Debt and Preferred Equity Investments - Narrative (Details)	1 Months Ended	12 Months Ended
	Sep. 30, 2014 USD ($)	Dec. 31, 2017 USD ($) segment	Dec. 31, 2016 USD ($) segment
Preferred equity investment
Carrying Value		$ 2,114,041,000	$ 1,640,412,000
Number of portfolio segments of financial receivables (segment) | segment		1	1
Additional amount of financing receivables included in other assets		$ 65,500,000	$ 99,500,000
Junior Mortgage Participation Acquired in September 2014
Preferred equity investment
Payments to acquire loans receivable	$ 0
Carrying Value		$ 0