Restricted Investments (Details)		9 Months Ended
	Oct. 01, 2020	Sep. 30, 2019 USD ($)	Dec. 31, 2018 USD ($)
Restricted Investments
Guaranteed interest rate on deposit (as a percent)		0.05
Restricted investments		$ 563,983,000	$ 653,158,000
Restricted investments, long-term		$ 513,193,000	$ 503,158,000
Forecast
Restricted Investments
Guaranteed interest rate on deposit (as a percent)	0.04