) income, net of tax	(12,790)	(12,066)	(8,773)
Ending balance	(33,629)	(20,839)	(8,773)
Unrealized (loss) gain on unfunded pension liability
Increase (Decrease) in Equity
Beginning balance	(1,560)	(1,604)	(1,686)
Other comprehensive income (loss) before reclassifications	(255)	60	124
Amounts reclassified out of accumulated other comprehensive loss	0	0	0
Tax benefit (expense)	66	(16)	(42)
Other comprehensive (loss) income, net of tax	(189)	44	82
Ending balance	(1,749)	(1,560)	(1,604)
Accumulated Other Comprehensive Loss
Increase (Decrease) in Equity
Beginning balance	(210,051)	(223,371)	(172,407)
Other comprehensive (loss) income, net of tax	(1,426)	13,320	(50,964)
Ending balance	$ (211,477)	$ (210,051)	$ (223,371)