Pension and Post-Retirement Benefit Plans - Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 27, 2020	Jun. 29, 2019	Jun. 27, 2020	Jun. 29, 2019
Retirement Benefits [Abstract]
Service cost	$ 198	$ 874	$ 550	$ 1,230
Interest cost	451	662	816	1,033
Expected return on plan assets	(555)	(1,193)	(1,224)	(1,797)
Amortization of actuarial loss	505	409	918	827
Total net periodic benefit cost	$ 599	$ 752	$ 1,060	$ 1,293