Schedule IV - Mortgage Loans on Real Estate (Reconciliation of mortgage loans) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Reconciliation of mortgage loans:
Balance at beginning of year	$ 145,686	$ 249,071	$ 306,120
Additions:
New mortgage loans	193,505	0	25,290
Draws on existing loans	20,844	45,961	36,458
Total additions	214,349	45,961	61,748
Deductions:
Collections of principal	(17,019)	(87,249)	(116,905)
Loan balance transferred to non-real estate loans receivable	(53,071)	(64,040)	0
Change in allowance for credit losses and charge-offs	(5,645)	0	0
Other	(329)	0	0
Total deductions	(76,064)	(151,289)	(116,905)
Change in balance due to foreign currency translation	(9,781)	(1,944)	1,892
Balance at end of year	$ 293,752	$ 145,686	$ 249,071