Stockholders’ Equity - Summary of Stock Option Activity (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Number of shares
Outstanding, beginning of period (in shares)	5,369
Options granted (in shares)	347
Options exercised (in shares)	(76)
Options canceled (in shares)	(10)
Outstanding, end of period (in shares)	5,630	5,369
Weighted average exercise price
Outstanding, beginning of period (in dollars per share)	$ 1.09
Options granted (in dollars per share)	9.70
Options exercised (in dollars per share)	0.81
Options canceled (in dollars per share)	1.66
Outstanding, end of period (in dollars per share)	$ 1.62	$ 1.09
Outstanding, Weighted average remaining contractual term (years)	7 years 4 months 24 days	7 years 4 months 24 days
Outstanding, Aggregate intrinsic value	$ 47,168	$ 29,863
Options exercisable at end of period
Number of shares	2,439
Weighted average exercise price (in dollars per share)	$ 0.85
Weighted average remaining contractual term (years)	6 years 9 months 18 days
Aggregate intrinsic value	$ 22,469
Options vested as of end of period and expected to vest after end of period
Number of shares	4,518
Weighted average exercise price (in dollars per share)	$ 1.63
Weighted average remaining contractual term (years)	8 years
Aggregate intrinsic value	$ 43,536