Cash, Cash Equivalents, and Investments - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended
	Sep. 28, 2014	Sep. 29, 2013	Sep. 28, 2014	Sep. 29, 2013
Amortized Cost And Fair Value Debt Securities [Abstract]
Gross realized gains on sale of investments	$ 66,000	$ 32,000	$ 695,000	$ 182,000
Gross realized losses on sale of investments	21,000	12,000	44,000	79,000
Maximum amount committed to invest in limited partnership			20,500,000
Contribution to limited partnership	19,886,000		19,886,000
Remaining amount of commitment in limited partnership	614,000		614,000
Investment expiration date			Dec. 31, 2015
Number of contributions made during the period			0
Distributions From Partnership During Period			$ 0