Real Estate Debt Investments - Narrative (Details)	6 Months Ended	12 Months Ended
	Jun. 30, 2019 Investment sub_portfolio	Dec. 31, 2018 Investment
Real Estate [Line Items]
Number of debt instruments | Investment	1	1
Number of days past contractual debt service payments loan categorized as a weaker credit quality debt investment	90 days
Percent of interest income contributed by investment	100.00%
Espresso
Real Estate [Line Items]
Number of sub-portfolios containing a tenant lease in default | sub_portfolio	1