Debt (Other Credit Facilities) (Narrative) (Details) - USD ($)	Mar. 31, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Line of credit facility, letters of credit issued	$ 130,700,000	$ 128,400,000
Foreign Line of Credit [Member] | Canadian Dollars [Member]
Debt Instrument [Line Items]
Long-term debt obligations	0	0
Line of Credit [Member]
Debt Instrument [Line Items]
Line of credit facility, letters of credit issued	40,200,000	$ 40,200,000
Line of Credit [Member] | Letters of Credit [Member]
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity	$ 50,000,000
Line of Credit [Member] | Letters of Credit [Member] | Performance Standby [Member]
Debt Instrument [Line Items]
Line of credit facility, interest rate (percentage)	0.50%	0.75%