Loans Receivable and Other Lending Investments, net (Credit Characteristics for Performing Loans) (Details) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Recorded Investments in loans, presented by class and by credit quality, as indicated by risk rating
Loans	$ 1,385,935	$ 1,463,003
Senior mortgages
Recorded Investments in loans, presented by class and by credit quality, as indicated by risk rating
Loans	839,174	945,182
Corporate/Partnership loans
Recorded Investments in loans, presented by class and by credit quality, as indicated by risk rating
Loans	521,462	492,823
Subordinate mortgages
Recorded Investments in loans, presented by class and by credit quality, as indicated by risk rating
Loans	25,299	24,998
Real Estate Finance
Recorded Investments in loans, presented by class and by credit quality, as indicated by risk rating
Loans	$ 1,135,134	$ 1,209,062
Weighted Average Risk Ratings	2.55	3.11
Real Estate Finance | Senior mortgages
Recorded Investments in loans, presented by class and by credit quality, as indicated by risk rating
Loans	$ 756,720	$ 859,250
Weighted Average Risk Ratings	2.31	3.12
Real Estate Finance | Corporate/Partnership loans
Recorded Investments in loans, presented by class and by credit quality, as indicated by risk rating
Loans	$ 364,159	$ 335,677
Weighted Average Risk Ratings	3.06	3.09
Real Estate Finance | Subordinate mortgages
Recorded Investments in loans, presented by class and by credit quality, as indicated by risk rating
Loans	$ 14,255	$ 14,135
Weighted Average Risk Ratings	2.46	3.00