Summary of significant accounting policies - Contract Balances (Details) - USD ($) $ in Thousands |
3 Months Ended | 6 Months Ended | |||
---|---|---|---|---|---|
Jun. 30, 2021 |
Jun. 30, 2020 |
Jun. 30, 2021 |
Jun. 30, 2020 |
Dec. 31, 2020 |
|
Accounting Policies [Abstract] | |||||
Contract with customer, asset | $ 1,600 | $ 1,600 | $ 900 | ||
Contract With Customer, Liability [Roll Forward] | |||||
Balance, beginning of the period | 221,579 | $ 145,312 | 205,509 | $ 140,449 | |
Revenue earned | (66,967) | (49,393) | (111,398) | (91,395) | |
Deferral of revenue | 83,845 | 61,363 | 144,346 | 108,228 | |
Balance, end of the period | $ 238,457 | $ 157,282 | $ 238,457 | $ 157,282 |