Stockholder's Equity (Deficit) - Summary of Number of Shares Authorized to be Issued and Available for Grant (Detail) - shares	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
2017 Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares authorized to be issued	2,945,443,000	997,785,000	600,900,000
Shares available for grant	848,241,000	137,908,000	131,113,000
2013 Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares authorized to be issued	2,047,269,000	2,058,619,000	2,154,600,000
Shares available for grant		1,550,000	79,946,000