Changes in Accumulated Other Comprehensive Income Balances (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
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance			$ 4,000
Other comprehensive income before reclassifications, net of tax			2,166
Amounts reclassified from accumulated other comprehensive income, net of tax	(712)	(258)	(1,307)	(608)
Other comprehensive income (loss)	(850)	365	859	(1,248)
Ending balance	4,859		4,859
Unrealized Gains on Marketable Securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance			1,381
Other comprehensive income before reclassifications, net of tax			2,166
Amounts reclassified from accumulated other comprehensive income, net of tax			(1,086)
Other comprehensive income (loss)			1,080
Ending balance	2,461		2,461
Retirement Plans Prior Service Benefit
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance			2,619
Amounts reclassified from accumulated other comprehensive income, net of tax			(221)
Other comprehensive income (loss)			(221)
Ending balance	$ 2,398		$ 2,398