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Stockholders' equity - Additional Information (Detail) - USD ($)
$ in Millions
3 Months Ended 6 Months Ended
Jun. 30, 2019
Jun. 30, 2020
Jun. 30, 2019
Dec. 31, 2019
Dec. 31, 2018
Accumulated Other Comprehensive Income Loss [Line Items]          
Number of shares authorized for repurchase         2,000,000.0
Shares available for repurchase under the plan   1,563,519   1,686,008  
Aggregate purchase price $ 1.4 $ 1.0 $ 1.4    
Treasury stock          
Accumulated Other Comprehensive Income Loss [Line Items]          
Stock repurchased and acquired in market transactions   122,489      
Aggregate purchase price $ 1.4 $ 1.0 $ 1.4