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Fair Value Measurements and Long-term Investments - Additional Information (Detail) - USD ($)
$ in Thousands
3 Months Ended 9 Months Ended
Sep. 30, 2019
Sep. 30, 2018
Sep. 30, 2019
Sep. 30, 2018
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]        
Impairment recoveries     $ 1,000  
Non-cash impairment charges of investments $ 0 $ 0 $ (1,045) $ 15,487
1.25% Cash Convertible Senior Notes [Member]        
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]        
Interest rate 1.25%   1.25%  
Other Assets [Member]        
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]        
Convertible note carrying value $ 6,000   $ 6,000