Condensed Consolidated Statements of Partners' Capital (Unaudited) - USD ($)	Total	Tier 2 [Member]	Tier 3 [Member]	General Partner [Member]	General Partner [Member] Tier 2 [Member]	BUCs - Restricted and Unrestricted [Member]	BUCs - Restricted and Unrestricted [Member] Tier 2 [Member]	BUCs - Restricted and Unrestricted [Member] Tier 3 [Member]	Number of BUCs - Restricted and Unrestricted [Member]	Accumulated Other Comprehensive Income (Loss) [Member]
Balance at Dec. 31, 2019	$ 341,938,263			$ 735,128		$ 341,203,135				$ 99,308,677
Partners' Capital Account, Units at Dec. 31, 2019									60,835,204
Distributions paid or accrued:
Regular distribution	(8,050,119)			(80,501)		(7,969,618)
Distribution of (income) loss (Note 3)		$ 445,719			$ 80,501		$ 365,218
Net income (loss) allocable to Partners	2,263,994			(53,404)		2,317,398
Repurchase of BUCs, Value	(2,106,673)					(2,106,673)
Repurchase of BUCs, Units									(290,000)
Restricted units awarded									290,000
Restricted unit compensation expense	39,068			391		38,677
Unrealized gain (loss) on securities	(7,057,736)			(70,577)		(6,987,159)				(7,057,736)
Reversal of net unrealized gains on sale of securities	(1,408,804)			(14,088)		(1,394,716)				(1,408,804)
Reversal of net unrealized loss on securities to provision for credit loss	372,169			3,722		368,447				372,169
Balance at Mar. 31, 2020	326,435,881			601,172		325,834,709				91,214,306
Partners' Capital Account, Units at Mar. 31, 2020									60,835,204
Balance at Dec. 31, 2019	341,938,263			735,128		341,203,135				99,308,677
Partners' Capital Account, Units at Dec. 31, 2019									60,835,204
Distributions paid or accrued:
Net income (loss) allocable to Partners	4,256,800
Reversal of net unrealized loss on securities to provision for credit loss										652,880
Balance at Sep. 30, 2020	361,159,616			948,408		360,211,208				130,723,408
Partners' Capital Account, Units at Sep. 30, 2020									60,835,204
Balance at Mar. 31, 2020	326,435,881			601,172		325,834,709				91,214,306
Partners' Capital Account, Units at Mar. 31, 2020									60,835,204
Distributions paid or accrued:
Regular distribution	(3,686,982)			(36,870)		(3,650,112)
Net income (loss) allocable to Partners	3,870,586			38,706		3,831,880
Restricted unit compensation expense	296,268			2,962		293,306
Unrealized gain (loss) on securities	20,971,649			209,716		20,761,933				20,971,649
Balance at Jun. 30, 2020	347,887,402			815,686		347,071,716				112,185,955
Partners' Capital Account, Units at Jun. 30, 2020									60,835,204
Distributions paid or accrued:
Regular distribution	(3,686,983)			(36,870)		(3,650,113)
Net income (loss) allocable to Partners	(1,877,780)			(18,778)		(1,859,002)
Restricted unit compensation expense	299,524			2,996		296,528
Unrealized gain (loss) on securities	18,000,520			180,005		17,820,515				18,000,520
Unrealized gain (loss) on bond purchase commitments	256,222			2,562		253,660				256,222
Reversal of net unrealized loss on securities to provision for credit loss	280,711			2,807		277,904				280,711
Balance at Sep. 30, 2020	361,159,616			948,408		360,211,208				130,723,408
Partners' Capital Account, Units at Sep. 30, 2020									60,835,204
Balance at Dec. 31, 2020	359,772,042			934,892		358,837,150				132,594,007
Partners' Capital Account, Units at Dec. 31, 2020									60,823,674
Distributions paid or accrued:
Regular distribution	(3,401,314)			(34,013)		(3,367,301)
Distribution of (income) loss (Note 3)		(2,809,106)			(702,277)		(2,106,829)
Net income (loss) allocable to Partners	6,275,091			736,936		5,538,155
Restricted unit compensation expense	78,114			781		77,333
Unrealized gain (loss) on securities	(16,298,797)			(162,988)		(16,135,809)				(16,298,797)
Unrealized gain (loss) on bond purchase commitments	(120,970)			(1,210)		(119,760)				(120,970)
Balance at Mar. 31, 2021	343,495,060			772,121		342,722,939				116,174,240
Partners' Capital Account, Units at Mar. 31, 2021									60,823,674
Balance at Dec. 31, 2020	359,772,042			934,892		358,837,150				132,594,007
Partners' Capital Account, Units at Dec. 31, 2020									60,823,674
Distributions paid or accrued:
Net income (loss) allocable to Partners	28,092,630
Balance at Sep. 30, 2021	377,472,418			813,097		376,659,321				113,611,581
Partners' Capital Account, Units at Sep. 30, 2021									66,330,039
Balance at Mar. 31, 2021	343,495,060			772,121		342,722,939				116,174,240
Partners' Capital Account, Units at Mar. 31, 2021									60,823,674
Distributions paid or accrued:
Regular distribution	(2,624,057)			(26,241)		(2,597,816)
Distribution of (income) loss (Note 3)		(5,463,484)			(1,365,870)		(4,097,614)
Net income (loss) allocable to Partners	9,546,917			1,406,706		8,140,211
Repurchase of BUCs, Value	(1,363,736)					(1,363,736)
Repurchase of BUCs, Units									(222,459)
Restricted units awarded									266,324
Restricted unit compensation expense	190,970			1,910		189,060
Unrealized gain (loss) on securities	1,933,172			19,332		1,913,840				1,933,172
Unrealized gain (loss) on bond purchase commitments	81,606			816		80,790				81,606
Balance at Jun. 30, 2021	345,796,448			808,774		344,987,674				118,189,018
Partners' Capital Account, Units at Jun. 30, 2021									60,867,539
Distributions paid or accrued:
Distribution of (income) loss (Note 3)		$ (2,139,488)	$ (5,691,689)		$ (534,873)		$ (1,604,615)	$ (5,691,689)
Net income (loss) allocable to Partners	12,270,622			579,266		11,691,356
Sale of BUCs, net of issuance costs, Value	31,243,495					31,243,495
Sale of BUCs, net of issuance costs, Units									5,462,500
Restricted unit compensation expense	570,467			5,705		564,762
Unrealized gain (loss) on securities	(4,586,145)			(45,862)		(4,540,283)				(4,586,145)
Unrealized gain (loss) on bond purchase commitments	8,708			87		8,621				8,708
Balance at Sep. 30, 2021	$ 377,472,418			$ 813,097		$ 376,659,321				$ 113,611,581
Partners' Capital Account, Units at Sep. 30, 2021									66,330,039