Property and equipment (Narrative) (Details) - USD ($) $ in Thousands		1 Months Ended	3 Months Ended	9 Months Ended	12 Months Ended
	Aug. 29, 2019	Jun. 30, 2019	Mar. 21, 2017	Dec. 31, 2017	Dec. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment [Abstract]
Impairment loss on building and adjacent land housing		$ 6,407			$ 6,407
Proceeds from asset dispositions	$ 11,494		$ 1,884	$ 189,735	14,667	$ 50,523
Loss on extinguishment of debt	$ 1,624		$ 0	$ 635	1,624	$ 0
Impairment loss on assets held for sale					$ 781