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Concentrations of risk and geographic information - Narrative (Details) - USD ($)
$ in Thousands
3 Months Ended
Mar. 31, 2020
Mar. 31, 2019
Dec. 31, 2019
Revenue, Major Customer [Line Items]      
Revenue $ 119,400 $ 242,708  
Document Period End Date Mar. 31, 2020    
United States [Member]      
Revenue, Major Customer [Line Items]      
Revenue $ 45,700 $ 83,000  
JAPAN      
Revenue, Major Customer [Line Items]      
Revenue 14,300    
Outside the United States [Member]      
Revenue, Major Customer [Line Items]      
Long-lived assets $ 9,000   $ 11,000