Income taxes - Current and Deferred (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Current tax expense									$ 145	$ 54	$ 6,025
Deferred tax expense (benefit)									7,963	659	(10,035)
Income Tax Expense (Benefit)	$ 3,728	$ 652	$ 3,309	$ 419	$ (718)	$ (213)	$ (74)	$ 1,718	$ 8,108	$ 713	$ (4,010)