Stock-Based Compensation (Details 2)	9 Months Ended
	Sep. 30, 2018 $ / shares shares
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Stock options outstanding (in shares) | shares	4,395,344
Weighted average exercise price (in dollars per share)	$ 4.78
Weighted average remaining contractual life	6 years 1 month 13 days
Stock options exercisable (in shares) | shares	3,247,214
Weighted average exercise price (in dollars per share)	$ 4.74
$0.55 - $1.50
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of exercise prices (in dollars per share)	0.79
Range of exercise prices (in dollars per share)	$ 1.50
Stock options outstanding (in shares) | shares	1,510,000
Weighted average exercise price (in dollars per share)	$ 1.06
Weighted average remaining contractual life	3 years 4 months 17 days
Stock options exercisable (in shares) | shares	1,510,000
Weighted average exercise price (in dollars per share)	$ 1.06
$1.51 - $5.50
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of exercise prices (in dollars per share)	1.51
Range of exercise prices (in dollars per share)	$ 5.50
Stock options outstanding (in shares) | shares	898,207
Weighted average exercise price (in dollars per share)	$ 3.22
Weighted average remaining contractual life	8 years 4 months 6 days
Stock options exercisable (in shares) | shares	196,666
Weighted average exercise price (in dollars per share)	$ 2.72
$5.51 - $10.67
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of exercise prices (in dollars per share)	5.51
Range of exercise prices (in dollars per share)	$ 10.67
Stock options outstanding (in shares) | shares	1,987,137
Weighted average exercise price (in dollars per share)	$ 8.31
Weighted average remaining contractual life	7 years 2 months 15 days
Stock options exercisable (in shares) | shares	1,540,548
Weighted average exercise price (in dollars per share)	$ 8.60