Restricted Cash and Investments (Details) $ in Thousands	Oct. 01, 2021	Oct. 01, 2020	Sep. 30, 2021 USD ($)	Dec. 31, 2020 USD ($)
Restricted Cash and Cash Equivalents Items [Line Items]
Guaranteed interest rate on deposit (as a percent)		0.04
Restricted investments			$ 319,980	$ 487,587
Restricted investments, long-term			$ 73,400	$ 306,601
Subsequent Event
Restricted Cash and Cash Equivalents Items [Line Items]
Guaranteed interest rate on deposit (as a percent)	0.0009