Segment Reporting Segment Reporting (Details 2) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting [Abstract]
Rental income from real estate assets sold or held for sale	$ 23,457	$ 70,273	$ 96,297
Operating expenses from real estate assets sold or held for sale	(8,884)	(26,010)	(36,914)
Net operating income from real estate assets sold or held for sale	$ 14,573	$ 44,263	$ 59,383