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Summary of Significant Accounting Policies - Additional Information (Details)
shares in Thousands
 12 Months Ended
Dec. 31, 2020
USD ($)
reportingUnit
segment
shares
Dec. 31, 2019
USD ($)
shares
Dec. 31, 2018
USD ($)
shares
Finite-Lived Intangible Assets [Line Items]      
Number of operating segments | segment 1    
Number of reportable segments | segment 1    
Restricted cash included in other assets $ 436,000 $ 434,000 $ 430,000
Allowance for credit losses for available-for-sale investment securities 0    
Impairment losses for goodwill 0 0 0
Impairment charges related to the identified long-lived assets 0 0 0
Deferred revenue recognized during the period $ 4,500,000 3,400,000  
Amortization period of deferred cost 3 years    
Deferred costs $ 10,300,000 9,500,000  
Deferred costs, current 5,500,000 4,800,000  
Deferred costs, noncurrent 4,800,000 4,600,000  
Amortization expense 5,800,000 4,200,000 2,000,000.0
Advertising expense $ 7,000,000.0 $ 5,800,000 $ 4,500,000
Minimum      
Finite-Lived Intangible Assets [Line Items]      
Subscription agreement term 1 month    
Maximum      
Finite-Lived Intangible Assets [Line Items]      
Subscription agreement term 1 year    
Unvested restricted stock units      
Finite-Lived Intangible Assets [Line Items]      
Vesting period 4 years    
Performance shares      
Finite-Lived Intangible Assets [Line Items]      
Shares excluded from net loss per share attributable to common stockholders (in shares) | shares 79 187 358
Capitalized software development costs      
Finite-Lived Intangible Assets [Line Items]      
Estimated useful lives (in years) 3 years    
Goodwill      
Finite-Lived Intangible Assets [Line Items]      
Number of reporting units | reportingUnit 1