Debt - Other Credit Facilities - Narrative (Details) - USD ($)	Sep. 30, 2021	Dec. 31, 2020
Debt Instrument [Line Items]
Letters of credit issued	$ 134,900,000	$ 151,800,000
Other Credit Facilities
Debt Instrument [Line Items]
Long-term debt obligations	$ 4,000,000	0
Weighted average interest rate (percentage)	3.20%
Line of Credit | Letters of Credit
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity	$ 50,000,000
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%