Benefit Plans - Benefit Plan Expenses (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 29, 2019	Jun. 30, 2018	Jun. 29, 2019	Jun. 30, 2018
Retirement Benefits [Abstract]
Service cost	$ 514	$ 533	$ 1,014	$ 1,066
Interest cost	813	501	1,597	1,002
Expected return on plan assets	(821)	(540)	(1,611)	(1,080)
Amortization of prior service	62	74	124	148
Net periodic benefit cost	$ 568	$ 568	$ 1,124	$ 1,136