Stock-Based Compensation (Details 2) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
$0.79 - $1.00
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options outstanding, exercise price range, lower range limit (in dollars per share)	$ 0.79	$ 0.79
Options outstanding, exercise price range, upper range limit (in dollars per share)	$ 1.00	$ 1.00
Options outstanding, number of options (in shares)	25,000	50,000
Options outstanding, weighted average remaining contractual term	2 years 4 days	3 years 4 days
Options outstanding, weighted average exercise price (in dollars per share)	$ 0.79	$ 0.79
Options exercisable, number of options (in shares)	25,000	50,000
Options exercisable, weighted average exercise price (in dollars per share)	$ 0.79	$ 0.79
1.01 - 1.50
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options outstanding, exercise price range, lower range limit (in dollars per share)	1.01	1.01	$ 1.01
Options outstanding, exercise price range, upper range limit (in dollars per share)	$ 1.50	$ 1.50	$ 1.50
Options outstanding, number of options (in shares)	1,721,000	1,808,400	1,862,400
Options outstanding, weighted average remaining contractual term	4 years 1 month 21 days	5 years 1 month 11 days	6 years 1 month 20 days
Options outstanding, weighted average exercise price (in dollars per share)	$ 1.06	$ 1.07	$ 1.07
Options exercisable, number of options (in shares)	1,721,000	1,808,400	1,851,400
Options exercisable, weighted average exercise price (in dollars per share)	$ 1.06	$ 1.07	$ 1.07
1.51 - 10.67
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options outstanding, exercise price range, lower range limit (in dollars per share)	1.51	1.51
Options outstanding, exercise price range, upper range limit (in dollars per share)	$ 10.67	$ 10.67
Options outstanding, number of options (in shares)	2,553,810	2,246,969
Options outstanding, weighted average remaining contractual term	7 years 9 months 4 days	8 years 3 months 35 days
Options outstanding, weighted average exercise price (in dollars per share)	$ 7.85	$ 7.82
Options exercisable, number of options (in shares)	1,369,466	805,803
Options exercisable, weighted average exercise price (in dollars per share)	$ 7.92	$ 7.15
$0.79 - $10.67
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options outstanding, exercise price range, lower range limit (in dollars per share)	0.79	0.79
Options outstanding, exercise price range, upper range limit (in dollars per share)	$ 10.67	$ 10.67
Options outstanding, number of options (in shares)	4,299,810	4,105,369
Options outstanding, weighted average remaining contractual term	6 years 3 months 11 days	6 years 8 months 70 days
Options outstanding, weighted average exercise price (in dollars per share)	$ 5.09	$ 4.76
Options exercisable, number of options (in shares)	3,115,466	2,664,203
Options exercisable, weighted average exercise price (in dollars per share)	$ 4.07	$ 2.90
$0.76 - $1.00
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options outstanding, exercise price range, lower range limit (in dollars per share)			0.76
Options outstanding, exercise price range, upper range limit (in dollars per share)			$ 1.00
Options outstanding, number of options (in shares)			50,000
Options outstanding, weighted average remaining contractual term			4 years 4 days
Options outstanding, weighted average exercise price (in dollars per share)			$ 0.79
Options exercisable, number of options (in shares)			50,000
Options exercisable, weighted average exercise price (in dollars per share)			$ 0.79
1.51 - 10.55
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options outstanding, exercise price range, lower range limit (in dollars per share)			1.51
Options outstanding, exercise price range, upper range limit (in dollars per share)			$ 10.55
Options outstanding, number of options (in shares)			1,680,334
Options outstanding, weighted average remaining contractual term			8 years 11 months 16 days
Options outstanding, weighted average exercise price (in dollars per share)			$ 8.10
Options exercisable, number of options (in shares)			289,997
Options exercisable, weighted average exercise price (in dollars per share)			$ 4.02
$0.79 - $10.67
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options outstanding, exercise price range, lower range limit (in dollars per share)			0.76
Options outstanding, exercise price range, upper range limit (in dollars per share)			$ 10.67
Options outstanding, number of options (in shares)			3,592,734
Options outstanding, weighted average remaining contractual term			7 years 5 months 5 days
Options outstanding, weighted average exercise price (in dollars per share)			$ 4.36
Options exercisable, number of options (in shares)			2,191,397
Options exercisable, weighted average exercise price (in dollars per share)			$ 1.45