Condensed Consolidated Statements of Comprehensive Income (Loss) (Unaudited) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Net income	$ 3,338,121	$ 4,109,400	$ 9,342,425	$ 11,469,915
Reversal of net unrealized losses on securities with other-than-temporary impairment			525,446
Unrealized gain (loss) on bond purchase commitments			(2,007,855)	765,723
Comprehensive income (loss)	7,352,346	14,880,867	(9,493,293)	41,442,692
Comprehensive income allocated to noncontrolling interest				71,653
Partnership comprehensive income (loss)	7,352,346	14,880,867	(9,493,293)	41,371,039
Accumulated Other Comprehensive Income (Loss) [Member]
Net income	3,338,121	4,109,400	9,342,425	11,469,915
Reversal of net unrealized losses on securities with other-than-temporary impairment	981,792		525,446
Unrealized gain (loss) on securities	4,065,221	10,226,688	(17,353,309)	29,207,054
Unrealized gain (loss) on bond purchase commitments			(2,007,855)	765,723
Commitments [Member] | Accumulated Other Comprehensive Income (Loss) [Member]
Unrealized gain (loss) on bond purchase commitments	$ (1,032,788)	$ 544,779	$ (2,007,855)	$ 765,723