Stock-based compensation

6 Months Ended

Jun. 30, 2017

Stock-based compensation

Stock-based compensation

8. Stock‑based compensation

Stock options

A summary of the Company’s stock option activity and related information for the six months ended June 30, 2017 is as follows:

				Weighted-average
		Weighted-average		remaining	Aggregate
		exercise price per		contractual term	intrinsic value
	Shares	share		(years)	(in thousands)
Outstanding at December 31, 2016	5,848,470	$	6.35	8.0	$	62
Granted	1,905,000	$	1.32
Exercised	—	$	—
Forfeited/cancelled	(180,315)	$	2.31
Outstanding at June 30, 2017	7,573,155	$	5.19	8.0	$	2,939
Vested at June 30, 2017	3,921,304	$	7.74	7.1	$	694
Vested and expected to vest at June 30, 2017(1)	7,323,155	$	5.32	8.0	$	2,737

(1) This represents the number of vested options as of June 30, 2017, plus the number of unvested options expected to vest as of June 30, 2017.

The fair value of each stock option granted during the six months ended June 30, 2017 and 2016 was estimated on the grant date using the Black-Scholes option-pricing model using the following weighted-average assumptions:

	Six months ended June 30,
	2017		2016
Risk-free interest rate	2.05	%	1.47	%
Volatility	79	%	75	%
Dividend yield	—		—
Expected term (years)	6.4		5.9

In June 2016, the Company granted stock options to purchase a total of 500,000 shares of common stock to certain employees that vest only upon the achievement of specified performance conditions. The grant date fair value of these options was approximately $445,000. In October 2016, the Company determined that 50% of performance conditions had been achieved and as a result 250,000 shares vested and the Company recognized stock-based compensation expense of approximately $222,000 for the year ended December 31, 2016.  The Company determined that the remaining 50% of the performance conditions were not considered probable of achievement as of June 30, 2017 and as a result, has not recognized any stock-based compensation expense related to the remaining unvested awards.

Restricted stock units

The approximate total fair value of restricted stock units (RSUs) vested during the three and six months ended June 30, 2016 was $0 and $65,000, respectively. As of June 30, 2016, all RSUs had vested and there was no remaining unrecognized stock-based compensation expense. There were no RSUs granted during or subsequent to the three and six months ended June 30, 2016.

During the first quarter of 2013, the Company amended the terms of certain RSUs related to a total of 697,060 shares of common stock to allow for tax withholdings greater than the minimum required statutory withholding amount. As a result of this change in the terms of the awards, the outstanding RSUs were considered to be liability instruments. As a result of this modification, the Company recorded a liability for the fair value of the awards as of each reporting date with the change in fair value recorded through the statement of operations. During the three and six months ended June 30, 2016, the Company made approximate deposits with the taxing authorities of $0 and $5,000 in respect of the tax liability for awards that settled during the period.  As of June 30, 2016, the Company had no remaining tax liability related to these awards.