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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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