Dispositions but not discontinued operations (Details) - Disposal Group, Disposed of by Sale, Not Discontinued Operations - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Revenues:
Total revenues	$ 29,035	$ 52,584	$ 92,447	$ 175,934
Expenses:
Interest expense	18	1,243	261	5,514
Property operating expenses	21,312	19,147	59,640	58,525
Provision for depreciation	801	10,999	6,605	33,806
Total expenses	22,131	31,389	66,506	97,845
Income (loss) from real estate dispositions, net	$ 6,904	$ 21,195	$ 25,941	$ 78,089