Fair value measurement - Carrying Amount and Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Tax receivable agreement payable	$ 77,385	$ 77,385
Carrying Amount | Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Term Loan	1,091,949	1,098,303
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Tax receivable agreement payable	48,505	47,625
Fair Value | Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Term Loan	926,343	1,102,295
Fair Value | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Tax receivable agreement payable	0	0
Fair Value | Quoted Prices in Active Markets for Identical Assets (Level 1) | Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Term Loan	0	0
Fair Value | Significant Other Observable Inputs (Level 2)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Tax receivable agreement payable	0	0
Fair Value | Significant Other Observable Inputs (Level 2) | Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Term Loan	926,343	1,102,295
Fair Value | Significant Unobservable Inputs (Level 3)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Tax receivable agreement payable	48,505	47,625
Fair Value | Significant Unobservable Inputs (Level 3) | Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Term Loan	$ 0	$ 0