Schedule of Unrealized Loss on Available-for-Sale Investments (Detail) - USD ($) $ in Thousands	Dec. 30, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale investments with unrealized losses, Less than 12 months, Fair Value	$ 43,186	$ 42,906
Available-for-sale investments with unrealized losses, Less than 12 months, Unrealized Loss	224	207
Available-for-sale investments with unrealized losses, 12 months or longer, Fair Value	14,648	3,681
Available-for-sale investments with unrealized losses, 12 months or longer, Unrealized Loss	116	57
Available-for-sale investments with unrealized losses, Fair Value, Total	57,834	46,587
Available-for-sale investments with unrealized losses, Unrealized Loss, Total	340	264
Asset-backed securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale investments with unrealized losses, Less than 12 months, Fair Value	1,864	1,363
Available-for-sale investments with unrealized losses, Less than 12 months, Unrealized Loss	4	6
Available-for-sale investments with unrealized losses, 12 months or longer, Fair Value	632	2,314
Available-for-sale investments with unrealized losses, 12 months or longer, Unrealized Loss	1	13
Available-for-sale investments with unrealized losses, Fair Value, Total	2,496	3,677
Available-for-sale investments with unrealized losses, Unrealized Loss, Total	5	19
Corporate bonds and direct obligations of government agencies
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale investments with unrealized losses, Less than 12 months, Fair Value	41,322	28,809
Available-for-sale investments with unrealized losses, Less than 12 months, Unrealized Loss	220	195
Available-for-sale investments with unrealized losses, 12 months or longer, Fair Value	14,016	1,367
Available-for-sale investments with unrealized losses, 12 months or longer, Unrealized Loss	115	44
Available-for-sale investments with unrealized losses, Fair Value, Total	55,338	30,176
Available-for-sale investments with unrealized losses, Unrealized Loss, Total	$ 335	239
U.S. Treasury obligations
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale investments with unrealized losses, Less than 12 months, Fair Value		12,734
Available-for-sale investments with unrealized losses, Less than 12 months, Unrealized Loss		6
Available-for-sale investments with unrealized losses, Fair Value, Total		12,734
Available-for-sale investments with unrealized losses, Unrealized Loss, Total		$ 6