Stock Incentive Plans - Summary of Stock Option Activity Under 2006 and 2016 Plans, Including Grants to Non-employees (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Options Outstanding, Beginning balance	2,601,181	2,977,218
Options granted	292,688	465,271
Options exercised	(179,411)	(827,556)
Options forfeited	(18,545)	(13,752)
Options Outstanding, Ending balance	2,695,913	2,601,181	2,977,218
Options exercisable	1,579,689
Options vested and expected to vest	2,622,447
Options Outstanding, Weighted Average Exercise Price Per Share, Beginning Balance	$ 12.24	$ 6.16
Options Outstanding, Weighted Average Exercise Price Per Share, Options granted	64.59	36.76
Options Outstanding, Weighted Average Exercise Price Per Share, Options exercised	4.89	4.11
Options Outstanding, Weighted Average Exercise Price Per Share, Options forfeited	27.22	14.43
Options Outstanding, Weighted Average Exercise Price Per Share, Ending Balance	18.31	$ 12.24	$ 6.16
Options Outstanding, Weighted Average Exercise Price Per Share, Exercisable	7.80
Options Outstanding, Weighted Average Exercise Price Per Share, vested and expected to vest	$ 17.67
Options Outstanding, Weighted- Average Remaining Contractual Life (years)	7 years 3 months 10 days	7 years 2 months 1 day	6 years 11 months 4 days
Options exercisable, Weighted- Average Remaining Contractual Life (years)	6 years 3 months 14 days
Options vested and expected to vest, Weighted- Average Remaining Contractual Life (years)	7 years 2 months 23 days
Options Outstanding, Aggregate Intrinsic Value	$ 115,936	$ 113,958	$ 70,979
Options exercisable, Aggregate Intrinsic Value	83,901
Options vested and expected to vest, Aggregate Intrinsic Value	$ 114,380