Investments - Additional Information (Detail)	3 Months Ended		6 Months Ended
	Jun. 25, 2016 USD ($) AFS_security	Jun. 27, 2015 USD ($)	Jun. 25, 2016 USD ($) AFS_security	Jun. 27, 2015 USD ($)	Dec. 26, 2015 USD ($)
Investments, Debt and Equity Securities [Abstract]
Total realized gains on sales of AFS securities	$ 2,633,000	$ 27,656,000	$ 11,884,000	$ 43,922,000
Total realized losses on sales of AFS securities	$ 1,442,000	$ 4,787,000	$ 4,997,000	$ 5,679,000
Number of AFS securities issues contributing to total unrealized loss | AFS_security	167		167
Total, unrealized Losses	$ 30,905,000		$ 30,905,000		$ 40,882,000