XML 99 R68.htm IDEA: XBRL DOCUMENT v3.10.0.1
Debt - Schedule of Debt Obligations (Detail) - USD ($)
$ in Millions
Sep. 30, 2018
Dec. 31, 2017
Dec. 31, 2016
Debt Instrument [Line Items]      
Total debt $ 680.0 $ 1,132.3 $ 1,158.2
Less unamortized discount on Term Debt 1.7 0.9 1.1
Less unamortized debt issuance costs on Senior Notes and Term Debt 6.5 11.6 15.0
Less current portion of long-term debt 6.8   2.3
Long-term debt, less current portion 665.0 1,119.8 1,139.8
Term Debt [Member]      
Debt Instrument [Line Items]      
Total debt $ 680.0 657.3 683.2
Senior Notes [Member]      
Debt Instrument [Line Items]      
Total debt   $ 475.0 $ 475.0