Schedule IV - Mortgage Loans on Real Estate (Details)	12 Months Ended
	Dec. 31, 2018 USD ($)
Mortgage Loans on Real Estate
Prior Liens	$ 11,367,000
Face Amount of Mortgages	440,583,000
Carrying Amount of Mortgages	249,071,000
Principal Amount of Loans Subject to Delinquent Principal or Interest	$ 0
First mortgage loans | Triple-net | California
Mortgage Loans on Real Estate
Interest Rate	8.11%
Periodic Payment Amount	$ 0
Prior Liens	0
Face Amount of Mortgages	28,000,000
Carrying Amount of Mortgages	9,247,000
Principal Amount of Loans Subject to Delinquent Principal or Interest	$ 0
First mortgage loans | Triple-net | California
Mortgage Loans on Real Estate
Interest Rate	7.95%
Periodic Payment Amount	$ 1,000
Prior Liens	0
Face Amount of Mortgages	131,100,000
Carrying Amount of Mortgages	53,172,000
Principal Amount of Loans Subject to Delinquent Principal or Interest	$ 0
First mortgage loans | Triple-net | United Kingdom
Mortgage Loans on Real Estate
Interest Rate	8.54%
Periodic Payment Amount	$ 0
Prior Liens	0
Face Amount of Mortgages	2,678,000
Carrying Amount of Mortgages	1,284,000
Principal Amount of Loans Subject to Delinquent Principal or Interest	$ 0
First mortgage loans | Triple-net | United Kingdom
Mortgage Loans on Real Estate
Interest Rate	8.00%
Periodic Payment Amount	$ 0
Prior Liens	0
Face Amount of Mortgages	11,041,000
Carrying Amount of Mortgages	6,638,000
Principal Amount of Loans Subject to Delinquent Principal or Interest	$ 0
First mortgage loans | Triple-net | United Kingdom
Mortgage Loans on Real Estate
Interest Rate	8.55%
Periodic Payment Amount	$ 0
Prior Liens	0
Face Amount of Mortgages	14,600,000
Carrying Amount of Mortgages	14,599,000
Principal Amount of Loans Subject to Delinquent Principal or Interest	$ 0
First mortgage loans | Triple-net | United Kingdom
Mortgage Loans on Real Estate
Interest Rate	7.00%
Periodic Payment Amount	$ 0
Prior Liens	0
Face Amount of Mortgages	26,748,000
Carrying Amount of Mortgages	20,283,000
Principal Amount of Loans Subject to Delinquent Principal or Interest	$ 0
First mortgage loans | Triple-net | United Kingdom
Mortgage Loans on Real Estate
Interest Rate	8.28%
Periodic Payment Amount	$ 0
Prior Liens	0
Face Amount of Mortgages	19,131,000
Carrying Amount of Mortgages	19,131,000
Principal Amount of Loans Subject to Delinquent Principal or Interest	$ 0
First mortgage loans | Triple-net | Oklahoma
Mortgage Loans on Real Estate
Interest Rate	9.32%
Periodic Payment Amount	$ 0
Prior Liens	0
Face Amount of Mortgages	11,610,000
Carrying Amount of Mortgages	11,595,000
Principal Amount of Loans Subject to Delinquent Principal or Interest	$ 0
First mortgage loans | Triple-net | Pennsylvania
Mortgage Loans on Real Estate
Interest Rate	8.47%
Periodic Payment Amount	$ 0
Prior Liens	0
Face Amount of Mortgages	15,530,000
Carrying Amount of Mortgages	14,237,000
Principal Amount of Loans Subject to Delinquent Principal or Interest	$ 0
First mortgage loans | Triple-net | Florida
Mortgage Loans on Real Estate
Interest Rate	10.20%
Periodic Payment Amount	$ 0
Prior Liens	0
Face Amount of Mortgages	17,100,000
Carrying Amount of Mortgages	17,385,000
Principal Amount of Loans Subject to Delinquent Principal or Interest	$ 0
First mortgage loans | Triple-net | North Carolina
Mortgage Loans on Real Estate
Interest Rate	7.60%
Periodic Payment Amount	$ 0
Prior Liens	0
Face Amount of Mortgages	30,883,000
Carrying Amount of Mortgages	3,000,000
Principal Amount of Loans Subject to Delinquent Principal or Interest	$ 0
First mortgage loans | Triple-net | United Kingdom
Mortgage Loans on Real Estate
Interest Rate	8.50%
Periodic Payment Amount	$ 0
Prior Liens	0
Face Amount of Mortgages	19,104,000
Carrying Amount of Mortgages	6,505,000
Principal Amount of Loans Subject to Delinquent Principal or Interest	$ 0
First mortgage loans | Triple-net | 4 properties in Texas
Mortgage Loans on Real Estate
Interest Rate	7.95%
Periodic Payment Amount	$ 1,000
Prior Liens	0
Face Amount of Mortgages	106,218,000
Carrying Amount of Mortgages	65,162,000
Principal Amount of Loans Subject to Delinquent Principal or Interest
First mortgage loans | Outpatient Medical | Texas
Mortgage Loans on Real Estate
Interest Rate	7.60%
Periodic Payment Amount	$ 0
Prior Liens	0
Face Amount of Mortgages	3,740,000
Carrying Amount of Mortgages	3,733,000
Principal Amount of Loans Subject to Delinquent Principal or Interest	$ 0
Second mortgage loans | Triple-net | Texas
Mortgage Loans on Real Estate
Interest Rate	12.17%
Periodic Payment Amount	$ 0
Prior Liens	11,367,000
Face Amount of Mortgages	3,100,000
Carrying Amount of Mortgages	3,100,000
Principal Amount of Loans Subject to Delinquent Principal or Interest