STOCK-BASED COMPENSATION - Stock Option Activity (Details) - Stock options	12 Months Ended
	Dec. 31, 2018 USD ($) $ / shares shares
Shares
Stock Option Shares outstanding at beginning of period (in shares) | shares	1,990,471
Stock Option Shares granted (in shares) | shares	499,301
Stock Option Shares exercised (in shares) | shares	(159,575)
Stock Option Shares forfeited (in shares) | shares	(93,333)
Stock Option Shares outstanding at end of period (in shares) | shares	2,236,864
Stock Option Shares exercisable at end of period (in shares) | shares	970,552
Weighted-Average Exercise Price
Stock Option Shares outstanding at beginning of period (in dollars per share) | $ / shares	$ 21.09
Stock Option Shares granted (in dollars per share) | $ / shares	42.41
Stock Option Shares exercised (in dollars per share) | $ / shares	14.75
Stock Option Shares forfeited (in dollars per share) | $ / shares	23.46
Stock Option Shares outstanding at end of period (in dollars per share) | $ / shares	26.21
Stock Option Shares exercisable at end of period (in dollars per share) | $ / shares	$ 15.72
Weighted Average Remaining Contractual Term
Stock Option Shares outstanding at end of period	7 years 3 months 18 days
Stock Option Shares exercisable at end of period	5 years 1 month 6 days
Aggregate Intrinsic Value
Stock Option Shares outstanding at end of period (in dollars) | $	$ 30,294,694
Stock Option Shares exercisable at end of period (in dollars) | $	$ 21,881,342