CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE EARNINGS (Parenthetical) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 25, 2016	Jun. 27, 2015	Jun. 25, 2016	Jun. 27, 2015
Statement of Comprehensive Income [Abstract]
Unrealized gain (loss) on AFS securities, net of income taxes	$ 13,722	$ (444)	$ 20,627	$ (2,466)
Reclassification adjustment for net realized gain on AFS securities, net of income taxes	(460)	(8,837)	(2,661)	(14,778)
Adjustment to postretirement benefit plan obligation, net of income taxes	$ 0	$ 92	$ 0	$ 183