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Adoption of ASC 606 - Additional Information (Detail) - USD ($)
$ in Millions
 3 Months Ended 9 Months Ended
Sep. 30, 2018
Sep. 30, 2018
Jun. 30, 2018
Dec. 31, 2017
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]        
Revenue, remaining performance obligation, expected timing of satisfaction, description   contracts have an original expected duration of one year or less, for our contracts with a duration greater than one year, the average remaining expected duration was approximately 14 months    
Average revenue remaining performance obligation expected timing of satisfaction period   14 months    
Contract liabilities $ 5.6 $ 5.6 $ 6.1 $ 7.0
Contract with customer, liability partially offset revenue recognized $ 0.8 $ 4.1    
Difference between Revenue Guidance in Effect before and after Topic 606 [Member]        
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]        
Revenue used to determine transaction price, period 1 month 1 month