STOCK BASED COMPENSATION (Tables)

9 Months Ended

Sep. 30, 2017

STOCK BASED COMPENSATION

Summary of stock-based compensation included in statement of operations

	Three months ended				Nine months ended
	September 30,				September 30,
	2017		2016		2017		2016
Research and development expenses	$	222	$	171	$	673	$	474
Selling, general and administrative expenses		1,878		1,470		5,194		3,663
Total stock-based compensation expense	$	2,100	$	1,641	$	5,867	$	4,137

Summary of restricted stock awards activity

		Weighted-Average
		Purchase Price
	Shares	per Share
Unvested at December 31, 2016	43,265	$	5.73
Granted	—		—
Vested	(24,336)		5.73
Unvested at September 30, 2017 (1)	18,929	$	5.73

(1)Excludes 25,657 shares of unvested restricted stock remaining from the early exercise of stock options as of September 30, 2017.

Summary of restricted stock units activity

		Weighted-Average
	Shares	Grant Date Fair Value
Outstanding at December 31, 2016	41,741	$	16.15
Granted	211,018		12.45
Settled	(14,757)		16.15
Forfeited	(19,130)		15.52
Outstanding at September 30, 2017	218,872	$	12.64

Summary of stock option activity

				Weighted-
			Weighted-	Average
			Average	Remaining		Aggregate
			Exercise Price	Contractual		Intrinsic
	Shares		per Share	Term (in years)		Value
Outstanding at December 31, 2016	2,326,801	$	13.07	8.7	$	7,927
Granted	1,261,373		12.06
Exercised	(131,755)		3.25
Cancelled	(399,465)		13.62
Outstanding at September 30, 2017	3,056,954	$	13.00	8.6	$	3,604
Exercisable at September 30, 2017	940,101	$	12.80	7.8	$	1,727
Vested and expected to vest at September 30, 2017	2,909,114	$	13.08	8.5	$	3,571

Schedule of weighted-average assumptions used in Black-Scholes option-pricing model

	Nine months ended September 30,
	2017		2016
Risk-free interest rate	2.0	%	1.5	%
Volatility	71	%	77	%
Expected term (years)	6.01		6.02
Expected dividend yield	—	%	—	%