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Revenue Recognition - Contract Balances (Details) - USD ($)
$ in Millions
9 Months Ended
Sep. 30, 2018
Jan. 01, 2018
Dec. 31, 2017
Contract with Customer, Asset and Liability [Abstract]      
Total contract liabilities $ 5.9   $ 5.7
Contract liabilities, revenue recognition period 36 months    
Capitalized Contract Cost [Abstract]      
Deferred sales commissions $ 7.2 $ 7.5  
Revenue, Practical Expedient [Abstract]      
Revenue, Practical Expedient, Initial Application and Transition, Nonrestatement of Modified Contract [true false] true    
Revenue, Remaining Performance Obligation, Optional Exemption, Performance Obligation [true false] true    
Revenue, Practical Expedient, Incremental Cost of Obtaining Contract [true false] true    
Minimum      
Capitalized Contract Cost [Abstract]      
Contract acquisition costs, amortization period 4 years    
Maximum      
Capitalized Contract Cost [Abstract]      
Contract acquisition costs, amortization period 5 years    
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2018-10-01 | Minimum      
Revenue, Practical Expedient [Abstract]      
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period 3 years    
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2018-10-01 | Maximum      
Revenue, Practical Expedient [Abstract]      
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period 5 years