Reconciliation of income and expenses (Details 3) - 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 Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Income (loss) from discontinued operations	$ 261	$ 1,509	$ (1,320)	$ (163)	$ 2,846	$ (118)	$ (273)	$ 477	$ 287	$ 2,932	$ (3,783)
Discontinued operations, held-for-sale or disposed by sale
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Operating revenues									103	(459)	465
Operating expenses									290	921	(4,607)
Operating income (loss)									(187)	(1,380)	5,072
Other income									0	12
Other expense											(13)
Interest expense									0	575	250
Income (loss) from discontinued operations before income taxes									(187)	(1,943)	4,809
Income taxes									(474)	(4,875)	8,592
Income (loss) from discontinued operations									$ 287	$ 2,932	$ (3,783)