Summary of Significant Accounting Policies - Reclassifications (Details) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($) loan	Dec. 31, 2017 USD ($)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Rental income	$ 400		$ 1,200
Rent and tenant receivables and other assets, net		$ 7,844		$ 3,264
Investment in unconsolidated entities		34,293		39,520
Return of investment from unconsolidated entities		48	1,141
Net cash provided by (used in) operating activities		433,657	595,356
Net cash (used in) provided by investing activities		197,796	(57,221)
Net cash provided by (used in) financing activities		$ (642,776)	(757,445)
Accounting Standards Update 2016-18 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net cash (used in) provided by investing activities			14,600
Net cash provided by (used in) financing activities			$ (2,600)
Number of mortgage loans, satisfied by foreclosure or execution of deed | loan			2
Distributions Received From Equity method Investments [Member] | Accounting Standards Update 2016-15 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net cash provided by (used in) operating activities			$ (1,100)
Net cash (used in) provided by investing activities			1,100
Proceeds From Settlement Of Insurance Claims [Member] | Accounting Standards Update 2016-15 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net cash provided by (used in) operating activities			(100)
Net cash (used in) provided by investing activities			100
Reclassification [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Direct financing lease income reclassed	$ 400		$ 1,200
Investment in unconsolidated entities				$ 3,300