Investments in Mortgage Revenue Bonds Acquisitions (Details)		1 Months Ended					12 Months Ended
		Aug. 31, 2016 USD ($) Unit	May 31, 2016 USD ($) Unit	Mar. 31, 2016 USD ($)	Jul. 31, 2015 USD ($) Unit	Jun. 30, 2015 USD ($) Unit	Dec. 31, 2016 USD ($) Unit		Dec. 31, 2015 USD ($) Unit		Oct. 31, 2015 Unit
Schedule Of Available For Sale Securities [Line Items]
Units | Unit											2
Principal Outstanding							$ 648,439,860		$ 534,745,500
Pro Nova 2014B [Member]
Schedule Of Available For Sale Securities [Line Items]
Original Maturity Date	[1]			May 01, 2025
Base Interest Rate	[1]			5.25%
Principal Outstanding	[1]			$ 9,295,000
Companion At Thornhill Apts [Member]
Schedule Of Available For Sale Securities [Line Items]
Units | Unit							178
Original Maturity Date	[2]						Jan. 01, 2052
Base Interest Rate	[2]						5.80%
Principal Outstanding	[2]						$ 11,500,000
15 West Apartments [Member]
Schedule Of Available For Sale Securities [Line Items]
Units | Unit	[3]						120
Original Maturity Date	[3]						Jul. 01, 2054
Base Interest Rate	[3]						6.25%
Principal Outstanding	[3]						$ 9,850,000
Vantage at Harlingen [Member]
Schedule Of Available For Sale Securities [Line Items]
Units | Unit									288
Original Maturity Date	[4]						Sep. 01, 2053		Sep. 01, 2053
Base Interest Rate	[4]						6.00%		9.00%
Principal Outstanding	[4]						$ 24,529,580		$ 24,575,000
Vantage at Judson [Member]
Schedule Of Available For Sale Securities [Line Items]
Units | Unit									288
Original Maturity Date	[4]						Jan. 01, 2053		Jan. 01, 2053
Base Interest Rate	[4]						6.00%		9.00%
Principal Outstanding	[4]						$ 26,356,498		$ 26,540,000
Rennaisance [Member]
Schedule Of Available For Sale Securities [Line Items]
Units | Unit						208
Original Maturity Date						Jun. 01, 2050
Base Interest Rate						6.00%
Principal Outstanding						$ 11,500,000
The Suites on Paseo [Member]
Schedule Of Available For Sale Securities [Line Items]
Units | Unit							394		394
Columbia Gardens [Member]
Schedule Of Available For Sale Securities [Line Items]
Units | Unit									188
Original Maturity Date							Dec. 01, 2050	[2]	Dec. 01, 2050	[5]
Base Interest Rate							5.50%	[2]	5.50%	[5]
Principal Outstanding							$ 15,000,000	[2]	$ 15,000,000	[5]
Willow Run [Member]
Schedule Of Available For Sale Securities [Line Items]
Units | Unit									200
Original Maturity Date							Dec. 01, 2050	[2]	Dec. 01, 2050	[5]
Base Interest Rate							5.50%	[2]	5.50%	[5]
Principal Outstanding							$ 15,000,000	[2]	$ 15,000,000	[5]
Series B [Member] | Glenview Apartments [Member]
Schedule Of Available For Sale Securities [Line Items]
Units | Unit			88
Original Maturity Date			Dec. 01, 2016						Dec. 01, 2016
Base Interest Rate			8.00%						8.00%
Principal Outstanding			$ 2,053,000						$ 2,053,000
Series B [Member] | Montclair Apartments [Member]
Schedule Of Available For Sale Securities [Line Items]
Units | Unit			80
Original Maturity Date			Dec. 01, 2016
Base Interest Rate			8.00%
Principal Outstanding			$ 928,000
Series B [Member] | Santa Fe Apartments [Member]
Schedule Of Available For Sale Securities [Line Items]
Units | Unit			89
Original Maturity Date			Dec. 01, 2016
Base Interest Rate			8.00%
Principal Outstanding			$ 1,671,000
Series B [Member] | Heritage Square [Member]
