Stock-Based Compensation (Details 2)	6 Months Ended
	Jun. 30, 2018 $ / shares shares
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Stock options outstanding (in shares) | shares	4,768,105
Weighted average exercise price (in dollars per share)	$ 4.76
Weighted average remaining contractual life	6 years 3 months 1 day
Stock options exercisable (in shares) | shares	3,546,700
Weighted average exercise price (in dollars per share)	$ 4.63
$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)	0.55
Range of exercise prices (in dollars per share)	$ 1.50
Stock options outstanding (in shares) | shares	1,735,000
Weighted average exercise price (in dollars per share)	$ 1.06
Weighted average remaining contractual life	3 years 7 months 10 days
Stock options exercisable (in shares) | shares	1,735,000
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	873,469
Weighted average exercise price (in dollars per share)	$ 3.18
Weighted average remaining contractual life	8 years 6 months 8 days
Stock options exercisable (in shares) | shares	202,166
Weighted average exercise price (in dollars per share)	$ 2.75
$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	2,159,636
Weighted average exercise price (in dollars per share)	$ 8.38
Weighted average remaining contractual life	7 years 5 months 13 days
Stock options exercisable (in shares) | shares	1,609,534
Weighted average exercise price (in dollars per share)	$ 8.72