Pension Plan Pension plan net periodic benefit costs (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 27, 2014	Jun. 28, 2013	Jun. 27, 2014	Jun. 28, 2013
Qualified Pension Plan [Member]
Defined Benefit Plan Disclosure
Service cost for benefits earned during the year	$ 2,940	$ 3,587	$ 5,880	$ 7,174
Interest cost on projected benefit obligation	7,208	6,399	14,417	12,798
Expected return on plan assets	(10,261)	(10,337)	(20,523)	(20,674)
Amortization of prior service cost (credit)	20	25	45	50
Recognized net loss	1,038	2,304	2,057	4,581
Net pension benefit cost	945	1,978	1,876	3,929
Supplemental Employee Retirement Plans [Member]
Defined Benefit Plan Disclosure
Service cost for benefits earned during the year	64	85	128	170
Interest cost on projected benefit obligation	86	83	171	155
Expected return on plan assets	0	0	0	0
Amortization of prior service cost (credit)	0	0	0	0
Recognized net loss	23	53	45	130
Defined Benefit Plan, Recognized Net Gain (Loss) Due to Settlements and Curtailments	0	277	0	277
Net pension benefit cost	173	498	344	732
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