Stock-Based Awards - Summary of Activity Under Restricted Stock Units (RSUs) from 2014 Plan (Details) - Restricted Stock Units - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
RSUs Outstanding, Number of Shares, Unvested, Beginning Balance	573,744	197,151	31,000
Number of Shares, RSUs granted	516,161	477,816	187,260
Number of Shares, RSUs released	(156,021)	(52,273)	(18,209)
Number of Shares, RSUs cancelled	(112,324)	(48,950)	(2,900)
RSUs Outstanding, Number of Shares, Unvested, Ending Balance	821,560	573,744	197,151
RSUs Outstanding, Weighted-Average Grant Date Fair Value, Unvested, Beginning Balance	$ 71.45	$ 87.24	$ 53.23
Weighted-Average Grant Date Fair Value, RSUs granted	71.58	66.83	89.67
Weighted-Average Grant Date Fair Value, RSUs released	71.93	82.59	54.72
Weighted-Average Grant Date Fair Value, RSUs cancelled	76.78	78.04	84.89
RSUs Outstanding, Weighted-Average Grant Date Fair Value, Unvested, Ending Balance	$ 70.71	$ 71.45	$ 87.24