XML 79 R63.htm IDEA: XBRL DOCUMENT v3.8.0.1
External Debt and Financing Arrangements - Components of External Long-Term Debt (Detail) - USD ($)
Dec. 31, 2017
Dec. 31, 2016
Debt Instrument [Line Items]    
Long-term debt $ 1,507,600,000 $ 1,431,100,000
Less: current portion 0 0
Total long-term debt 1,507,600,000 1,431,100,000
Senior Unsecured Notes [Member] | Notes Due June Twenty Twenty [Member]    
Debt Instrument [Line Items]    
Long-term debt 398,300,000 397,600,000
Senior Unsecured Notes [Member] | Notes Due June Twenty Twenty Five [Member]    
Debt Instrument [Line Items]    
Long-term debt 494,300,000 493,500,000
Revolving Credit Facility [Member]    
Debt Instrument [Line Items]    
Long-term debt 615,000,000 540,000,000
Less: current portion $ 0 $ 0