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Summary of Significant Accounting Policies (Details)
 12 Months Ended
Dec. 31, 2018
USD ($)
segment
Dec. 31, 2017
USD ($)
Dec. 31, 2016
USD ($)
Accounting Policies [Abstract]      
Impairments to investments $ 0 $ 0 $ 0
Property, Plant and Equipment [Line Items]      
Fully depreciated assets taken out of service 3,500,000 4,800,000  
Property and equipment asset impairments 0 0 0
Goodwill impairments 0 0 0
Indefinite-lived intangible asset impairments 0 0 0
Finite-lived intangible asset impairments $ 0 0 0
Deferred sales commission asset estimated period of benefit 6 years    
Deferred sales commission amortization expense $ 2,967,000 8,025,000 11,980,000
Deferred sales commission asset impairments 0 0 0
Deferred sales commissions expensed as incurred $ 4,700,000 1,400,000 3,100,000
Termination period 60 days    
Expensed advertising costs $ 5,200,000 $ 1,500,000 $ 2,700,000
Number of operating segments | segment 1    
Number of reporting units | segment 1    
Minimum      
Property, Plant and Equipment [Line Items]      
Estimated useful life 1 year    
Termination period 3 months    
Maximum      
Property, Plant and Equipment [Line Items]      
Estimated useful life 15 years    
Termination period 12 months    
Software and Software Development Costs      
Property, Plant and Equipment [Line Items]      
Estimated useful life 4 years