Segment Reporting Footnote Tagging (Details)	9 Months Ended
	Sep. 30, 2015 properties Integer Unit entities
Segment Reporting Information [Line Items]
Number of Available for Sale Securities | Integer	53
Number of Variable Interest Entities	13
Mortgage revenue bonds [Member]
Segment Reporting Information [Line Items]
Number of Units in Real Estate Property | Unit	7,332
MF Properties [Member]
Segment Reporting Information [Line Items]
Number of Units in Real Estate Property | Unit	2,216
Number of Real Estate Properties	6
Consolidated VIEs [Member]
Segment Reporting Information [Line Items]
Number of Variable Interest Entities	2
Public housing capital fund trusts [Member]
Segment Reporting Information [Line Items]
Number of Available for Sale Securities, Public Housing Authorities | Integer	3
Unconsolidated Available for Sale Securities [Member]
Segment Reporting Information [Line Items]
Number of Available for Sale Securities | Integer	59
Consolidated VIEs [Member]
Segment Reporting Information [Line Items]
Number of Available for Sale Securities | Integer	2
Consolidated Properties [Member]
Segment Reporting Information [Line Items]
Number of Real Estate Properties	8
Consolidated Properties [Member] | MF Properties [Member]
Segment Reporting Information [Line Items]
Number of Real Estate Properties | entities	8