INCOME TAXES - Changes in Valuation Allowance (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Valuation Allowance [Roll Forward]
Valuation allowance at beginning of period	$ 24,786	$ 8,675
Increase to valuation allowance attributable to:
Current year loss	17,484	16,111
Valuation allowance at end of period	$ 42,270	$ 24,786