Schedule IV - Mortgage Loans on Real Estate Schedule IV - Mortgage Loans on Real Estate (Roll-Forward) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Schedule IV - Mortgage Loans on Real Estate [Abstract]
Mortgage Loans on Real Estate, January 1	$ 294,120,000	$ 202,877,000	$ 98,110,000
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate, New Mortgage Loan	55,059,000	105,345,000	108,266,000
Amortization of Deferred Charges	806,000	440,000	608,000
Mortgage Loans On Real Estate Total Additions	55,865,000	105,785,000	108,874,000
Note Receivable, Commitment Fees, Received	222,000	108,000	1,800,000
Settlement of mortgage note by real estate acquisition	63,220,000	14,000,000	0
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate, Collections of Principal	27,052,000	434,000	2,307,000
Mortgage Loans On Real Estate, Total Deductions	90,494,000	14,542,000	4,107,000
Mortgage Loans on Real Estate, December 31	259,491,000	294,120,000	202,877,000
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate, Gross	3,265,070,000	3,074,846,000	2,818,365,000	$ 2,665,903,000
Noncontrolling Interest, Noncash Increase from Subsidiary Equity Issuance	$ 10,778,000	$ 0	$ 0