Stock-Based Awards - Summary of Activity Under Stock Option Plans Including 2011 Plan and 2014 Plan (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of Options, Outstanding, Beginning Balance	4,429,472	3,826,963	2,739,475
Number of Options, Options granted	1,328,860	1,435,995	2,013,350
Number of Options, Options assumed	639,897
Number of Options, Options exercised	(478,470)	(425,922)	(795,825)
Number of Options, Options cancelled	(520,349)	(407,564)	(130,037)
Number of Options, Outstanding, Ending Balance	5,399,410	4,429,472	3,826,963	2,739,475
Number of Options, Vested and exercisable — December 31, 2017	2,709,510
Number of Options, Vested and expected to vest — December 31, 2017	5,216,110
Weighted Average Exercise Price, Outstanding, Beginning Balance	$ 61.85	$ 56.36	$ 16.15
Weighted Average Exercise Price, Options granted	71.99	67.00	90.60
Weighted Average Exercise Price, Options assumed	27.97
Weighted Average Exercise Price, Options exercised	16.25	21.21	8.65
Weighted Average Exercise Price, Options cancelled	78.70	70.87	31.49
Weighted Average Exercise Price, Outstanding, Ending Balance	62.75	$ 61.85	$ 56.36	$ 16.15
Weighted Average Exercise Price, Vested and exercisable — December 31, 2017	53.53
Weighted Average Exercise Price, Vested and expected to vest — December 31, 2017	$ 62.50
Weighted Average Remaining Contractual Term (Years), Outstanding	7 years 4 months 24 days	8 years 2 months 19 days	8 years 6 months 29 days	8 years 5 months 4 days
Weighted Average Remaining Contractual Term (Years), Vested and exercisable — December 31, 2017	6 years 2 months 19 days
Weighted Average Remaining Contractual Term (Years), Vested and expected to vest — December 31, 2017	7 years 4 months 6 days
Aggregate Intrinsic Value, Outstanding	$ 37,687	$ 79,135	$ 217,386	$ 79,840
Aggregate Intrinsic Value, Vested and exercisable — December 31, 2017	34,558
Aggregate Intrinsic Value, Vested and expected to vest — December 31, 2017	$ 37,528