Accounts Receivable Securitization - Narrative (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Accounts Receivable Securitization
Trade accounts receivable balance sold	$ 223,400,000	$ 160,200,000	$ 384,300,000	$ 336,200,000
Proceeds from collection of receivables	185,900,000	$ 133,300,000	354,800,000	249,900,000
Sales of trade receivables	48,200,000		$ 48,200,000		$ 31,800,000
Average collection cycle for accounts receivable (in days) (less than)			60 days
Fair value of deferred purchase price notes	71,700,000		$ 71,700,000		$ 60,600,000
Non-cash investing activities related to increase in deferred purchase price			260,100,000	$ 203,900,000
Maximum
Accounts Receivable Securitization
Capacity of securitization program	$ 75,000,000		$ 75,000,000