COMPREHENSIVE INCOME - Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2019	Dec. 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)
Other comprehensive income (loss) before reclassifications	12,034	17,320
Reclassified from AOCI to net income (loss)	1,521	(3,454)
Derivative financial instruments reclassified to advanced billings on contracts	(197)
Amounts reclassified from AOCI to advanced billings on contracts (3)		(2,831)
Net other comprehensive income (loss)	13,358	10,997
Stockholders' equity, ending balance	(294,939)	(277,297)
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)
Stockholders' equity, ending balance	1,926	(11,432)
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	13,401	16,452
Reclassified from AOCI to net income (loss)	3,176	551
Derivative financial instruments reclassified to advanced billings on contracts	0
Amounts reclassified from AOCI to advanced billings on contracts (3)		0
Net other comprehensive income (loss)	16,577	17,003
Stockholders' equity, ending balance	5,743	(10,834)
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	0	38
ASU 2016-1 cumulative adjustment			(38)
Other comprehensive income (loss) before reclassifications	0	0
Reclassified from AOCI to net income (loss)	0	0
Derivative financial instruments reclassified to advanced billings on contracts	0
Amounts reclassified from AOCI to advanced billings on contracts (3)		0
Net other comprehensive income (loss)	0	(38)
Stockholders' equity, ending balance	0	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	(1,367)	890
Reclassified from AOCI to net income (loss)	202	(1,265)
Derivative financial instruments reclassified to advanced billings on contracts	(197)
Amounts reclassified from AOCI to advanced billings on contracts (3)		0
Net other comprehensive income (loss)	(1,362)	(375)
Stockholders' equity, ending balance	0	1,362
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	(22)
Reclassified from AOCI to net income (loss)	(1,857)	(2,740)
Derivative financial instruments reclassified to advanced billings on contracts	0
Amounts reclassified from AOCI to advanced billings on contracts (3)		(2,831)
Net other comprehensive income (loss)	(1,857)	(5,593)
Stockholders' equity, ending balance	$ (3,817)	$ (1,960)

Other Comprehensive Income (Loss), Cash Flow Hedge, Advance Billings On Contracts, Reclassification, Net Of Tax

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Other Comprehensive Income (Loss), Net Of Tax, Including Adjustments Made For Accounting Standards Updates

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Reclassification From Accumulated Other Comprehensive Income To Pensions, Current Period, Net Of Tax

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Amount of cumulative effect of the change in accounting principle or new accounting pronouncement on retained earnings or other components of equity or net assets in the statement of financial position as of the beginning of the earliest period presented.

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Amount after tax, before reclassification adjustments of other comprehensive income (loss).

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Amount after tax and reclassification adjustments of other comprehensive income (loss).

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Amount after tax of reclassification adjustments of other comprehensive income (loss).

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Amount of stockholders' equity (deficit), net of receivables from officers, directors, owners, and affiliates of the entity, attributable to both the parent and noncontrolling interests. Amount excludes temporary equity. Alternate caption for the concept is permanent equity.

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