Accounts Receivable Securitization - Narrative (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Accounts Receivable Securitization
Trade accounts receivable balance sold	$ 219,200,000	$ 211,300,000	$ 603,500,000	$ 547,500,000
Proceeds from collection of receivables	245,700,000	$ 179,700,000	600,500,000	429,600,000
Sales of trade receivables	51,400,000		$ 51,400,000		$ 31,800,000
Average collection cycle for accounts receivable (in days) (less than)			60 days
Fair value of deferred purchase price notes	45,400,000		$ 45,400,000		$ 60,600,000
Non-cash investing activities related to increase in deferred purchase price			404,700,000	$ 363,200,000
Maximum
Accounts Receivable Securitization
Capacity of securitization program	$ 75,000,000		$ 75,000,000