Segment Reporting Footnote Tagging (Details)	9 Months Ended
	Sep. 30, 2017 Property Unit Integer Segment	Jan. 31, 2016 Security
Segment Reporting Information [Line Items]
Number of Reportable Segments | Segment	4
Commercial Real Estate [Member]
Segment Reporting Information [Line Items]
Number of collateralized securities | Integer	1
Tax-exempt and Other Investments [Member]
Segment Reporting Information [Line Items]
Assets percentage	25.00%
MBS Securities Investments [Member]
Segment Reporting Information [Line Items]
Number of partnership securities sold and eliminated. | Security		3
Mortgage Revenue Bond Investments Segment [Member]
Segment Reporting Information [Line Items]
Number of Available for Sale Securities | Integer	91
Mortgage Revenue Bond Investments Segment [Member] | Residential Properties [Member]
Segment Reporting Information [Line Items]
Units | Unit	10,788
Real Estate [Member]
Segment Reporting Information [Line Items]
Units | Unit	1,710
Number of Real Estate Properties | Property	6