Accumulated Other Comprehensive Earnings (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 28, 2013	Dec. 29, 2012	Dec. 31, 2011
Accumulated Other Comprehensive Income (loss), Net of Tax [Roll Forward]
Balances at beginning of period	$ 38,289	$ 30,261	$ 38,226
Unrealized gain on AFS securities	65,861	19,956	10,041
Net realized gain on AFS securities reclassified to investment income, net	(29,311)	(6,373)	(12,202)
Amortization of actuarial loss reclassified to operating and administrative expenses	12,160	(5,555)	(5,804)
Net other comprehensive earnings	48,710	8,028	(7,965)
Balances at end of period	86,999	38,289	30,261
AFS Securities
Accumulated Other Comprehensive Income (loss), Net of Tax [Roll Forward]
Balances at beginning of period	58,286	44,703	46,864
Unrealized gain on AFS securities	65,861	19,956	10,041
Net realized gain on AFS securities reclassified to investment income, net	(29,311)	(6,373)	(12,202)
Net other comprehensive earnings	36,550	13,583	(2,161)
Balances at end of period	94,836	58,286	44,703
Postretirement Benefits
Accumulated Other Comprehensive Income (loss), Net of Tax [Roll Forward]
Balances at beginning of period	(19,997)	(14,442)	(8,638)
Amortization of actuarial loss reclassified to operating and administrative expenses	12,160	(5,555)	(5,804)
Net other comprehensive earnings	12,160	(5,555)	(5,804)
Balances at end of period	$ (7,837)	$ (19,997)	$ (14,442)