SIGNIFICANT ACCOUNTING POLICIES - Recent Accounting Pronouncements (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		9 Months Ended		12 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Jun. 30, 2017	Jun. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Stock-based compensation expense	$ 2,164	$ 2,948	$ 5,080	$ 5,425	$ 8,693	$ 7,552	$ 12,930	$ 9,763	$ 11,134
Payment of employee taxes on stock-based compensation	$ 1,338	$ 259	$ 1,339	$ 259	$ 1,367	$ 271	$ 1,477	288	2,212
ASU 2016-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Stock-based compensation expense								(300)	(2,200)
Payment of employee taxes on stock-based compensation								$ 300	$ 2,200