Long-term Debt - Schedule of Long-term Debt (Details) - USD ($)	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Debt Instrument [Line Items]
Obligations under finance leases	$ 93,900,000		$ 86,500,000
Total long-term debt	352,900,000		344,500,000
Amortization of debt issuance costs	300,000	$ 200,000
Revolving credit facility
Debt Instrument [Line Items]
Amounts borrowed (Credit Facility)	259,000,000.0		258,000,000.0
Total long-term debt	259,000,000.0		258,000,000.0
Outstanding letters of credit	43,600,000		19,500,000
Amounts available to borrow	406,900,000		402,400,000
Unamortized debt issuance costs	3,400,000		$ 900,000
Revolving credit facility, expansion feature	200,000,000.0
Average borrowings	202,500,000	336,400,000
Unused Credit Facility and letter of credit participation fees	400,000	300,000
Amortization of debt issuance costs	$ 300,000	$ 200,000
Weighted-average interest rate	1.40%	2.70%
Minimum | Revolving credit facility
Debt Instrument [Line Items]
Average borrowings	$ 142,500,000	$ 151,500,000
Maximum | Revolving credit facility
Debt Instrument [Line Items]
Average borrowings	$ 301,000,000.0	$ 499,300,000