Changes in Accumulated Other Comprehensive Income Balances (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended			9 Months Ended
	Sep. 29, 2013		Sep. 30, 2012	Sep. 29, 2013		Sep. 30, 2012
Other Comprehensive Income (Loss) [Line Items]
Beginning balance				$ 5,820	[1]
Other comprehensive income before reclassifications				(1,019)
Amounts reclassified from accumulated other comprehensive income	(311)		(185)	(946)		(858)
Other comprehensive income (loss)	576		1,074	(1,965)		1,597
Ending balance	3,855	[1]		3,855	[1]
Unrealized Gains on Marketable Securities
Other Comprehensive Income (Loss) [Line Items]
Beginning balance				2,925	[1]
Other comprehensive income before reclassifications				(1,019)
Amounts reclassified from accumulated other comprehensive income				(621)
Other comprehensive income (loss)				(1,640)
Ending balance	1,285	[1]		1,285	[1]
Retirement Plans Prior Service Credit
Other Comprehensive Income (Loss) [Line Items]
Beginning balance				2,895	[1]
Amounts reclassified from accumulated other comprehensive income				(325)
Other comprehensive income (loss)				(325)
Ending balance	$ 2,570	[1]		$ 2,570	[1]

[1] Net of tax of $835 for unrealized gains on marketable securities and $(125) for retirement plans prior service credit.