Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2017

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Summary of Share Based Fair Value Assumptions

The fair value of options granted were estimated using the Black-Scholes-Merton option pricing model based on the assumptions in the table below:

	Years ended December 31,
	2017		2016		2015
Expected dividend yield		0%		0%		0%
Expected volatility	70% - 72%		47%		45% - 56%
Risk-free interest rate	1.84% - 2.29%		1.13% - 2.09%		1.44% - 1.95%
Expected life (in years)	5.5 - 6.3		5.5 - 6.3		5.5 - 6.3

Schedule of Stock Option Activity

The following table summarizes the Company’s stock option activity, including grants to non-employees, for the year ended December 31, 2017:

						Weighted-
						Average
				Weighted-		Remaining
	Number of			Average		Contractual
	Shares			Exercise Price		Term (Years)
Options outstanding at December 31, 2016		12,488,551		$	2.66		8.08
Granted		4,746,250			1.25
Forfeited		(574,773	)		2.35
Cancelled		(227,419	)		4.16
Exercised		(738,934	)		0.59
Options outstanding at December 31, 2017		15,693,675		$	2.32		7.78

Schedule of Stock Options Outstanding

The following table summarizes information about stock options outstanding at December 31, 2017:

					Weighted
					Average
			Weighted		Remaining
	Number of		Average		Contractual
	Shares		Exercise Price		Term (Years)
Exercisable at December 31, 2017		7,113,007	$	2.78		6.78
Vested or expected to vest at December 31, 2017		15,195,280	$	2.34		7.75