Dispositions and Assets Held for Sale (Dispositions and Assets Held for Sale) (Details) - Disposal Group, Disposed of by Sale, Not Discontinued Operations - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenues:
Total revenues	$ 148,725	$ 275,087	$ 565,450
Expenses:
Interest expense	294	6,655	52,675
Property operating expenses	81,698	81,182	89,666
Provision for depreciation	16,900	55,294	122,153
Total expenses	98,892	143,131	264,494
Income (loss) from real estate dispositions, net	$ 49,833	$ 131,956	$ 300,956