Schedule Of Available For Sale Securities [Line Items]
Units | Unit			204
Original Maturity Date			Oct. 01, 2051						Oct. 01, 2051
Base Interest Rate			12.00%						12.00%
Principal Outstanding			$ 520,000						$ 520,000
Series B [Member] | Concord at Gulfgate [Member]
Schedule Of Available For Sale Securities [Line Items]
Units | Unit		288							288
Original Maturity Date		Mar. 01, 2032							Mar. 01, 2032
Base Interest Rate		12.00%							12.00%
Principal Outstanding		$ 2,125,000							$ 2,125,000
Series B [Member] | Concord at Little York [Member]
Schedule Of Available For Sale Securities [Line Items]
Units | Unit		276							276
Original Maturity Date		Mar. 01, 2032							Mar. 01, 2032
Base Interest Rate		12.00%							12.00%
Principal Outstanding		$ 960,000							$ 960,000
Series B [Member] | Concord at Williamcrest [Member]
Schedule Of Available For Sale Securities [Line Items]
Units | Unit		288							288
Original Maturity Date		Mar. 01, 2032							Mar. 01, 2032
Base Interest Rate		12.00%							12.00%
Principal Outstanding		$ 2,800,000							$ 2,800,000
Series B [Member] | Las Palmas II [Member]
Schedule Of Available For Sale Securities [Line Items]
Units | Unit							81
Original Maturity Date							Nov. 01, 2018
Base Interest Rate							5.50%
Principal Outstanding							$ 1,770,000
Series B [Member] | San Vicente [Member]
Schedule Of Available For Sale Securities [Line Items]
Units | Unit							50
Original Maturity Date							Nov. 01, 2018
Base Interest Rate							5.50%
Principal Outstanding							$ 1,825,000
Series B [Member] | Harmony Court Bakersfield [Member]
Schedule Of Available For Sale Securities [Line Items]
Units | Unit							96
Original Maturity Date							Dec. 01, 2018
Base Interest Rate							5.50%
Principal Outstanding							$ 1,997,000
Series B [Member] | Summerhill [Member]
Schedule Of Available For Sale Securities [Line Items]
Units | Unit							128
Original Maturity Date							Dec. 01, 2018
Base Interest Rate							5.50%
Principal Outstanding							$ 3,372,000
Series B [Member] | The Village at Madera [Member]
Schedule Of Available For Sale Securities [Line Items]
Units | Unit							75
Original Maturity Date							Dec. 01, 2018
Base Interest Rate							5.50%
Principal Outstanding							$ 1,719,000
Series B [Member] | Courtyard Apartments [Member]
Schedule Of Available For Sale Securities [Line Items]
Units | Unit							108
Original Maturity Date							Dec. 01, 2018
Base Interest Rate							5.50%
Principal Outstanding							$ 6,228,000
Series B [Member] | Harmony Terrace [Member]
Schedule Of Available For Sale Securities [Line Items]
Units | Unit							136
Original Maturity Date	[2]						Jan. 01, 2019
Base Interest Rate	[2]						5.50%
Principal Outstanding	[2]						$ 7,400,000
Series B [Member] | Oaks at Georgetown [Member]
Schedule Of Available For Sale Securities [Line Items]
Units | Unit							192
Original Maturity Date	[2]						Jan. 01, 2019
Base Interest Rate	[2]						5.50%
Principal Outstanding	[2]						$ 5,512,000
Series B [Member] | Seasons Lakewood [Member]
Schedule Of Available For Sale Securities [Line Items]
Units | Unit							85
Original Maturity Date							Jan. 01, 2019
Base Interest Rate							5.50%
Principal Outstanding							$ 5,260,000
Series B [Member] | Seasons San Juan Capistrano [Member]
Schedule Of Available For Sale Securities [Line Items]
