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Stockholders' equity - Additional Information (Details) - $ / shares
Dec. 31, 2020
Dec. 31, 2019
Equity [Abstract]    
Common stock, shares authorized (in shares) 150,000,000 150,000,000.0
Common stock, par value (in dollars per share) $ 0.01 $ 0.01
Preferred stock, shares authorized (in shares) 40,000,000  
Preferred stock, par value (in dollars per share) $ 1  
Unissued common stock reserved for stock-based incentive plans and convertible debt (in shares) 18,700,000