Real Estate Investments - Mortgage Loans (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2016 USD ($) loan	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Mortgage Loans
Scheduled principal payments received	$ 8,278	$ 4,808	$ 9,155
Carrying value of mortgage loans	$ 229,801	217,529
Minimum
Mortgage Loans
General amortization schedule of mortgage loans	20 years
Maximum
Mortgage Loans
General amortization schedule of mortgage loans	30 years
Mortgage Loans on Real Estate
Mortgage Loans
Origination/Funding	$ 20,685	67,134
Payoffs	6,036	2,487
Scheduled principal payments received	2,242	2,321	$ 2,159
Carrying value of mortgage loans	229,801	$ 217,529
Scheduled principal payments on mortgage loan receivables
2017	7,674
2018	8,297
2019	5,092
2020	8,815
2021	1,065
Thereafter	201,173
Total	$ 232,116
Mortgage Loans on Real Estate | Missouri, Texas and Washington
Mortgage Loans
Number of Loans | loan	9
Mortgage Loans on Real Estate | Minimum
Mortgage Loans
Interest rate for mortgage loan (as a percent)	7.30%
General amortization schedule of mortgage loans	20 years
Specified basis points for annual increase in interest rate (as a percent)	0.10%
Mortgage Loans on Real Estate | Maximum
Mortgage Loans
Interest rate for mortgage loan (as a percent)	13.90%
General amortization schedule of mortgage loans	30 years
Specified basis points for annual increase in interest rate (as a percent)	0.25%