Units | Unit							112
Original Maturity Date							Jan. 01, 2019
Base Interest Rate							5.50%
Principal Outstanding							$ 6,574,000
Series B [Member] | Harden Ranch [Member]
Schedule Of Available For Sale Securities [Line Items]
Units | Unit					100
Original Maturity Date					Mar. 01, 2016
Base Interest Rate					8.00%
Principal Outstanding					$ 2,340,000
Series B [Member] | Tyler Park [Member]
Schedule Of Available For Sale Securities [Line Items]
Units | Unit					88
Original Maturity Date					Jan. 01, 2016
Base Interest Rate					8.00%
Principal Outstanding					$ 2,025,000
Series B [Member] | Westside Village [Member]
Schedule Of Available For Sale Securities [Line Items]
Units | Unit					81
Original Maturity Date					Jan. 01, 2016
Base Interest Rate					8.00%
Principal Outstanding					$ 1,430,000
Series B [Member] | The Suites on Paseo [Member]
Schedule Of Available For Sale Securities [Line Items]
Units | Unit									394
Original Maturity Date									Dec. 01, 2033
Base Interest Rate									9.00%
Principal Outstanding									$ 5,500,000
Series B [Member] | Avistar at the Parkway [Member]
Schedule Of Available For Sale Securities [Line Items]
Units | Unit									236
Original Maturity Date							Jun. 01, 2052		Jun. 01, 2052
Base Interest Rate							12.00%		12.00%
Principal Outstanding							$ 125,000		$ 125,000
Series B [Member] | Silver Moon [Member]
Schedule Of Available For Sale Securities [Line Items]
Principal Outstanding							$ 500,000
Series B [Member] | Seasons at Simi Valley [Member]
Schedule Of Available For Sale Securities [Line Items]
Units | Unit									69
Original Maturity Date							Sep. 01, 2017		Sep. 01, 2017
Base Interest Rate							8.00%		5.50%
Principal Outstanding							$ 1,944,000		$ 1,944,000
Series B [Member] | Crossing at 1415 [Member]
Schedule Of Available For Sale Securities [Line Items]
Units | Unit									112
Original Maturity Date							Jan. 01, 2053		Jan. 01, 2053
Base Interest Rate							12.00%		12.00%
Principal Outstanding							$ 335,000		$ 335,000
Series B [Member] | Heights at 515 [Member]
Schedule Of Available For Sale Securities [Line Items]
Units | Unit									97
Original Maturity Date							Jan. 01, 2053		Jan. 01, 2053
Base Interest Rate							12.00%		12.00%
Principal Outstanding							$ 510,000		$ 510,000
Series B [Member] | Sycamore Walk [Member]
Schedule Of Available For Sale Securities [Line Items]
Units | Unit									112
Original Maturity Date							Jan. 01, 2018		Jan. 01, 2018
Base Interest Rate							5.50%		5.50%
Principal Outstanding							$ 1,815,000		$ 1,815,000
Series A [Member] | Glenview Apartments [Member]
Schedule Of Available For Sale Securities [Line Items]
Original Maturity Date	[4]						Dec. 01, 2031		Dec. 01, 2031
Base Interest Rate	[4]						5.75%		5.75%
Principal Outstanding	[4]						$ 4,670,000		$ 4,670,000
Series A [Member] | Heritage Square [Member]
Schedule Of Available For Sale Securities [Line Items]
Original Maturity Date	[4]						Sep. 01, 2051		Sep. 01, 2051
Base Interest Rate	[4]						6.00%		6.00%
Principal Outstanding	[4]						$ 11,161,330		$ 11,185,000
Series A [Member] | Concord at Gulfgate [Member]
Schedule Of Available For Sale Securities [Line Items]
Units | Unit									288
Original Maturity Date							Feb. 01, 2032	[2]	Feb. 01, 2032	[5]
