Condensed Consolidated Statements of Partners' Capital (Unaudited) - USD ($)	Total	General Partner [Member]	Beneficial Unit Certificate Holders [Member]	Beneficial Unit Certificate Holders - Restricted and Unrestricted [Member]	Number of Units [Member]	Number of Units - Restricted and Unrestricted [Member]	Noncontrolling Interest [Member]	Accumulated Other Comprehensive Income (Loss) [Member]
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	(17,291,101)	(2,227,869)	(15,063,232)
Net income (loss) allocated to Partners and noncontrolling interests:
Net income (loss) allocable to Partners	13,410,851	2,189,068	11,221,896				(113)
Unrealized gain on securities	72,171,756	721,718	71,450,038					72,171,756
Unrealized gain on bond purchase commitments	11,584,459	115,845	11,468,614					11,584,459
Balance at Jun. 30, 2016	392,764,353	1,195,475	$ 391,563,505				5,373	144,483,463
Partners' Capital Account, Units at Jun. 30, 2016					60,252,928
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	(11,819,553)	(118,196)		(11,701,357)
Distribution of Tier 2 earnings (Note 3)	(4,482,500)	(1,120,625)		(3,361,875)
Net income (loss) allocated to Partners and noncontrolling interests:
Net income (loss) allocable to Partners	10,712,723	1,182,211		9,458,859			$ 71,653
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	609,733	6,097		603,636
Unrealized gain on securities	29,207,054	292,071		28,914,983				29,207,054
Unrealized gain on bond purchase commitments	765,723	7,657		758,066				765,723
Balance at Jun. 30, 2017	$ 303,584,510	$ 351,751		$ 303,232,759				$ 68,868,261
Partners' Capital Account, Units at Jun. 30, 2017						60,252,928