Accumulated Other Comprehensive Earnings Reconciliation of Changes in Accumulated Other Comprehensive Earnings (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 30, 2013	Mar. 31, 2012
Reconciliation of Changes in Accumulated Other Comprehensive Earnings [Line Items]
Unrealized gain on AFS securities	$ 33,695	$ 20,766
Net realized gain on AFS securities reclassified to investment income, net	(1,632)	(146)
Amortization of actuarial losses reclassifed to operating and administrative expenses	806	478
AFS Securities
Reconciliation of Changes in Accumulated Other Comprehensive Earnings [Line Items]
Beginning balance	58,286	44,703
Unrealized gain on AFS securities	33,695	20,766
Net realized gain on AFS securities reclassified to investment income, net	(1,632)	(146)
Net other comprehensive earnings	32,063	20,620
Ending balance	90,349	65,323
Postretirement Benefits
Reconciliation of Changes in Accumulated Other Comprehensive Earnings [Line Items]
Beginning balance	(19,997)	(14,442)
Amortization of actuarial losses reclassifed to operating and administrative expenses	806	478
Net other comprehensive earnings	806	478
Ending balance	(19,191)	(13,964)
Accumulated Other Comprehensive Earnings
Reconciliation of Changes in Accumulated Other Comprehensive Earnings [Line Items]
Beginning balance	38,289	30,261
Unrealized gain on AFS securities	33,695	20,766
Net realized gain on AFS securities reclassified to investment income, net	(1,632)	(146)
Amortization of actuarial losses reclassifed to operating and administrative expenses	806	478
Net other comprehensive earnings	32,869	21,098
Ending balance	$ 71,158	$ 51,359