Stock-Based Compensation (Details 2)	3 Months Ended
	Mar. 31, 2018 $ / shares shares
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Stock options outstanding (in shares) | shares	4,795,605
Weighted average exercise price (in dollars per share)	$ 4.84
Weighted average remaining contractual life	6 years 5 months 16 days
Stock options exercisable (in shares) | shares	3,553,271
Weighted average exercise price (in dollars per share)	$ 4.63
$0.79 - $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	1,746,000
Weighted average exercise price (in dollars per share)	$ 1.06
Weighted average remaining contractual life	3 years 10 months 10 days
Stock options exercisable (in shares) | shares	1,746,000
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	797,169
Weighted average exercise price (in dollars per share)	$ 3.19
Weighted average remaining contractual life	8 years 7 months 13 days
Stock options exercisable (in shares) | shares	205,666
Weighted average exercise price (in dollars per share)	$ 2.77
$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	2,252,436
Weighted average exercise price (in dollars per share)	$ 8.35
Weighted average remaining contractual life	7 years 8 months 16 days
Stock options exercisable (in shares) | shares	1,601,605
Weighted average exercise price (in dollars per share)	$ 8.76