STOCK-BASED COMPENSATION (Tables)

6 Months Ended

Jun. 30, 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.

	Six Months Ended June 30,
Service-Based Stock Options	2017		2016
Expected dividend rate	—	%	—	%
Expected stock price volatility	80.1 – 88.2%		78.7 – 92.2%
Risk-free interest rate	1.88 – 2.31%		1.2 – 1.8%
Expected life (years)	5.5 – 6.3		5.5 – 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	1,550,560	$	2.75
Exercised	2,152	$	2.71		$	1
Expired	84,889	$	18.52
Forfeited	137,599	$	3.38
Outstanding at June 30, 2017	4,681,612	$	3.82	8.4	$	2,038
Exercisable at June 30, 2017	1,769,955	$	5.33	7.5	$	541