COMPREHENSIVE INCOME - Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Jan. 01, 2018
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Stockholders' equity, beginning balance	$ (277,297)	$ 190,703
ASU 2016-1 cumulative adjustment			$ (38)
Reclassified from AOCI to net income (loss)	(132)	(3,700)
Net other comprehensive income (loss)	8,950	692
Net other comprehensive income (loss)		654
Stockholders' equity, ending balance	(317,852)	69,996
Accumulated Other Comprehensive (Loss) Income
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Stockholders' equity, beginning balance	(11,432)	(22,429)
Other comprehensive income (loss) before reclassifications	9,082	4,392
Stockholders' equity, ending balance	(2,482)	(21,775)
Currency translation (loss) gain
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Stockholders' equity, beginning balance	(10,834)	(27,837)
ASU 2016-1 cumulative adjustment			0
Other comprehensive income (loss) before reclassifications	10,260	3,223
Reclassified from AOCI to net income (loss)	0	(2,044)
Net other comprehensive income (loss)	10,260
Net other comprehensive income (loss)		1,179
Stockholders' equity, ending balance	(574)	(26,658)
Net unrealized gain (loss) on investments (net of tax)
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Stockholders' equity, beginning balance		38
ASU 2016-1 cumulative adjustment			(38)
Other comprehensive income (loss) before reclassifications		0
Reclassified from AOCI to net income (loss)		0
Net other comprehensive income (loss)		(38)
Stockholders' equity, ending balance		0
Net unrealized gain (loss) on derivative instruments
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Stockholders' equity, beginning balance	1,362	1,737
ASU 2016-1 cumulative adjustment			0
Other comprehensive income (loss) before reclassifications	(1,178)	1,224
Reclassified from AOCI to net income (loss)	224	(1,272)
Net other comprehensive income (loss)	(954)
Net other comprehensive income (loss)		(48)
Stockholders' equity, ending balance	408	1,689
Net unrecognized gain (loss) related to benefit plans (net of tax)
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Stockholders' equity, beginning balance	(1,960)	3,633
ASU 2016-1 cumulative adjustment			$ 0
Other comprehensive income (loss) before reclassifications	0	(55)
Reclassified from AOCI to net income (loss)	(356)	(384)
Net other comprehensive income (loss)	(356)
Net other comprehensive income (loss)		(439)
Stockholders' equity, ending balance	$ (2,316)	$ 3,194