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Cash, Cash Equivalents, and Investments - Additional Information (Detail) (USD $) | 3 Months Ended | 6 Months Ended |
--- | --- | --- | ---
Jun. 30, 2013 | Jul. 01, 2012 | Jun. 30, 2013 | Jul. 01, 2012 | Jun. 30, 2013 Equity Securities [Member] | Dec. 31, 2012 Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items] |  |  |  |  |  |
Fair value |  |  |  |  | $ 1,669,000 | $ 2,131,000
Gross unrealized loss |  |  | 462,000 |  | 462,000 |
Gross realized gains on sale of investments | 101,000 | 1,233,000 | 150,000 | 1,327,000 |  |
Gross realized losses on sale of investments | 49,000 | 238,000 | 67,000 | 238,000 |  |
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 |  |  |  |  |

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