Accounts Receivable Securitization - Narrative (Details) - USD ($)	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Accounts Receivable Securitization
Trade accounts receivable balance sold	$ 160,900,000	$ 118,200,000
Proceeds from collection of receivables	168,900,000	116,700,000
Sales of trade receivables	$ 48,600,000		$ 31,800,000
Average collection cycle for accounts receivable (in days) (less than)	60 days
Fair value of deferred purchase price notes	$ 39,900,000		$ 60,600,000
Non-cash investing activities related to increase in deferred purchase price	126,400,000	$ 92,100,000
Maximum
Accounts Receivable Securitization
Capacity of securitization program	$ 75,000,000