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Income Taxes - Summary of Reconciliation of Statutory Federal Income Tax Rate (Details)
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Effective Income Tax Rate Continuing Operations Tax Rate Reconciliation [Abstract]      
Tax benefit (expense) computed at the federal statutory rate 21.00% 21.00% 21.00%
State tax benefit (expense), net of federal benefit 8.30% 7.60% 5.10%
Change in valuation allowance (58.90%) (38.50%) (28.40%)
Differences between U.S. and foreign tax rates on foreign income (1.40%) (1.00%) (0.90%)
Stock-based compensation benefit (expense) 17.80% 0.80% (1.20%)
U.S. federal research & development credit benefit 8.40% 6.30% 5.20%
U.K. corporate rate increase 4.30%    
Acquisitions and divestitures (0.10%) 3.40% 0.20%
Other benefits (expenses) (1.40%) 0.40% (1.20%)
Total income tax benefit (expense) (2.00%) 0.00% (0.20%)