Marketable Securities (Details) - USD ($)	3 Months Ended
	Apr. 01, 2018	Dec. 31, 2017
Line of Credit Facility [Line Items]
Letters of credit		$ 56,000,000
Letters of credit, outstanding	$ 0
Letter of Credit
Line of Credit Facility [Line Items]
Collateral, letters of credit	$ 63,000,000	$ 63,100,000
Short-term Marketable Securities | Minimum
Line of Credit Facility [Line Items]
Marketable securities, remaining maturities (in months)	1 month
Short-term Marketable Securities | Maximum
Line of Credit Facility [Line Items]
Marketable securities, remaining maturities (in months)	12 months
Long-term Marketable Securities | Minimum
Line of Credit Facility [Line Items]
Marketable securities, remaining maturities (in months)	13 months
Long-term Marketable Securities | Maximum
Line of Credit Facility [Line Items]
Marketable securities, remaining maturities (in months)	35 months