Debt (Other Credit Facilities) (Narrative) (Details) $ in Millions	Dec. 31, 2019 USD ($)	Dec. 31, 2019 CAD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2018 CAD ($)
Debt Instrument [Line Items]
Letters of credit issued	$ 115,100,000		$ 128,400,000
Other Credit Facilities [Member]
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity		$ 20.0		$ 20.0
Other Credit Facilities [Member] | Canadian Dollars [Member]
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity	15,400,000		14,700,000
Long-term debt obligations	0		0
Line of Credit [Member] | Standby Letters of Credit [Member]
Debt Instrument [Line Items]
Letters of credit issued	17,100,000		$ 40,200,000
Line of Credit [Member] | Letter of Credit [Member]
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity	$ 50,000,000.0
Line of Credit [Member] | Letter of Credit [Member] | Standby Letters of Credit [Member]
Debt Instrument [Line Items]
Line of credit facility, interest rate (percentage)	0.40%	0.40%	0.75%	0.75%