Summary of Significant Accounting Policies - Life Insurance Policies (Details)	6 Months Ended
	Jun. 29, 2018 USD ($) Individual	Mar. 30, 2018 USD ($)	Dec. 31, 2017 USD ($)
Accounting Policies [Abstract]
Number of former employees covered under insurance policies | Individual	19
Average age of former employees covered under insurance policies	75 years
Borrowing against cash surrender value of life insurance policies	$ 22,700,000	$ 6,100,000
Gross cash surrender values of life insurance	31,300,000
Loans on cash surrender value	28,700,000		$ 0
Net cash surrender values of life insurance	2,577,000		31,547,000
Gross death benefit of life insurance contracts	42,000,000		$ 42,200,000
Life insurance proceeds to be received upon the death of participants	12,600,000
Life insurance gain to be recognized upon death of participants	$ 10,100,000