Debt (Other Credit Facilities) (Narrative) (Details) - USD ($)	Jun. 30, 2021	Dec. 31, 2020
Debt Instrument [Line Items]
Letters of credit issued	$ 123,700,000	$ 151,800,000
Other Credit Facilities
Debt Instrument [Line Items]
Long-term debt obligations	0	0
Line of Credit | Letters of Credit
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity	50,000,000.0
Standby Letters of Credit | Line of Credit
Debt Instrument [Line Items]
Letters of credit issued	$ 26,200,000	$ 18,200,000
Standby Letters of Credit | Line of Credit | Letters of Credit
Debt Instrument [Line Items]
Line of credit facility, interest rate (percentage)	0.40%	0.50%