Net Periodic Benefit Expense - Defined Benefit Pension Plans (Details) - Pension plans, defined benefit [Member] - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Apr. 01, 2017
Defined Benefit Plan Disclosure [Line Items]
Service costs--increase in benefit obligation earned	$ 100	$ 133
Interest cost on projected benefit obligation	180	263
Expected return on plan assets	(58)	(169)
Amortization of net actuarial loss	182	237
Amortization of prior service cost	16	16
Net pension expense of defined benefit pension plans	$ 420	$ 480