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Income taxes - Additional information (Details) - USD ($)
$ in Thousands
3 Months Ended 6 Months Ended
Jun. 30, 2019
Jun. 30, 2019
Jan. 01, 2018
Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]        
Adjustments to accumulated deficit for new accounting pronouncements       $ (1,824)
Decrease to the amounts of uncertain tax positions previously determined $ 0      
Increase to the amounts of uncertain tax positions previously determined   $ 0    
Accounting Standards Update 2016-16        
New Accounting Pronouncements or Change in Accounting Principle [Line Items]        
Adjustments to accumulated deficit for new accounting pronouncements     $ 1,800