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STOCK BASED AND DEFERRED COMPENSATION - Summary of Additional Information Regarding Stock Plan (Details) - USD ($) $ in Thousands | 9 Months Ended | 12 Months Ended
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Sep. 30, 2018 | Dec. 31, 2017
Summary of stock based compensation agreements |  |  |
Unrecognized stock-based compensation cost |  | $ 22,742 | $ 18,439
Weighted average years expense recognition period |  | 2 years 5 months 16 days | 2 years 5 months 23 days
Total stock-based awards outstanding (in shares) | [1] | 1,308,289 | 1,269,657
[1] | Includes unvested restricted stock, performance-based awards (assuming 100% payout) and restricted stock units.

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