Stock-Based Compensation - Schedule of Outstanding and Exercisable Options (Details) - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options outstanding, number of options (in shares)	4,352,391	4,299,810	4,105,369
Options outstanding, weighted average remaining contractual term	5 years 11 months 8 days	6 years 3 months 10 days	6 years 10 months 9 days
Options outstanding, weighted average exercise price (in dollars per share)	$ 4.61	$ 5.09	$ 4.76
Options exercisable, number of options (in shares)	3,238,512	3,115,466	2,664,203
Options exercisable, weighted average exercise price (in dollars per share)	$ 4.65	$ 4.07	$ 2.90
$0.79 - $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)	0.79
Options outstanding, exercise price range, upper range limit (in dollars per share)	$ 1.50
Options outstanding, number of options (in shares)	1,510,000
Options outstanding, weighted average remaining contractual term	3 years 1 month 13 days
Options outstanding, weighted average exercise price (in dollars per share)	$ 1.06
Options exercisable, number of options (in shares)	1,510,000
Options exercisable, 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]
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)	$ 5.50
Options outstanding, number of options (in shares)	992,457		50,000
Options outstanding, weighted average remaining contractual term	8 years 3 months 7 days		3 years 3 days
Options outstanding, weighted average exercise price (in dollars per share)	$ 3.23		$ 0.79
Options exercisable, number of options (in shares)	199,826		50,000
Options exercisable, weighted average exercise price (in dollars per share)	$ 2.76		$ 0.79
$5.51 - $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)	5.51
Options outstanding, exercise price range, upper range limit (in dollars per share)	$ 10.67
Options outstanding, number of options (in shares)	1,849,934		2,246,969
Options outstanding, weighted average remaining contractual term	6 years 11 months 26 days		8 years 4 months 6 days
Options outstanding, weighted average exercise price (in dollars per share)	$ 8.24		$ 7.82
Options exercisable, number of options (in shares)	1,528,686		805,803
Options exercisable, weighted average exercise price (in dollars per share)	$ 8.45		$ 7.15
$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
Options outstanding, weighted average remaining contractual term		2 years 3 days
Options outstanding, weighted average exercise price (in dollars per share)		$ 0.79
Options exercisable, number of options (in shares)		25,000
Options exercisable, weighted average exercise price (in dollars per share)		$ 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
Options outstanding, exercise price range, upper range limit (in dollars per share)		$ 1.50	$ 1.50
Options outstanding, number of options (in shares)		1,721,000	1,808,400
Options outstanding, weighted average remaining contractual term		4 years 1 month 20 days	5 years 1 month 9 days
Options outstanding, weighted average exercise price (in dollars per share)		$ 1.06	$ 1.07
Options exercisable, number of options (in shares)		1,721,000	1,808,400
Options exercisable, weighted average exercise price (in dollars per share)		$ 1.06	$ 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
Options outstanding, weighted average remaining contractual term		7 years 9 months 3 days
Options outstanding, weighted average exercise price (in dollars per share)		$ 7.85
Options exercisable, number of options (in shares)		1,369,466
Options exercisable, weighted average exercise price (in dollars per share)		$ 7.92