Base Interest Rate							6.00%	[2]	6.00%	[5]
Principal Outstanding							$ 19,185,000	[2]	$ 17,060,000	[5]
Series A [Member] | Concord at Little York [Member]
Schedule Of Available For Sale Securities [Line Items]
Units | Unit									276
Original Maturity Date							Feb. 01, 2032	[2]	Feb. 01, 2032	[5]
Base Interest Rate							6.00%	[2]	6.00%	[5]
Principal Outstanding							$ 13,440,000	[2]	$ 12,480,000	[5]
Series A [Member] | Concord at Williamcrest [Member]
Schedule Of Available For Sale Securities [Line Items]
Units | Unit									288
Original Maturity Date							Feb. 01, 2032	[2]	Feb. 01, 2032	[5]
Base Interest Rate							6.00%	[2]	6.00%	[5]
Principal Outstanding							$ 20,820,000	[2]	$ 18,020,000	[5]
Series A [Member] | Las Palmas II [Member]
Schedule Of Available For Sale Securities [Line Items]
Units | Unit							81
Original Maturity Date							Nov. 01, 2033
Base Interest Rate							5.00%
Principal Outstanding							$ 1,695,000
Series A [Member] | San Vicente [Member]
Schedule Of Available For Sale Securities [Line Items]
Units | Unit							50
Original Maturity Date							Nov. 01, 2033
Base Interest Rate							5.00%
Principal Outstanding							$ 3,495,000
Series A [Member] | Harmony Court Bakersfield [Member]
Schedule Of Available For Sale Securities [Line Items]
Units | Unit							96
Original Maturity Date							Dec. 01, 2033
Base Interest Rate							5.00%
Principal Outstanding							$ 3,730,000
Series A [Member] | Summerhill [Member]
Schedule Of Available For Sale Securities [Line Items]
Units | Unit							128
Original Maturity Date							Dec. 01, 2033
Base Interest Rate							5.00%
Principal Outstanding							$ 6,423,000
Series A [Member] | The Village at Madera [Member]
Schedule Of Available For Sale Securities [Line Items]
Units | Unit							75
Original Maturity Date							Dec. 01, 2033
Base Interest Rate							5.00%
Principal Outstanding							$ 3,085,000
Series A [Member] | 15 West Apartments [Member]
Schedule Of Available For Sale Securities [Line Items]
Original Maturity Date	[2]						Jul. 01, 2054
Base Interest Rate	[2]						6.25%
Principal Outstanding	[2]						$ 9,850,000
Series A [Member] | Courtyard Apartments [Member]
Schedule Of Available For Sale Securities [Line Items]
Units | Unit							108
Original Maturity Date							Dec. 01, 2033
Base Interest Rate							5.00%
Principal Outstanding							$ 10,230,000
Series A [Member] | Harmony Terrace [Member]
Schedule Of Available For Sale Securities [Line Items]
Units | Unit							136
Original Maturity Date	[2]						Jan. 01, 2034
Base Interest Rate	[2]						5.00%
Principal Outstanding	[2]						$ 6,900,000
Series A [Member] | Oaks at Georgetown [Member]
Schedule Of Available For Sale Securities [Line Items]
Units | Unit							192
Original Maturity Date	[2]						Jan. 01, 2034
Base Interest Rate	[2]						5.00%
Principal Outstanding	[2]						$ 12,330,000
Series A [Member] | Seasons Lakewood [Member]
Schedule Of Available For Sale Securities [Line Items]
Units | Unit							85
Original Maturity Date							Jan. 01, 2034
Base Interest Rate							5.00%
Principal Outstanding							$ 7,350,000
Series A [Member] | Seasons San Juan Capistrano [Member]
Schedule Of Available For Sale Securities [Line Items]
Units | Unit							112
Original Maturity Date							Jan. 01, 2034
Base Interest Rate							5.00%
