Quarterly Results of Operations – Unaudited (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Total revenues	$ 45,015	$ 43,397	$ 41,730	$ 40,880	$ 39,413	$ 37,899	$ 37,238	$ 37,107	$ 171,022	$ 151,657	$ 132,484
Total costs and expenses	(29,724)	(27,275)	(28,115)	(27,071)	(26,912)	(24,712)	(25,099)	(25,708)	(112,185)	(102,431)	(93,435)
Total other income and (expenses)	(470)	(1,338)	(3,236)	1,723	10,471	(3,065)	7,998	(1,342)	(3,321)	14,063	14,046
Net income	14,821	14,784	10,379	15,532	22,972	10,122	20,137	10,057	55,516	63,289	53,095
Net income, net of redemption of preferred stock and preferred stock dividends	$ 14,727	$ 14,689	$ 10,315	$ 15,434	$ 22,827	$ 10,056	$ 20,012	$ 9,992	$ 55,516	$ 63,289	$ 49,367
Earnings per Common Share – Basic and Diluted:
Net income available to common stockholders, basic (in dollars per share)	$ 0.22	$ 0.22	$ 0.16	$ 0.25	$ 0.38	$ 0.17	$ 0.35	$ 0.18	$ 0.86	$ 1.09	$ 0.95
Net income available to common stockholders, diluted (in dollars per share)	$ 0.22	$ 0.22	$ 0.16	$ 0.25	$ 0.38	$ 0.17	$ 0.35	$ 0.18	$ 0.85	$ 1.09	$ 0.95
Basic Weighted Average Common Shares Outstanding (in shares)	66,706,245	65,724,426	63,780,645	61,456,965	59,689,965	58,369,252	56,698,959	55,127,580	64,428,406	57,486,399	51,357,719
Diluted Weighted Average Common Shares Outstanding (in shares)	67,000,815	66,018,996	64,075,215	61,604,250	59,689,965	58,369,252	56,698,959	55,127,580	64,722,976	57,486,399	51,357,719