Stock Based Compensation - Summary of Stock Option Activity (Details) $ / shares in Units, $ in Thousands	9 Months Ended
	Sep. 30, 2018 USD ($) $ / shares shares
Number of Shares Underlying Outstanding Options
Outstanding at Beginning balance | shares	3,571,000
Options granted | shares	1,160,000
Options exercised | shares	(125,000)
Options cancelled | shares	(72,000)
Outstanding at Ending balance | shares	4,534,000
Exercisable at End of Period | shares	2,329,000
Weighted-Average Exercise Price
Outstanding at Beginning balance | $ / shares	$ 7.67
Options granted | $ / shares	8.13
Options exercised | $ / shares	1.97
Options cancelled | $ / shares	8.09
Outstanding at Ending balance | $ / shares	7.94
Exercisable at End of Period | $ / shares	$ 7.97
Weighted Average Remaining Contractual Term (Years)
Outstanding at Ending balance	7 years 9 months 14 days
Exercisable at End of Period	6 years 11 months 8 days
Outstanding | $	$ 3,001
Exercisable at End of Period | $	$ 1,946