Investments Available for Sale Securities Reconciliation (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 30, 2017
Schedule of Available-for-sale Securities [Line Items]
Cost	$ 3,700,638	$ 3,926,697
Gross Unrealized Gains	425	1,297
Gross Unrealized Losses	73,117	41,863
Fair Value	3,627,946	3,886,131
Nontaxable Municipal Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	1,677,884	1,811,523
Gross Unrealized Gains	187	602
Gross Unrealized Losses	20,095	16,420
Fair Value	1,657,976	1,795,705
Fixed Income Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	2,022,754	2,115,174
Gross Unrealized Gains	238	695
Gross Unrealized Losses	53,022	25,443
Fair Value	$ 1,969,970	$ 2,090,426