Accumulated Other Comprehensive Earnings (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 29, 2014	Mar. 30, 2013
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Balances at Beginning of Period	$ 86,999	$ 38,289
Unrealized gain on AFS securities	11,913	33,695
Net realized gain on AFS securities reclassified to investment income, net	(3,437)	(1,632)
Amortization of actuarial losses reclassified to operating and administrative expenses	84	806
Net other comprehensive earnings	8,560	32,869
Balances at End of Period	95,559	71,158
AFS Securities
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Balances at Beginning of Period	94,836	58,286
Unrealized gain on AFS securities	11,913	33,695
Net realized gain on AFS securities reclassified to investment income, net	(3,437)	(1,632)
Net other comprehensive earnings	8,476	32,063
Balances at End of Period	103,312	90,349
Postretirement Benefits
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Balances at Beginning of Period	(7,837)	(19,997)
Amortization of actuarial losses reclassified to operating and administrative expenses	84	806
Net other comprehensive earnings	84	806
Balances at End of Period	$ (7,753)	$ (19,191)