STOCK-BASED COMPENSATION (Tables)

3 Months Ended

Mar. 31, 2017

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Schedule of weighted average assumptions used to estimate fair value of each service-based stock option grant

The fair value of each service-based stock option grant for the reported periods is estimated on the date of the grant using the Black-Scholes option-pricing model using the weighted average assumptions noted in the following table.

	Three Months Ended March 31,
Service-Based Stock Options	2017		2016
Expected dividend rate	—	%	—	%
Expected stock price volatility	81.3 – 88.2%		78.7 – 85.5%
Risk-free interest rate	2 – 2.3%		1.3 – 1.8%
Expected life (years)	6.1 – 6.3		6.1 – 6.3

Summary of activity for service-based stock options

The following table summarizes the activity for service-based stock options for the indicated periods:

Service-Based Stock Options	Options	Weighted Average Exercise Price		Weighted Average Remaining Contractual Term (Years)	Aggregate Intrinsic Value
Outstanding at December 31, 2016	3,355,692	$	4.66	8.2	$	610
Granted	892,390	$	2.83
Exercised	390	$	2.11		$	—
Expired	5,274	$	3.03
Forfeited	75,828	$	3.46
Outstanding at March 31, 2017	4,166,590	$	4.29	8.3	$	484
Exercisable at March 31, 2017	1,548,762	$	6.51	7.3	$	107