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Income taxes (Details)
shares in Thousands, $ in Thousands
12 Months Ended
Dec. 31, 2018
USD ($)
shares
Income Tax Contingency [Line Items]  
Uncertain tax positions $ 0
LLC Units  
Income Tax Contingency [Line Items]  
Redemption of LLC Units (in shares) | shares 261
Tax Receivable Agreement  
Income Tax Contingency [Line Items]  
Percentage due to related parties 85.00%
Pre-IPO LLC Members | Tax Receivable Agreement  
Income Tax Contingency [Line Items]  
Percentage due to related parties 85.00%
Due to related parties $ 1,700
Due to related parties, current $ 9