Accumulated Other Comprehensive Earnings Reconciliation of Changes in Accumulated Other Comprehensive Earnings (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 29, 2013	Jun. 30, 2012	Jun. 29, 2013	Jun. 30, 2012
Reconciliation of Changes in Accumulated Other Comprehensive Earnings [Line Items]
Unrealized loss on AFS securities	$ (34,450)	$ (12,519)	$ (755)	$ 8,247
Net realized gain on AFS securities reclassified to investment income, net	(4,044)	(2,555)	(5,676)	(2,701)
Amortization of actuarial losses reclassifed to operating and administrative expenses	806	478	1,612	956
AFS Securities
Reconciliation of Changes in Accumulated Other Comprehensive Earnings [Line Items]
Beginning balance	90,349	65,323	58,286	44,703
Unrealized loss on AFS securities	(34,450)	(12,519)	(755)	8,247
Net realized gain on AFS securities reclassified to investment income, net	(4,044)	(2,555)	(5,676)	(2,701)
Net other comprehensive (losses) earnings	(38,494)	(15,074)	(6,431)	5,546
Ending balance	51,855	50,249	51,855	50,249
Postretirement Benefits
Reconciliation of Changes in Accumulated Other Comprehensive Earnings [Line Items]
Beginning balance	(19,191)	(13,964)	(19,997)	(14,442)
Amortization of actuarial losses reclassifed to operating and administrative expenses	806	478	1,612	956
Net other comprehensive (losses) earnings	806	478	1,612	956
Ending balance	(18,385)	(13,486)	(18,385)	(13,486)
Accumulated Other Comprehensive Earnings
Reconciliation of Changes in Accumulated Other Comprehensive Earnings [Line Items]
Beginning balance	71,158	51,359	38,289	30,261
Unrealized loss on AFS securities	(34,450)	(12,519)	(755)	8,247
Net realized gain on AFS securities reclassified to investment income, net	(4,044)	(2,555)	(5,676)	(2,701)
Amortization of actuarial losses reclassifed to operating and administrative expenses	806	478	1,612	956
Net other comprehensive (losses) earnings	(37,688)	(14,596)	(4,819)	6,502
Ending balance	$ 33,470	$ 36,763	$ 33,470	$ 36,763