Variable Interest Entities Consolidating Balance Sheet (Details) (USD $)	Feb. 28, 2013	Dec. 31, 2012	Sep. 30, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Assets [Abstract]
Cash and cash equivalents		$ 30,172,773		$ 20,086,841
Restricted cash		5,471,522		12,904,361
Interest receivable		8,473,360		6,984,978
Tax-exempt mortgage revenue bonds held in trust, at fair value		99,534,082		109,152,787
Tax-exempt mortgage revenue bonds, at fair value		45,703,294	45,703,294	26,542,565
Public housing capital fund trusts, at fair value		65,389,298		0
Mortgage backed securities, at fair value		32,121,412		0
Real Estate Assets [Abstract]
Land		11,202,876		8,313,160
Buildings and improvements		93,615,479		82,261,705
Real estate assets before accumulated depreciation		104,818,355		90,574,865
Accumulated depreciation		(19,330,063)		(15,305,931)
Net real estate assets		85,488,292		75,268,934
Other Assets		8,216,295		9,541,379
Assets of discontinued operations		32,580,427		37,494,700
Assets		413,150,755		297,976,545	241,607,249
Liabilities
Accounts payable, accrued expenses and other liabilities		5,013,947		2,465,785
Distribution payable		5,566,908		3,911,340
Debt financing		177,948,000		112,673,000
Mortgages payable	7,500,000	39,119,507		35,464,455
Liabilities of discontinued operations		1,531,462		11,872,920
Liabilities		229,179,824		166,387,500
General Partner		(430,087)		(354,006)
Beneficial Unit Certificate holders		207,383,087		154,911,228
Unallocated deficit of Consolidated VIEs		(25,035,808)		(23,512,962)
Total Partners' Capital		181,917,192		131,044,260	128,162,891
Noncontrolling interest		2,053,739		544,785
Total Capital		183,970,931		131,589,045	128,021,565	98,600,740
Total Liabilities and Partners' Capital		413,150,755		297,976,545
Partnership [Member]
Assets [Abstract]
Cash and cash equivalents		30,123,447		20,074,123
Restricted cash		4,538,071		11,967,308
Interest receivable		14,131,063		11,395,266
Tax-exempt mortgage revenue bonds held in trust, at fair value		124,149,600		132,920,723
Tax-exempt mortgage revenue bonds, at fair value		45,703,294		26,542,565
Public housing capital fund trusts, at fair value		65,389,298
Mortgage backed securities, at fair value		32,121,412
Real Estate Assets [Abstract]
Land		6,798,407		5,063,116
Buildings and improvements		55,776,753		50,653,712
Real estate assets before accumulated depreciation		62,575,160		55,716,828
Accumulated depreciation		(5,458,961)		(2,973,597)
Net real estate assets		57,116,199		52,743,231
Other Assets		22,923,356		19,552,919
Assets of discontinued operations		32,580,427		37,494,700
Assets		428,776,167		312,690,835
Liabilities
Accounts payable, accrued expenses and other liabilities		2,330,852		1,490,994
Distribution payable		5,566,908		3,911,340
Debt financing		177,948,000		112,673,000
Mortgages payable		39,119,507		35,464,455
Liabilities of discontinued operations		1,531,462		11,872,920
Liabilities		226,496,729		165,412,709
General Partner		(430,087)		(354,006)
Beneficial Unit Certificate holders		200,655,786		147,087,347
Unallocated deficit of Consolidated VIEs		0		0
Total Partners' Capital		200,225,699		146,733,341
Noncontrolling interest		2,053,739		544,785
Total Capital		202,279,438		147,278,126
Total Liabilities and Partners' Capital		428,776,167		312,690,835
Consolidated VIEs [Member]
Assets [Abstract]
Cash and cash equivalents		49,326		12,718
Restricted cash		933,451		937,053
Interest receivable		0		0
Tax-exempt mortgage revenue bonds held in trust, at fair value		0		0
Tax-exempt mortgage revenue bonds, at fair value		0		0
Public housing capital fund trusts, at fair value		0
Mortgage backed securities, at fair value		0
Real Estate Assets [Abstract]
Land		4,404,469		3,250,044
Buildings and improvements		37,838,726		31,607,993
Real estate assets before accumulated depreciation		42,243,195		34,858,037
Accumulated depreciation		(13,871,102)		(12,332,334)
Net real estate assets		28,372,093		22,525,703
Other Assets		852,321		839,879
Assets of discontinued operations		0		0
Assets		30,207,191		24,315,353	47,504,227
Liabilities
Accounts payable, accrued expenses and other liabilities		28,529,405		24,780,781
Distribution payable		0		0
Debt financing		0		0
Mortgages payable		24,158,000		24,407,000
Liabilities of discontinued operations		0		0
Liabilities		52,687,405		49,187,781
General Partner		0		0
Beneficial Unit Certificate holders		0		0
Unallocated deficit of Consolidated VIEs		(22,480,214)		(24,872,428)
Total Partners' Capital		(22,480,214)		(24,872,428)	(41,635,836)
Noncontrolling interest		0		0
Total Capital		(22,480,214)		(24,872,428)
Total Liabilities and Partners' Capital		30,207,191		24,315,353
Consolidations, Eliminations for VIEs [Member]
Assets [Abstract]
Cash and cash equivalents		0		0
Restricted cash		0		0
Interest receivable		(5,657,703)		(4,410,288)
Tax-exempt mortgage revenue bonds held in trust, at fair value		(24,615,518)		(23,767,936)
Tax-exempt mortgage revenue bonds, at fair value		0		0
Public housing capital fund trusts, at fair value		0
Mortgage backed securities, at fair value		0
Real Estate Assets [Abstract]
Land		0		0
Buildings and improvements		0		0
Real estate assets before accumulated depreciation		0		0
Accumulated depreciation		0		0
Net real estate assets		0		0
Other Assets		(15,559,382)		(10,851,419)
Assets of discontinued operations		0		0
Assets		(45,832,603)		(39,029,643)
Liabilities
Accounts payable, accrued expenses and other liabilities		(25,846,310)		(23,805,990)
Distribution payable		0		0
Debt financing		0		0
Mortgages payable		(24,158,000)		(24,407,000)
Liabilities of discontinued operations		0		0
Liabilities		(50,004,310)		(48,212,990)
General Partner		0		0
Beneficial Unit Certificate holders		6,727,301		7,823,881
Unallocated deficit of Consolidated VIEs		(2,555,594)		1,359,466
Total Partners' Capital		4,171,707		9,183,347
Noncontrolling interest		0		0
Total Capital		4,171,707		9,183,347
Total Liabilities and Partners' Capital		$ (45,832,603)		$ (39,029,643)