Accounts Receivable Securitization - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Accounts Receivable Securitization
Trade accounts receivable balance sold	$ 695,200,000	$ 600,300,000
Proceeds from collection of receivables	645,500,000	627,200,000
Sales of trade receivables	31,800,000	19,500,000
Fair value of deferred purchase price notes	$ 60,600,000	$ 30,600,000
Average collection cycle for accounts receivable (in days) (less than)	60 days
Period for which the entity will be able to comply with the financial covenants	12 months
Maximum
Accounts Receivable Securitization
Capacity of securitization program	$ 75,000,000