Principal Outstanding							$ 12,375,000
Series A [Member] | Harden Ranch [Member]
Schedule Of Available For Sale Securities [Line Items]
Original Maturity Date							Mar. 01, 2030	[6]	Mar. 01, 2030	[7]
Base Interest Rate							5.75%	[6]	5.75%	[7]
Principal Outstanding							$ 6,912,535	[6]	$ 6,960,000	[7]
Series A [Member] | Rennaisance [Member]
Schedule Of Available For Sale Securities [Line Items]
Original Maturity Date	[4]						Jun. 01, 2050		Jun. 01, 2050
Base Interest Rate	[4]						6.00%		6.00%
Principal Outstanding	[4]						$ 11,348,364		$ 11,450,959
Series A [Member] | Avistar at the Parkway [Member]
Schedule Of Available For Sale Securities [Line Items]
Units | Unit									236
Original Maturity Date	[4]						May 01, 2052		May 01, 2052
Base Interest Rate	[4]						6.00%		6.00%
Principal Outstanding	[4]						$ 13,300,000		$ 13,300,000
Series A [Member] | Silver Moon [Member]
Schedule Of Available For Sale Securities [Line Items]
Units | Unit									151
Original Maturity Date	[4]						Aug. 01, 2055		Aug. 01, 2055
Base Interest Rate	[4]						6.00%		6.00%
Principal Outstanding	[4]						$ 7,933,259		$ 7,983,811
Series A [Member] | Seasons at Simi Valley [Member]
Schedule Of Available For Sale Securities [Line Items]
Units | Unit									69
Original Maturity Date							Sep. 01, 2032	[2]	Sep. 01, 2032
Base Interest Rate							5.75%	[2]	5.75%
Principal Outstanding							$ 4,376,000	[2]	$ 4,376,000
Series A [Member] | Crossing at 1415 [Member]
Schedule Of Available For Sale Securities [Line Items]
Units | Unit									112
Original Maturity Date							Dec. 01, 2052	[2]	Dec. 01, 2052
Base Interest Rate							6.00%	[2]	6.00%
Principal Outstanding							$ 7,590,000	[2]	$ 7,590,000
Series A [Member] | Heights at 515 [Member]
Schedule Of Available For Sale Securities [Line Items]
Units | Unit									97
Original Maturity Date							Dec. 01, 2052	[2]	Dec. 01, 2052
Base Interest Rate							6.00%	[2]	6.00%
Principal Outstanding							$ 6,435,000	[2]	$ 6,435,000
Series A [Member] | Sycamore Walk [Member]
Schedule Of Available For Sale Securities [Line Items]
Units | Unit									112
Original Maturity Date							Jan. 01, 2033	[2]	Jan. 01, 2033
Base Interest Rate							5.25%	[2]	5.25%
Principal Outstanding							$ 3,632,000	[2]	$ 3,632,000
Series C [Member] | Vantage at Harlingen [Member]
Schedule Of Available For Sale Securities [Line Items]
Units | Unit						288
Original Maturity Date						Oct. 01, 2053
Base Interest Rate						9.00%
Principal Outstanding						$ 6,692,000
Series C [Member] | Vantage at Judson [Member]
Schedule Of Available For Sale Securities [Line Items]
Units | Unit						288
Original Maturity Date						Feb. 01, 2053
Base Interest Rate						9.00%
Principal Outstanding						$ 6,049,000

[1] This is a commercial property. Accordingly, unit information is not applicable.

[2] Bond held by Deutsche Bank AG in a secured financing transaction, see Note 17

[3] Previously reported Bond Purchase Commitment that converted to a mortgage revenue bond in December 2016.

[4] Bonds owned by ATAX TEBS III, LLC (M33 TEBS), see Note 17

[5] Bonds held by Deutsche Bank AG in a secured financing transaction, see Note 17

[6] Bonds owned by ATAX TEBS II, LLC (M31 TEBS), see Note 17

[7] Bonds held by ATAX TEBS II, LLC (M31 TEBS), see Note 17