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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - AOCI (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accumulated other comprehensive income (loss)
Beginning Balance	$ 695,387
Adjust funded status of pension plan, net of tax of $0.6, $0.7 and $0.7 million for the years December 31, 2018, 2017 and 2016 respectively	(445)	$ (840)	$ 1,357
Foreign currency translation adjustment	(1,041)	(4,390)	1,265
Reclassifications of gains on sale of marketable securities to net income			(1,044)
Adoption of ASU 2016-09			2,636	$ 155
Ending Balance	676,122	695,387
Adjust funded status of pension plan, tax	100	600	700
Accumulated Other Comprehensive Income/(Loss)
Accumulated other comprehensive income (loss)
Beginning Balance	(1,609)	3,746	1,728
Adjust funded status of pension plan, net of tax of $0.6, $0.7 and $0.7 million for the years December 31, 2018, 2017 and 2016 respectively	(445)	(840)	1,357
Foreign currency translation adjustment	(1,041)	(4,390)	1,265
Reclassifications of gains on sale of marketable securities to net income			(1,044)
Adoption of ASU 2016-09			(203)
Unrealized gain on marketable securities	(187)	78	440
Ending Balance	(3,282)	(1,609)	3,746
Pension and other postretirement benefit plans
Accumulated other comprehensive income (loss)
Beginning Balance	2,287	3,127	1,770
Adjust funded status of pension plan, net of tax of $0.6, $0.7 and $0.7 million for the years December 31, 2018, 2017 and 2016 respectively	(445)	(840)	1,357
Ending Balance	1,842	2,287	3,127
Translation Adjustment
Accumulated other comprehensive income (loss)
Beginning Balance	(4,035)	355	(910)
Foreign currency translation adjustment	(1,041)	(4,390)	1,265
Ending Balance	(5,076)	(4,035)	355
Investment
Accumulated other comprehensive income (loss)
Beginning Balance	139	264	868
Reclassifications of gains on sale of marketable securities to net income			(1,044)
Adoption of ASU 2016-09			(203)
Unrealized gain on marketable securities	(187)	78	440
Ending Balance	$ (48)	$ 139	$ 264

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Amount after tax and reclassification adjustments of gain (loss) on foreign currency translation adjustments, foreign currency transactions designated and effective as economic hedges of a net investment in a foreign entity and intra-entity foreign currency transactions that are of a long-term-investment nature.

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