Cash, Cash Equivalents, and Investments (Detail) - USD ($)	3 Months Ended	6 Months Ended
Jun. 30, 2019	Jul. 01, 2018	Jun. 30, 2019	Jul. 01, 2018
Cash and Cash Equivalents [Abstract]
Gross realized gains on sale of investments	$ 394,000	$ 308,000	$ 458,000	$ 363,000
Gross realized losses on sale of investments	$ 12,000	$ 61,000	$ 36,000	$ 94,000

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