CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE EARNINGS (Parenthetical) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 24, 2016	Sep. 26, 2015	Sep. 24, 2016	Sep. 26, 2015
Statement of Comprehensive Income [Abstract]
Unrealized gain (loss) on AFS securities, net of income taxes	$ 13,390	$ (36,921)	$ 34,017	$ (39,387)
Reclassification adjustment for net realized gain on AFS securities, net of income taxes	(2,346)	(5,614)	(5,007)	(20,392)
Adjustment to postretirement benefit plan obligation, net of income taxes	$ 0	$ 91	$ 0	$ 274