STOCK-BASED COMPENSATION - Adoption of ASU No. 2016-09 (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Jan. 01, 2017
Prospective adoption
Provision for income taxes	$ (2,952)	$ (4,059)	$ (6,749)	$ (10,749)
ASU 2016-09
Prospective adoption
Provision for income taxes	$ 115	$ 122	$ 744	$ 463
Increase of basic and diluted earnings per share	$ 0.01	$ 0.01	$ 0.04	$ 0.03
Cumulative effect adjustment to retained earnings					$ 0

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.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 250
-SubTopic 10
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
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-Name Accounting Standards Codification
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Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
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-Name Accounting Standards Codification
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