Marketable Securities - Schedule of Market Value, Cost and Unrealized Gains on Equity Securities (Detail) - USD ($) $ in Thousands	Sep. 29, 2018	Dec. 31, 2017
Investments Debt And Equity Securities [Abstract]
Marketable securities	$ 10,433	$ 15,144
Cost	8,010	10,231
Unrealized gain	$ 2,423	$ 4,913

This item represents the cost of equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments for other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

No definition available.

Name:	us-gaap_AvailableForSaleEquitySecuritiesAmortizedCostBasis
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant