SCHEDULE IV - MORTGAGE LOANS ON REAL ESTATE (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2018
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Prior Liens				$ 0
Principal Balance	$ 16,033	$ 39,026	$ 241,038	23,146
Book Value				23,206
Aggregate cost for federal income tax purposes				23,300
SEC Schedule, 12-29, Real Estate Companies, Investment in Movement in Mortgage Loans on Real Estate [Roll Forward]
Balance at the beginning of the year	16,033	39,026	241,038
Additions during period:
Draws	10,943	1,738	0
New mortgage loans	0	12,987	3,767
Interest income added to principal	1,528	539	690
Deductions during period:
Paydowns/repayments	(5,358)	(14,570)	(193,075)
Conversion to real property	0	(19,085)	(10,100)
Write-offs	0	(4,602)	(3,294)
Balance at the end of the year	$ 23,146	$ 16,033	$ 39,026
Mortgages | River Vista
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Contractual Interest Rate	10.00%
Prior Liens				0
Principal Balance	$ 18,577			18,577
Book Value				18,577
Deductions during period:
Balance at the end of the year	$ 18,577
Construction Mortgages | McKinney
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Contractual Interest Rate	8.00%
Prior Liens				0
Principal Balance	$ 3,513			3,513
Book Value				3,551
Deductions during period:
Balance at the end of the year	$ 3,513
Construction Mortgages | Arlington
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Contractual Interest Rate	8.00%
Prior Liens				0
Principal Balance	$ 1,056			1,056
Book Value				$ 1,078
Deductions during period:
Balance at the end of the year	$ 1,056