Stockholders' Equity - Summary of Common Stock Reserved for Future Issuance (Detail)	Dec. 31, 2017 shares
Class Of Stock [Line Items]
Common stock reserved for future issuance	134,877,000
2013 Equity incentive plan
Class Of Stock [Line Items]
Outstanding options and restricted stock unit awards	9,567,000
Available for future grants	10,390,944
2013 Employee stock purchase plan
Class Of Stock [Line Items]
Common stock reserved for future issuance	2,720,000
Available for future grants	2,719,701
Class B common stock
Class Of Stock [Line Items]
Common stock reserved for future issuance	12,199,000
Preferred Stock
Class Of Stock [Line Items]
Common stock reserved for future issuance	100,000,000