Recently Issued Accounting Literature (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Jun. 30, 2020	Dec. 31, 2019	Jun. 30, 2019	Dec. 31, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accounting Standards Update [Extensible List]			us-gaap:AccountingStandardsUpdate201613Member
Stockholders' equity	$ 6,885,685	$ 7,710,256	$ 6,885,685	$ 7,710,256	$ 6,928,909	$ 7,310,978	$ 7,496,144	$ 5,107,883
Credit losses on loans receivable	0	0	13,369	0
Earnings Less Than Distributions
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Stockholders' equity	$ (2,463,635)	$ (1,649,035)	$ (2,463,635)	$ (1,649,035)	$ (2,415,500)	(1,954,266)	$ (1,845,995)	$ (4,167,184)
Cumulative Effect, Period of Adoption, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Stockholders' equity						(16,064)
Cumulative Effect, Period of Adoption, Adjustment | Earnings Less Than Distributions
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Stockholders' equity						$ (16,064)