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Cash, Cash Equivalents, and Investments (Detail) - USD ($)
3 Months Ended 6 Months Ended
Jun. 30, 2019
Jul. 01, 2018
Jun. 30, 2019
Jul. 01, 2018
Cash and Cash Equivalents [Abstract]        
Gross realized gains on sale of investments $ 394,000 $ 308,000 $ 458,000 $ 363,000
Gross realized losses on sale of investments $ 12,000 $ 61,000 $ 36,000 $ 94,000