Defined Benefit Plans (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 28, 2018	Mar. 29, 2017	Dec. 27, 2017
Components of net periodic benefit cost [Abstract]
Interest cost	$ 19	$ 21
Amortization of net loss	28	23
Net periodic benefit cost	47	44
Employer contributions	100	$ 100
Estimated employer contributions remainder of current fiscal year	100
Additional minimum pension liability	$ 1,000		$ 982