Dispositions and Real Property Held for Sale (Summary of Activity Related to Dispositions and Assets Held for Sale) (Details) - Disposal Group, Disposed of by Sale, Not Discontinued Operations - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Revenues:
Total revenues	$ 257,089	$ 712,529	$ 916,896
Expenses:
Interest expense	6,665	18,506	18,801
Property operating expenses	134,119	375,327	495,770
Provision for depreciation	55,114	138,041	189,909
Total expenses	195,898	531,874	704,480
Income (loss) from real estate dispositions, net	$ 61,191	$ 180,655	$ 212,416