Stock Awards - Summary of Stock Option Activity (Details) - Employee Stock Options - USD ($) $ / shares in Units, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Shares
Outstanding at beginning of period (in shares)	2,622,741
Granted (in shares)	1,059,372
Exercised (in shares)	(295,837)
Canceled (in shares)	(36,053)
Outstanding at end of period (in shares)	3,350,223	2,622,741
Weighted-Average Exercise Price
Outstanding at beginning of period (in dollars per share)	$ 11.67
Granted (in dollars per share)	38.47
Exercised (in dollars per share)	9.42
Canceled (in dollars per share)	19.57
Outstanding at end of period (in dollars per share)	$ 20.25	$ 11.67
Additional disclosures
Shares - Exercisable (in shares)	1,321,034
Shares - Vested and expected to vest (in shares)	3,350,223
Weighted-Average Exercise Price - Exercisable (in dollars per share)	$ 10.84
Weighted-Average Exercise Price - Vested and expected to vest (in dollars per share)	$ 20.25
Remaining Contractual Life - Outstanding	8 years 2 months 23 days	8 years 3 months 18 days
Remaining Contractual Life - Exercisable	7 years 6 months 18 days
Remaining Contractual Life - Vested and expected to vest	8 years 2 months 23 days
Aggregate Intrinsic Value - Outstanding	$ 165,553	$ 44,025
Aggregate Intrinsic Value - Exercisable	77,711
Aggregate Intrinsic Value - Vested and expected to vest	$ 165,553