Pension Plan Pension plan net periodic benefit costs (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jul. 03, 2015	Jun. 27, 2014	Jul. 03, 2015	Jun. 27, 2014
Qualified Pension Plan [Member]
Defined Benefit Plan Disclosure
Service cost for benefits earned during the year	$ 3,532	$ 2,940	$ 7,065	$ 5,880
Interest cost on projected benefit obligation	6,879	7,208	13,757	14,417
Expected return on plan assets	(11,033)	(10,261)	(22,065)	(20,523)
Amortization of prior service cost (credit)	15	20	29	45
Recognized net loss	2,479	1,038	4,959	2,057
Net pension benefit cost	1,872	945	3,745	1,876
Supplemental Employee Retirement Plans [Member]
Defined Benefit Plan Disclosure
Service cost for benefits earned during the year	51	64	103	128
Interest cost on projected benefit obligation	80	86	159	171
Expected return on plan assets	0	0	0	0
Amortization of prior service cost (credit)	0	0	0	0
Recognized net loss	55	23	110	45
Net pension benefit cost	$ 186	$ 173	$ 372	$ 344