COMPREHENSIVE INCOME - Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Stockholders' equity, beginning balance	$ (323,650)	$ (294,939)	$ (317,852)	$ (277,297)	$ (294,939)	$ (277,297)
Other comprehensive income (loss) before reclassifications	(4,095)	2,380	(8,168)	9,082
Reclassified from AOCI to net income (loss)	(246)	(246)	2,640	(132)
Net other comprehensive income (loss)	(4,341)	2,134	(5,528)	8,950	(2,207)	3,422
Stockholders' equity, ending balance	(338,700)	(323,650)	(343,035)	(317,852)	(338,700)	(343,035)
Accumulated Other Comprehensive Income (Loss)
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Stockholders' equity, beginning balance	4,060	1,926	(2,482)	(11,432)	1,926	(11,432)
Stockholders' equity, ending balance	(281)	4,060	(8,010)	(2,482)	(281)	(8,010)
Currency translation (loss) gain
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Stockholders' equity, beginning balance	8,123	5,743	(574)	(10,834)	5,743	(10,834)
Other comprehensive income (loss) before reclassifications	(4,095)	2,380	(7,979)	10,260
Reclassified from AOCI to net income (loss)	0	0	3,176	0
Net other comprehensive income (loss)	(4,095)	2,380	(4,803)	10,260
Stockholders' equity, ending balance	4,028	8,123	(5,377)	(574)	4,028	(5,377)
Net unrealized gain (loss) on derivative instruments
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Stockholders' equity, beginning balance			408	1,362		1,362
Other comprehensive income (loss) before reclassifications			(189)	(1,178)
Reclassified from AOCI to net income (loss)			(22)	224
Net other comprehensive income (loss)			(211)	(954)
Stockholders' equity, ending balance			197	408		197
Net unrecognized loss related to benefit plans (net of tax)
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Stockholders' equity, beginning balance	(4,063)	(3,817)	(2,316)	(1,960)	(3,817)	(1,960)
Other comprehensive income (loss) before reclassifications	0	0	0	0
Reclassified from AOCI to net income (loss)	(246)	(246)	(514)	(356)
Net other comprehensive income (loss)	(246)	(246)	(514)	(356)
Stockholders' equity, ending balance	$ (4,309)	$ (4,063)	$ (2,830)	$ (2,316)	$ (4,309)	$ (2,830)