Contract Balances - Additional Information (Detail1) $ in Millions	9 Months Ended
	Sep. 30, 2018 USD ($)
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2018-10-01
Contract With Customer Asset And Liability [Line Items]
Revenue, Remaining performance obligation	$ 151.0
Revenue, Remaining performance obligations, Expected timing of satisfaction, Period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2019-10-01
Contract With Customer Asset And Liability [Line Items]
Revenue, Remaining performance obligation	$ 4.9
Revenue, Remaining performance obligations, Thereafter	thereafter
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: (nil)
Contract With Customer Asset And Liability [Line Items]
Revenue, Remaining performance obligation	$ 156.0
Revenue, Remaining performance obligations, Expected timing of satisfaction, Period