EQUITY - Changes in Shareholders' Equity (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Balance at beginning of period			$ 134,908
Exercise of common stock options			$ 415
Exercise of common stock options, shares			127,507
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			3,767
Net loss	$ (21,121)	$ (24,520)	(44,199)	$ (40,172)
Balance at end of period	95,513		95,513
Common Stock
Balance at beginning of period			$ 29
Balance at beginning of year, shares			29,364,100
Exercise of common stock options			$ 1
Exercise of common stock options, shares			127,507
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	$ 30		$ 30
Balance at end of year, shares	29,565,411		29,565,411
Additional Paid-In Capital
Balance at beginning of period			$ 358,063
Exercise of common stock options			414
Issuance for employee stock purchase plan			673
Shares withheld for employee taxes upon vesting of restricted stock units			(51)
Stock-based compensation expense			3,767
Balance at end of period	$ 362,866		362,866
Accumulated Deficit
Balance at beginning of period			(223,184)
Net loss			(44,199)
Balance at end of period	$ (267,383)		$ (267,383)