Schedule of Unrealized Loss on Available for Sale Investments (Detail) - USD ($) $ in Thousands	Jul. 01, 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	$ 42,329	$ 42,906
Available-for-sale investments with unrealized losses, Less than 12 months, Unrealized Loss	134	207
Available-for-sale investments with unrealized losses, 12 months or longer, Fair Value	3,629	3,681
Available-for-sale investments with unrealized losses, 12 months or longer, Unrealized Loss	37	57
Available-for-sale investments with unrealized losses, Fair Value, Total	45,958	46,587
Available-for-sale investments with unrealized losses, Unrealized Loss, Total	171	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	1,097	1,363
Available-for-sale investments with unrealized losses, Less than 12 months, Unrealized Loss	1	6
Available-for-sale investments with unrealized losses, 12 months or longer, Fair Value	1,353	2,314
Available-for-sale investments with unrealized losses, 12 months or longer, Unrealized Loss	4	13
Available-for-sale investments with unrealized losses, Fair Value, Total	2,450	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	29,252	28,809
Available-for-sale investments with unrealized losses, Less than 12 months, Unrealized Loss	125	195
Available-for-sale investments with unrealized losses, 12 months or longer, Fair Value	2,276	1,367
Available-for-sale investments with unrealized losses, 12 months or longer, Unrealized Loss	33	44
Available-for-sale investments with unrealized losses, Fair Value, Total	31,528	30,176
Available-for-sale investments with unrealized losses, Unrealized Loss, Total	158	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	11,980	12,734
Available-for-sale investments with unrealized losses, Less than 12 months, Unrealized Loss	8	6
Available-for-sale investments with unrealized losses, Fair Value, Total	11,980	12,734
Available-for-sale investments with unrealized losses, Unrealized Loss, Total	$ 8	$ 6