Segment Reporting - Narrative (Details)	12 Months Ended
	Dec. 31, 2014 security	Dec. 31, 2013 security
Segment Reporting Information [Line Items]
Number of reportable segments	2
Commercial Mortgage Backed Securities [Member]
Segment Reporting Information [Line Items]
Number of securities acquired	10	10
Real Estate Investment Segment [Member]
Segment Reporting Information [Line Items]
Number of loans held for investment	14
Real Estate Investment Segment [Member] | Commercial Mortgage Backed Securities [Member]
Segment Reporting Information [Line Items]
Number of securities acquired	10
Real Estate Investment Segment [Member] | Consolidated Properties [Member]
Segment Reporting Information [Line Items]
Number of owned properties	4,648
Square feet of property	103,100,000
Number of states in which entity operates	49
Percentage of rentable space leased	99.30%
Real estate property, weighted average remaining lease term	11 years 9 months 18 days
Real Estate Investment Segment [Member] | Unconsolidated Properties [Member]
Segment Reporting Information [Line Items]
Net rentable area (in square feet)	1,600,000
Unconsolidated Joint Venture [Member]
Segment Reporting Information [Line Items]
Number of owned properties	6