Pension and Other Postretirement Benefits - Other Postretirement Benefits (Details) - Other Postretirement Benefit Plan - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jul. 01, 2018	Jun. 30, 2019	Jul. 01, 2018
Pension Benefits
Service cost	$ 7	$ 5	$ 14	$ 10
Interest cost	400	369	800	738
Amortization of actuarial loss	844	1,184	1,688	2,368
Amortization of prior service credit	(1,191)	(1,643)	(2,382)	(3,182)
Net periodic postretirement benefit income	$ 60	$ (85)	$ 120	$ (66)