Segments - Additional Information (Details)	9 Months Ended
	Sep. 30, 2019 Property Unit Security Segment Rating
Segment Reporting Information [Line Items]
Number of Reportable Segments | Segment	4
Mortgage Revenue Bond Investments Segment [Member]
Segment Reporting Information [Line Items]
Number of Available for Sale Securities | Security	76
Real Estate [Member]
Segment Reporting Information [Line Items]
Number of Real Estate Properties | Property	2
Number of rental units under MF properties segment. | Unit	859
Residential Properties [Member] | Mortgage Revenue Bond Investments Segment [Member]
Segment Reporting Information [Line Items]
Number of rental units financed by mortgage revenue bonds | Unit	10,871
Commercial Real Estate [Member] | Mortgage Revenue Bond Investments Segment [Member]
Segment Reporting Information [Line Items]
Number of collateralized securities | Security	1
Minimum [Member]
Segment Reporting Information [Line Items]
Required rating for tax exempted investments other than mortgage revenue bonds | Rating	1
Maximum [Member]
Segment Reporting Information [Line Items]
Required rating for tax exempted investments other than mortgage revenue bonds | Rating	4
Tax-exempt Securities Other Than MRBs and Other Investments [Member]
Segment Reporting Information [Line Items]
Assets percentage	25.00%