EQUITY - Changes in Shareholders' Equity (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Balance at beginning of period	$ 134,908
Exercise of common stock options	$ 94
Exercise of common stock options, shares	20,653
Issuance for employee stock purchase plan	$ 673
Issuance for employee stock purchase plan, shares	66,785
Shares withheld for employee taxes upon vesting of restricted stock units	$ (51)
Stock-based compensation expense	1,821
Net loss	(23,078)	$ (15,653)
Balance at end of period	114,367
Common Stock
Balance at beginning of period	$ 29
Balance at beginning of year, shares	29,364,100
Exercise of common stock options, shares	20,653
Issuance for employee stock purchase plan, shares	66,785
Shares withheld for employee taxes upon vesting of restricted stock units, shares	(3,416)
Vesting of restricted stock units, shares	10,435
Balance at end of period	$ 29
Balance at end of year, shares	29,458,557
Additional Paid-In Capital
Balance at beginning of period	$ 358,063
Exercise of common stock options	94
Issuance for employee stock purchase plan	673
Shares withheld for employee taxes upon vesting of restricted stock units	(51)
Stock-based compensation expense	1,821
Balance at end of period	360,600
Accumulated Deficit
Balance at beginning of period	(223,184)
Net loss	(23,078)
Balance at end of period	$ (246,262)