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Investments in debt and equity securities (Detail) - USD ($)
$ in Thousands
Mar. 31, 2021
Dec. 31, 2020
Investment Holdings [Line Items]    
Debt securities $ 8,221 $ 8,217
Investments in equity securities 34,730 44,077
Total 42,951 52,294
Debt securities, short-term investments 8,221 8,217
Total, short-term investments 11,060 20,101
Debt securities, long-term investments 0 0
Total, long-term investments 31,891 32,193
Certificates of deposit and other time deposits    
Investment Holdings [Line Items]    
Debt securities 8,221 8,217
Investments in equity securities 0 0
Total 8,221 8,217
Investments in mutual funds and common stock    
Investment Holdings [Line Items]    
Debt securities 0 0
Investments in equity securities 34,730 44,077
Total 34,730 44,077
Short-term Investments    
Investment Holdings [Line Items]    
Investments in equity securities 2,839 11,884
Long-term Investments    
Investment Holdings [Line Items]    
Investments in equity securities $ 31,891 $ 32,193