Marketable Securities - Summary of Net Realized Gains on Marketable Equity Securities (Detail) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 29, 2018	Sep. 30, 2017	Sep. 29, 2018	Sep. 30, 2017
Realized gain
Sale proceeds	$ 2,804	$ 725	$ 5,615	$ 1,261
Cost of securities sold	2,439	106	5,123	338
Realized gain	365	619	492	923
Realized gain, net of taxes	$ 275	$ 388	$ 368	$ 565

This item represents the difference between the gross realized gains and losses realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities. Additionally, this item would include any losses recognized for other than temporary impairments (OTTI) of the subject investments in debt and equity securities.

No definition available.

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