Employee Benefit Plans Employe Benefit Plans (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 27, 2017	Dec. 28, 2016	Dec. 30, 2015
Defined Benefit Plan Disclosure [Line Items]
Settlement loss recognized	$ (21)	$ (24,297)
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Employer contributions	0	9,546
Assets used for settlements	0	67,728
Settlement loss recognized	$ 0	$ (24,297)	$ 0