Employee Benefits (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jul. 04, 2015 USD ($) plan	Jun. 28, 2014 USD ($)	Jul. 04, 2015 USD ($) plan	Jun. 28, 2014 USD ($)
Components of net periodic benefit cost:
Service cost	$ 2,495	$ 2,004	$ 4,942	$ 3,860
Interest cost	2,587	2,418	5,137	4,821
Expected return on plan assets	(2,173)	(2,179)	(4,288)	(4,364)
Amortization and other	1,377	581	2,126	1,051
Net periodic benefit cost	$ 4,286	$ 2,824	$ 7,917	$ 5,368
Defined benefit pension plan
Target allocation and pension plan asset allocation
Number of defined benefit plans | plan	2		2
Contributions expected to be made to defined benefit pension plans			$ 0