STOCK BASED COMPENSATION - Stock Option Plan Activity (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Number of Options
Options outstanding, beginning balance (in shares)	935
Options granted (in shares)	50
Options exercised (in shares)	(182)
Options forfeited (in shares)	(3)
Options outstanding, ending balance (in shares)	800	935
Number of options vested and exercisable (in shares)	508
Weighted Average Exercise Price
Options outstanding, beginning balance (in dollars per share)	$ 18.21
Options granted (in dollars per share)	36.22
Options exercised (in dollars per share)	17.44
Options forfeited (in dollars per share)	20.53
Options outstanding, ending balance (in dollars per share)	19.56	$ 18.21
Weighted Average Exercise Price, Options vested and exercisable (in dollars per share)	$ 17.01
Weighted Average Remaining Contractual Term, Options outstanding	5 years 10 months 17 days	6 years 2 months 23 days
Weighted Average Remaining Contractual Term, Options vested and exercisable	4 years 8 months 12 days
Aggregate Intrinsic Value, Options outstanding	$ 13,885	$ 16,773
Aggregate Intrinsic Value, Options vested and exercisable	$ 10,093