INVESTMENTS IN OPERATING PARTNERSHIPS - Financial Results (Details) - USD ($)	6 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Revenues
Rental	$ 2,019,266	$ 3,039,627
Interest and other	31,102	60,035
Operating Partnerships Revenue	2,050,368	3,099,662
Expenses
Interest	281,723	347,505
Depreciation and amortization	485,006	742,101
Operating expenses	1,634,700	2,477,569
Operating Partnerships Total Expenses	2,401,429	3,567,175
NET LOSS	(351,061)	(467,513)
Net loss allocation to Boston Capital Tax Credit Fund III L.P.	(347,549)	(462,837)
Net loss allocated to other Partners	(3,512)	(4,676)
Series 15
Revenues
Rental	0	502,625
Interest and other	0	10,626
Operating Partnerships Revenue	0	513,251
Expenses
Interest	0	36,618
Depreciation and amortization	0	122,439
Operating expenses	0	424,667
Operating Partnerships Total Expenses	0	583,724
NET LOSS	0	(70,473)
Net loss allocation to Boston Capital Tax Credit Fund III L.P.	0	(69,768)
Net loss allocated to other Partners	0	(705)
Series 16
Revenues
Rental	922,631	1,062,557
Interest and other	9,347	12,948
Operating Partnerships Revenue	931,978	1,075,505
Expenses
Interest	101,770	119,051
Depreciation and amortization	206,056	250,911
Operating expenses	680,663	813,932
Operating Partnerships Total Expenses	988,489	1,183,894
NET LOSS	(56,511)	(108,389)
Net loss allocation to Boston Capital Tax Credit Fund III L.P.	(55,946)	(107,305)
Net loss allocated to other Partners	(565)	(1,084)
Series 17
Revenues
Rental	421,068	579,160
Interest and other	7,653	11,751
Operating Partnerships Revenue	428,721	590,911
Expenses
Interest	63,503	53,055
Depreciation and amortization	119,488	171,868
Operating expenses	366,393	423,392
Operating Partnerships Total Expenses	549,384	648,315
NET LOSS	(120,663)	(57,404)
Net loss allocation to Boston Capital Tax Credit Fund III L.P.	(119,455)	(56,829)
Net loss allocated to other Partners	(1,208)	(575)
Series 18
Revenues
Rental	675,567	805,458
Interest and other	14,102	16,959
Operating Partnerships Revenue	689,669	822,417
Expenses
Interest	116,450	132,168
Depreciation and amortization	159,462	191,985
Operating expenses	587,644	715,697
Operating Partnerships Total Expenses	863,556	1,039,850
NET LOSS	(173,887)	(217,433)
Net loss allocation to Boston Capital Tax Credit Fund III L.P.	(172,148)	(215,259)
Net loss allocated to other Partners	(1,739)	(2,174)
Series 19
Revenues
Rental	0	89,827
Interest and other	0	7,751
Operating Partnerships Revenue	0	97,578
Expenses
Interest	0	6,613
Depreciation and amortization	0	4,898
Operating expenses	0	99,881
Operating Partnerships Total Expenses	0	111,392
NET LOSS	0	(13,814)
Net loss allocation to Boston Capital Tax Credit Fund III L.P.	0	(13,676)
Net loss allocated to other Partners	$ 0	$ (138)