Retirement Plans - Other Postretirement Benefit Plan (Details) - Other post-retirement benefit plan - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 28, 2015	Jun. 30, 2016	Jun. 28, 2015
Defined Benefit Plan Disclosure
Service cost	$ 1	$ 1	$ 2	$ 2
Interest cost	52	51	104	102
Amortization of gain	(37)	(25)	(75)	(50)
(Income) expense, net	$ 16	$ 27	$ 31	$ 54