Debt (Schedule of Letters of Credit Facilities) (Details) - USD ($)	Mar. 31, 2019	Dec. 31, 2018
Letter of Credit [Member]
Debt Instrument [Line Items]
Letters of credit, Limit	$ 206,900,000
Letters of credit, Used	49,600,000
Letters of credit, Available	157,300,000
Letter of Credit [Member] | Bi-lateral Facility [Member]
Debt Instrument [Line Items]
Letters of credit, Limit	25,000,000	$ 25,000,000
Letters of credit, Used	13,400,000
Letters of credit, Available	11,600,000
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Letter of credit maximum sublimit	150,000,000	150,000,000
Letters of credit, Limit	200,000,000	$ 200,000,000
Revolving Credit Facility [Member] | Letter of Credit [Member]
Debt Instrument [Line Items]
Letters of credit, Available	150,000,000
Accounts Receivable Securitization Facility [Member]
Debt Instrument [Line Items]
Letters of credit, Used	36,200,000
Accounts Receivable Securitization Facility [Member] | Letter of Credit [Member]
Debt Instrument [Line Items]
Letters of credit, Limit	31,900,000
Letters of credit, Used	36,200,000
Letters of credit, Available	$ (4,300,000)