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Marketable securities (Detail) - USD ($)
Mar. 31, 2023
Dec. 31, 2022
Amortized cost / Cost    
Marketable securities $ 80,100,000 $ 70,494,000
Unrealized gains    
Marketable securities 4,000 0
Unrealized losses    
Marketable securities (892,000) (1,759,000)
Fair value    
Marketable securities 79,212,000 68,735,000
Debt securities, available-for-sale, noncurrent 0 0
U.S. government agency securities and treasuries    
Amortized cost / Cost    
Debt securities 79,600,000 67,970,000
Unrealized gains    
Debt securities 4,000 0
Unrealized losses    
Debt securities (883,000) (1,733,000)
Fair value    
Debt securities 78,721,000 66,237,000
Corporate bonds    
Amortized cost / Cost    
Debt securities 500,000 2,524,000
Unrealized gains    
Debt securities 0 0
Unrealized losses    
Debt securities (9,000) (26,000)
Fair value    
Debt securities $ 491,000 $ 2,498,000