Summary of Significant Accounting Policies (Income Taxes) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Entity Information [Line Items]
Assets with foreclosure elections	$ 31,500
Operating loss carryforwards		$ 460,600
Total income tax (expense) benefit	(235)	(438)	$ (815)
Refund received				$ 3,000
Taxable REIT Subsidiaries
Entity Information [Line Items]
Operating loss carryforwards	38,400	32,500
Assets owned taxable subsidiaries	562,300
Current tax benefit (expense)	(106)	(35)	(447)
Total income tax (expense) benefit	(106)	(35)	(447)
Taxable loss	28,700
Operating loss carryforwards		123,400
Operating loss carryforwards subject to expiration		73,600
Deferred tax assets	80,101	79,645
Valuation allowance	(80,101)	(79,645)
Net deferred tax assets (liabilities)	0	0
Real estate asset basis differences	26,700	32,900
Deferred expenses and other items	12,700	11,900
Other credits	2,300	2,300
REIT
Entity Information [Line Items]
Current tax benefit (expense)	(100)	(400)	(500)
Income taxes paid	$ 800	$ 400	$ 2,000