Loans Receivable and Other Lending Investments, net (Credit Characteristics for Performing Loans) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Recorded Investments in loans, presented by class and by credit quality, as indicated by risk rating
Performing Loans	$ 870,992	$ 1,216,332
Real Estate Finance
Recorded Investments in loans, presented by class and by credit quality, as indicated by risk rating
Performing Loans	$ 857,662	$ 1,056,944
Weighted Average Risk Ratings	2.77	2.77
Real Estate Finance | Senior mortgages
Recorded Investments in loans, presented by class and by credit quality, as indicated by risk rating
Performing Loans	$ 697,807	$ 713,057
Weighted Average Risk Ratings	2.76	2.72
Real Estate Finance | Corporate/Partnership loans
Recorded Investments in loans, presented by class and by credit quality, as indicated by risk rating
Performing Loans	$ 149,663	$ 334,364
Weighted Average Risk Ratings	2.84	2.85
Real Estate Finance | Subordinate mortgages
Recorded Investments in loans, presented by class and by credit quality, as indicated by risk rating
Performing Loans	$ 10,192	$ 9,523
Weighted Average Risk Ratings	3.00	3.00