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Deferred Commissions (Details) - USD ($)
3 Months Ended
Mar. 31, 2019
Mar. 31, 2018
Dec. 31, 2018
Capitalized Contract Cost [Line Items]      
Deferred commissions $ 23,600,000   $ 21,900,000
Deferred commissions amortization 3,800,000 $ 3,500,000  
Deferred commissions impairment $ 0 $ 0  
Minimum      
Capitalized Contract Cost [Line Items]      
Sales commissions amortization period 3 years    
Maximum      
Capitalized Contract Cost [Line Items]      
Sales commissions amortization period 7 years