Summary Quarterly Consolidated Financial Information - Unaudited (Details) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Summary Quarterly Consolidated Financial Information - Unaudited
Net interest income	$ 14,878,213	$ 14,140,346	$ 22,632,167	$ 13,282,028	$ 12,898,651	$ 17,323,926	$ 14,269,832	$ 14,320,477	$ 64,932,754	$ 58,812,886	$ 56,966,472
Total other revenue	4,917,135	7,254,484	7,278,650	8,486,343	6,056,465	8,962,195	9,151,570	10,116,484	27,936,612	34,286,714	32,417,974
Total other expenses	18,001,688	18,338,403	19,057,772	18,669,461	14,859,256	18,819,835	17,958,639	17,011,318	74,067,324	68,649,048	72,812,006
Income before gain on acceleration of deferred income, loss on termination of swaps, gain on sale of real estate and income from equity affiliates	1,793,660	3,056,427	10,853,045	3,098,910					18,802,042	24,450,552	16,572,440
Income before gain on sale of equity interests, incentive management fee, gain (loss) on sale of real estate and income (loss from equity affiliates					4,095,860	7,466,286	5,462,763	7,425,643
Gain on acceleration of deferred income		8,162,720		11,009,162					19,171,882
Loss on termination of swaps		(340,197)		(4,289,450)					(4,629,647)
Gain on sale of equity interests					819,067	77,123,133	7,851,266			85,793,466
Incentive management fee - equity interest - related party						(19,047,949)				(19,047,949)
Gain (loss) on sale of real estate	3,799,657			3,984,364	1,803,512	(199,749)			7,784,021	1,603,763
Income (loss) from equity affiliates	1,317,339	6,353,239	1,534,025	3,095,913	219,287	(51,170)	40,493	40,048	12,300,516	248,658	(204,475)
Net income	6,910,656	17,232,189	12,387,070	16,898,899	6,937,726	65,290,551	13,354,522	7,465,691	53,428,814	93,048,490	21,298,737
Preferred stock dividends	1,888,430	1,888,430	1,888,430	1,888,430	1,888,430	1,888,430	1,888,465	1,590,930	7,553,720	7,256,255	4,506,583
Net income attributable to common stockholders	$ 5,022,226	$ 15,343,759	$ 10,498,640	$ 15,010,469	$ 5,049,296	$ 63,402,121	$ 11,466,057	$ 5,874,761	$ 45,875,094	$ 85,792,235	$ 16,667,955
Basic earnings per common share (in dollars per share)	$ 0.10	$ 0.30	$ 0.21	$ 0.30	$ 0.10	$ 1.26	$ 0.23	$ 0.12	$ 0.90	$ 1.71	$ 0.39
Diluted earnings per common share (in dollars per share)	$ 0.10	$ 0.30	$ 0.21	$ 0.30	$ 0.10	$ 1.26	$ 0.23	$ 0.12	$ 0.90	$ 1.70	$ 0.39