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Description of the Business and Summary of Significant Accounting Policies - Deferred Commissions, Net (Details) - USD ($)
 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Capitalized Contract Cost [Line Items]      
Additional contract costs deferred $ 32,000,000 $ 19,400,000  
Deferred contract costs, amortization period 5 years    
Amortization of deferred commissions $ 12,100,000 6,600,000 $ 3,700,000
Impairment loss related to deferred costs 0 0 $ 0
Prepaid Expenses and Other Current Assets | Deferred Commissions      
Capitalized Contract Cost [Line Items]      
Deferred contract costs 14,500,000 8,100,000  
Other Assets | Deferred Commissions      
Capitalized Contract Cost [Line Items]      
Deferred contract costs $ 38,300,000 $ 24,800,000