Stock Options - Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Options
Outstanding, beginning of the period (in shares)	2,071,616
Granted (in shares)	355,056
Exercised (in shares)	(206,404)
Forfeited (in shares)	(24,935)
Outstanding at ending of the year (in shares)	2,195,333	2,071,616
Exercisable (in shares)	1,272,700
Weighted Average Exercise Price
Outstanding, beginning of the period (in dollars per share)	$ 1.47
Granted (in dollars per share)	12.40
Exercised (in dollars per share)	1.80
Forfeited (in dollars per share)	1.03
Outstanding, end of the period (in dollars per share)	3.20	$ 1.47
Exercisable (in dollars per share)	$ 1.61
Weighted average remaining contractual term
Outstanding (in years)	7 years	5 years 10 months 24 days
Exercisable (in years)	5 years 6 months
Aggregate intrinsic value
Outstanding	$ 71,342
Exercisable	$ 43,342