Summary of Fair Value Measurements for Available for Sale Securities (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 26, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of available-for-sale securities	$ 6,738,618	$ 6,602,934
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of available-for-sale securities	1,286,625	1,049,791
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of available-for-sale securities	5,451,993	5,553,143
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of available-for-sale securities	$ 0	$ 0