Consolidated Statements of Partners' Capital - USD ($)	Total	Tier 2 [Member]	Tier 3 [Member]	General Partner [Member]	General Partner [Member] Tier 2 [Member]	Beneficial Unit Certificate Holders - Restricted and Unrestricted [Member]	Beneficial Unit Certificate Holders - Restricted and Unrestricted [Member] Tier 2 [Member]	Beneficial Unit Certificate Holders - Restricted and Unrestricted [Member] Tier 3 [Member]	Unallocated Deficit of Consolidated VIEs [Member]	Number of Units - Restricted and Unrestricted [Member]	Noncontrolling Interest [Member]	Accumulated Other Comprehensive Income (Loss) [Member]
Balance at Dec. 31, 2014	$ 309,927,904			$ 578,238		$ 330,457,117			$ (21,091,456)		$ (15,995)	$ 51,698,418
Partners' Capital Account, Units at Dec. 31, 2014										60,252,928
Bond redemption related to MF Property acquisition	(630,919)			(6,309)		(624,610)						(630,919)
Sale of MF Property	24,282										24,282
Deconsolidation of VIEs				(173,701)		(17,196,359)			17,370,059
Distributions paid or accrued:
Regular distribution	(23,343,025)			(233,430)		(23,109,595)
Distribution earnings		$ (9,355,825)			$ (2,338,956)		$ (7,016,869)
Net income (loss) allocable to Partners	26,606,222			2,474,274		20,413,352			$ 3,721,397		(2,801)
Unrealized Gain (Loss) on Securities	10,042,241			100,422		9,941,819						10,042,241
Unrealized gain (loss) on bond purchase commitment	(146,053)			(1,461)		(144,592)						(146,053)
Balance at Dec. 31, 2015	313,124,827			399,077		312,720,264					5,486	60,963,687
Partners' Capital Account, Units at Dec. 31, 2015										60,252,928
Reversal of net unrealized gain on sale of securities	(236,439)			(2,364)		(234,075)						(236,439)
Distributions paid or accrued:
Regular distribution	(21,764,612)			(217,646)		(21,546,966)
Distribution earnings		(11,434,599)			(2,858,650)		(8,575,949)
Net income (loss) allocable to Partners	23,200,277			2,992,106		20,208,994					(823)
Repurchase of Beneficial Unit Certificates	(1,603,658)					(1,603,658)
Repurchase of Beneficial Unit Certificates, Units										(272,307)
Restricted units awarded										272,307
Restricted units compensation expense	833,142			8,331		824,811
Beneficial unit certificates surrendered to pay tax withholding on vested restricted units, values	(153,306)					(153,306)
Beneficial Unit Certificates surrendered to pay tax withholding on vested restricted units										(28,390)
Unrealized Gain (Loss) on Securities	(18,596,853)			(185,969)		(18,410,884)						(18,596,853)
Unrealized gain (loss) on bond purchase commitment	(3,234,911)			(32,349)		(3,202,562)						(3,234,911)
Balance at Dec. 31, 2016	280,133,868			102,536		280,026,669					4,663	38,895,484
Partners' Capital Account, Units at Dec. 31, 2016										60,224,538
Distribution to noncontrolling interest	(76,316)										(76,316)
Distributions paid or accrued:
Regular distribution	(19,427,246)			(194,272)		(19,232,974)
Distribution earnings		$ (7,978,073)	$ (4,928,231)		$ (1,994,518)		$ (5,983,555)	$ (4,928,231)
Net income (loss) allocable to Partners	28,680,313			2,140,074		26,468,586					$ 71,653
Sale of Beneficial Unit Certificates, net of issuance costs, value	805,890					805,890
Sale of Beneficial Unit Certificates, net of issuance costs, unit										161,383
Repurchase of Beneficial Unit Certificates	(1,466,222)					(1,466,222)
Repurchase of Beneficial Unit Certificates, Units										(254,656)
Restricted units awarded										283,046
Restricted units compensation expense	1,615,242			16,152		1,599,090
Beneficial unit certificates surrendered to pay tax withholding on vested restricted units, values	(247,301)					(247,301)
Beneficial Unit Certificates surrendered to pay tax withholding on vested restricted units										(40,637)
Unrealized Gain (Loss) on Securities	36,797,352			367,974		36,429,378						36,797,352
Unrealized gain (loss) on bond purchase commitment	603,091			6,031		597,060						603,091
Reversal of net unrealized gain on securities with other-than-temporary impairment	(672,097)			(6,721)		(665,376)						(672,097)
Balance at Dec. 31, 2017	$ 313,840,270			$ 437,256		$ 313,403,014						$ 75,623,830
Partners' Capital Account, Units at Dec. 31, 2017										60,373,674