Loans Receivable and Other Lending Investments, net - Credit Characteristics by Payment Status (Details) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2020 USD ($) loan	Dec. 31, 2019 USD ($) loan
Greater Than 90 Days
Recorded investment in loans, aged by payment status and presented by class
Financing receivable, number of loans greater than 90 days past due | loan	1	1
Financing receivables, past due time period	11 years	10 years 6 months
Commercial Portfolio Segment
Recorded investment in loans, aged by payment status and presented by class
Current	$ 642,613	$ 665,460
Total Past Due	37,307	37,820
Total	679,920	703,280
Commercial Portfolio Segment | Less Than and Equal to 90 Days
Recorded investment in loans, aged by payment status and presented by class
Total Past Due	0	0
Commercial Portfolio Segment | Greater Than 90 Days
Recorded investment in loans, aged by payment status and presented by class
Total Past Due	37,307	37,820
Commercial Portfolio Segment | Senior mortgages
Recorded investment in loans, aged by payment status and presented by class
Current	512,300	534,765
Total Past Due	37,307	37,820
Total	549,607	572,585
Commercial Portfolio Segment | Senior mortgages | Less Than and Equal to 90 Days
Recorded investment in loans, aged by payment status and presented by class
Total Past Due	0	0
Commercial Portfolio Segment | Senior mortgages | Greater Than 90 Days
Recorded investment in loans, aged by payment status and presented by class
Total Past Due	37,307	37,820
Commercial Portfolio Segment | Corporate/Partnership loans
Recorded investment in loans, aged by payment status and presented by class
Current	119,061	119,818
Total Past Due	0	0
Total	119,061	119,818
Commercial Portfolio Segment | Corporate/Partnership loans | Less Than and Equal to 90 Days
Recorded investment in loans, aged by payment status and presented by class
Total Past Due	0	0
Commercial Portfolio Segment | Corporate/Partnership loans | Greater Than 90 Days
Recorded investment in loans, aged by payment status and presented by class
Total Past Due	0	0
Commercial Portfolio Segment | Subordinate mortgages
Recorded investment in loans, aged by payment status and presented by class
Current	11,252	10,877
Total Past Due	0	0
Total	11,252	10,877
Commercial Portfolio Segment | Subordinate mortgages | Less Than and Equal to 90 Days
Recorded investment in loans, aged by payment status and presented by class
Total Past Due	0	0
Commercial Portfolio Segment | Subordinate mortgages | Greater Than 90 Days
Recorded investment in loans, aged by payment status and presented by class
Total Past Due	$ 0	$ 0