Income taxes - Current and Deferred (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Current tax expense									$ 54	$ 6,025	$ 2,824
Deferred tax expense (benefit)									659	(10,035)	9,152
Income tax expense (benefit)	$ (718)	$ (213)	$ (74)	$ 1,718	$ (8,417)	$ (111)	$ 4,390	$ 128	$ 713	$ (4,010)	$ 11,976

Amount of deferred income tax expense (benefit) pertaining to income (loss) from continuing operations.

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Data Type:	xbrli:monetaryItemType
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