Changes in Accumulated Other Comprehensive Income Balances (Parenthetical) (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 28, 2014	Sep. 29, 2013	Sep. 28, 2014	Sep. 29, 2013	Dec. 31, 2013
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income before reclassifications, tax	$ (139)	$ 358	$ 1,103	$ (367)
Other comprehensive income before reclassifications, tax			0
Amounts reclassified from accumulated other comprehensive income, tax	(348)	(109)	(591)	(231)
Amounts reclassified from accumulated other comprehensive income, tax	(42)	(40)	(127)	(119)
Unrealized gains on marketable securities, tax	1,306		1,306		794
Retirement plans prior service benefit, tax	(411)		(411)		(284)
Unrealized Gains on Marketable Securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income before reclassifications, tax			1,103
Amounts reclassified from accumulated other comprehensive income, tax			(591)
Retirement Plans Prior Service Benefit
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income before reclassifications, tax			0
Amounts reclassified from accumulated other comprehensive income, tax			$ (127)