Consolidated Statements of Comprehensive Income (Loss) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Comprehensive Income [Abstract]
Net income (loss)	$ 4,706,961	$ (7,989,955)	$ 450,479
Other comprehensive income (loss):
Increase (decrease) in net unrealized gain (loss) on available-for-sale securities, net	(13,268,331)	(3,824,461)	(14,776,266)
Reclassification adjustment for net gain (loss) included in net income (loss)	7,482,477	(5,589,740)	1,969,108
Reclassification adjustment for other-than-temporary impairments included in net income (loss)	0	541,342	745,492
Reclassification cumulative adjustment for Linked Transactions	0	0	4,457,544
Total other comprehensive income (loss)	(5,785,854)	(8,872,859)	(7,604,122)
Less: Dividends to preferred stockholders	(3,522,036)	(3,522,036)	(3,522,036)
Comprehensive income (loss) attributable to common stockholders	$ (4,600,929)	$ (20,384,850)	$ (10,675,679)