Cash, Cash Equivalents, and Investments - Additional Information (Detail) (USD $)	3 Months Ended			9 Months Ended
	Sep. 29, 2013	Jun. 30, 2013	Sep. 30, 2012	Sep. 29, 2013	Sep. 30, 2012	Sep. 29, 2013 Equity Securities [Member]	Dec. 31, 2012 Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross realized gains on sale of investments	$ 32,000		$ 342,000	$ 182,000	$ 1,669,000
Gross realized losses on sale of investments	12,000		1,000	79,000	239,000
Fair value						1,864,000	2,131,000
Net unrealized loss				267,000		267,000
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, 2013
Number of contributions made during the period				0
Cash distribution received		$ 1,285,000