Schedule IV - Mortgage Loans on Real Estate - Reconciliation of Mortgage Loans on Real Estate (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
SEC Schedule, 12-29, Real Estate Companies, Investment in Movement in Mortgage Loans on Real Estate [Roll Forward]
Balance at January 1	$ 752,129	$ 915,905	$ 934,964
Additions:
New mortgage loans	381,133	265,966	25,893
Additions under existing mortgage loans	157,702	132,703	165,275
Other	25,778	23,388	30,694
Deductions:
Collections of principal	(501,466)	(528,321)	(247,431)
Recovery of (provision for) loan losses	(45)	28	9,747
Transfers to real estate and equity investments	(84,684)	(57,505)	(3,177)
Amortization of premium	(32)	(35)	(60)
Balance at December 31	$ 730,515	752,129	915,905
Charge offs		$ 1,200	$ 10,100