Pension Plan Pension plan net periodic benefit costs (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 26, 2014	Sep. 27, 2013	Sep. 26, 2014	Sep. 27, 2013
Qualified Pension Plan [Member]
Defined Benefit Plan Disclosure
Service cost for benefits earned during the year	$ 2,940	$ 3,587	$ 8,820	$ 10,761
Interest cost on projected benefit obligation	7,208	6,399	21,625	19,197
Expected return on plan assets	(10,262)	(10,337)	(30,785)	(31,011)
Amortization of prior service cost (credit)	23	25	68	75
Recognized net loss	1,028	2,387	3,085	6,968
Net pension benefit cost	937	2,061	2,813	5,990
Supplemental Employee Retirement Plans [Member]
Defined Benefit Plan Disclosure
Service cost for benefits earned during the year	64	85	192	255
Interest cost on projected benefit obligation	85	78	256	233
Expected return on plan assets	0	0	0	0
Amortization of prior service cost (credit)	0	0	0	0
Recognized net loss	23	65	68	195
Defined Benefit Plan, Recognized Net Gain (Loss) Due to Settlements and Curtailments	0	0	0	277
Net pension benefit cost	172	228	516	960
Pension Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure
Defined Benefit Plan, Recognized Net Gain (Loss) Due to Settlements and Curtailments	$ 0	$ 0	$ 0	$ 0