Benefit Plans - Benefit Plan Expenses (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 30, 2019	Mar. 31, 2018
Retirement Benefits [Abstract]
Service cost	$ 500	$ 533
Interest cost	784	501
Expected return on plan assets	(790)	(540)
Amortization of prior service	62	74
Net periodic benefit cost	$ 556	$ 568