Schedule of Unrealized Loss on Available for Sale Investments (Detail) - USD ($) $ in Thousands	Apr. 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	$ 46,194	$ 42,906
Available-for-sale investments with unrealized losses, Less than 12 months, Unrealized Loss	168	207
Available-for-sale investments with unrealized losses, 12 months or longer, Fair Value	3,617	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	49,811	46,587
Available-for-sale investments with unrealized losses, Unrealized Loss, Total	205	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	1,268	1,363
Available-for-sale investments with unrealized losses, Less than 12 months, Unrealized Loss	2	6
Available-for-sale investments with unrealized losses, 12 months or longer, Fair Value	2,240	2,314
Available-for-sale investments with unrealized losses, 12 months or longer, Unrealized Loss	9	13
Available-for-sale investments with unrealized losses, Fair Value, Total	3,508	3,677
Available-for-sale investments with unrealized losses, Unrealized Loss, Total	11	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	32,190	28,809
Available-for-sale investments with unrealized losses, Less than 12 months, Unrealized Loss	155	195
Available-for-sale investments with unrealized losses, 12 months or longer, Fair Value	1,377	1,367
Available-for-sale investments with unrealized losses, 12 months or longer, Unrealized Loss	28	44
Available-for-sale investments with unrealized losses, Fair Value, Total	33,567	30,176
Available-for-sale investments with unrealized losses, Unrealized Loss, Total	183	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	12,736	12,734
Available-for-sale investments with unrealized losses, Less than 12 months, Unrealized Loss	11	6
Available-for-sale investments with unrealized losses, Fair Value, Total	12,736	12,734
Available-for-sale investments with unrealized losses, Unrealized Loss, Total	$ 11	$ 6