Income taxes - Income tax (benefit) expense (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended	12 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2019	Dec. 31, 2019	Dec. 31, 2018
Current:
Foreign				$ 316	$ 81
Current Income Tax Expense (Benefit), Total				316	81
Deferred:
Foreign				(8,611)	(255)
Deferred Income Tax Expense (Benefit), Total		$ (525)	$ (522)	(8,611)	(255)
Income tax (benefit) expense	$ (197)	$ (167)	$ (364)	$ (8,295)	$ (174)