Dispositions but not discontinued operations (Details) - Disposal Group, Disposed of by Sale, Not Discontinued Operations - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Revenues:
Total revenues	$ 35,236	$ 60,241	$ 78,459	$ 135,348
Expenses:
Interest expense	120	1,540	264	4,266
Property operating expenses	22,364	22,365	45,516	46,606
Provision for depreciation	2,555	12,455	6,874	24,749
Total expenses	25,039	36,360	52,654	75,621
Income (loss) from real estate dispositions, net	$ 10,197	$ 23,881	$ 25,805	$ 59,727