Segment Reporting - Narrative (Details) ft² in Millions	9 Months Ended
	Sep. 30, 2017 ft² security state segment loan property	Dec. 31, 2016 security
Segment Reporting Information [Line Items]
Number of operating segments | segment	2
Number of loans held for investment | loan	8
Commercial Mortgage Backed Securities [Member]
Segment Reporting Information [Line Items]
Number of securities held | security	8	8
REI Segment [Member] | Consolidated Properties [Member]
Segment Reporting Information [Line Items]
Number of properties owned | property	4,094
Square feet of property | ft²	92.5
Number of states in which entity operates | state	49
Percentage of rentable space leased	98.70%
Real estate property, weighted average remaining lease term	9 years 5 months 27 days