Cash, Cash Equivalents, and Investments (Detail) - USD ($)	3 Months Ended	9 Months Ended
Sep. 29, 2019	Sep. 30, 2018	Sep. 29, 2019	Sep. 30, 2018
Cash and Cash Equivalents [Abstract]
Gross realized gains on sale of investments	$ 361,000	$ 283,000	$ 818,000	$ 646,000
Gross realized losses on sale of investments	$ 67,000	$ 17,000	$ 103,000	$ 111,000

This item represents the gross profit realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities.

No definition available.

Name:	us-gaap_AvailableForSaleSecuritiesGrossRealizedGains
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration