Schedule of Unrealized Loss on Available-for-Sale Investments (Detail) - USD ($) $ in Thousands	Mar. 27, 2021	Dec. 26, 2020
Debt Securities, Available-for-sale [Line Items]
Available-for-sale investments with unrealized losses, Less than 12 months, Fair Value	$ 8,596	$ 3,222
Available-for-sale investments with unrealized losses, Less than 12 months, Unrealized Loss	123	98
Available-for-sale investments with unrealized losses, 12 months or longer, Fair Value	1,810
Available-for-sale investments with unrealized losses, 12 months or longer, Unrealized Loss	32
Available-for-sale investments with unrealized losses, Fair Value, Total	10,406	3,222
Available-for-sale investments with unrealized losses, Unrealized Loss, Total	155	98
Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Available-for-sale investments with unrealized losses, Less than 12 months, Fair Value		541
Available-for-sale investments with unrealized losses, Less than 12 months, Unrealized Loss		26
Available-for-sale investments with unrealized losses, 12 months or longer, Fair Value	555
Available-for-sale investments with unrealized losses, 12 months or longer, Unrealized Loss	11
Available-for-sale investments with unrealized losses, Fair Value, Total	555	541
Available-for-sale investments with unrealized losses, Unrealized Loss, Total	11	26
Corporate bonds and direct obligations of government agencies
Debt Securities, Available-for-sale [Line Items]
Available-for-sale investments with unrealized losses, Less than 12 months, Fair Value	8,596	2,681
Available-for-sale investments with unrealized losses, Less than 12 months, Unrealized Loss	123	72
Available-for-sale investments with unrealized losses, 12 months or longer, Fair Value	1,255
Available-for-sale investments with unrealized losses, 12 months or longer, Unrealized Loss	21
Available-for-sale investments with unrealized losses, Fair Value, Total	9,851	2,681
Available-for-sale investments with unrealized losses, Unrealized Loss, Total	$ 144	$ 72