Cash, Cash Equivalents, and Investments (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Oct. 01, 2017	Oct. 02, 2016	Oct. 01, 2017	Oct. 02, 2016
Cash and Cash Equivalents [Abstract]
Gross realized gains on sale of investments	$ 306,000	$ 55,000	$ 449,000	$ 280,000
Gross realized losses on sale of investments	$ 43,000	$ 0	$ 79,000	$ 97,000