Debt and Preferred Equity Investments (Narrative)(Details)	6 Months Ended
	Jun. 30, 2017 USD ($) segment	Jun. 30, 2016 segment	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Preferred equity investment
Carrying Value	$ 1,986,413,000		$ 1,640,412,000
Number of portfolio segments of financial receivables (segment) | segment	1	1
Additional amount of financing receivables included in other assets	$ 94,900,000		99,500,000
Junior Mortgage Participation Acquired in September 2014
Preferred equity investment
Carrying Value	$ 0		$ 0	$ 0