Consolidated Statements of Comprehensive Income - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Interest income	$ 94,502	$ 91,898	$ 100,244
Interest expense	36,178	25,231	22,605
Net interest income	58,324	66,667	77,639
Gain (loss) on derivative instruments, net	3,044	(5,606)	(43,128)
Loss on sale of investments, net	(11,530)	(4,238)	(978)
Fair value adjustments, net	75	103	69
Other (loss) income, net	(201)	880	610
General and administrative expenses:
Compensation and benefits	(8,509)	(7,550)	(9,103)
Other general and administrative	(7,310)	(7,157)	(8,565)
Net income	33,893	43,099	16,544
Preferred stock dividends	10,794	9,185	9,176
Net income to common shareholders	23,099	33,914	7,368
Other comprehensive income:
Unrealized gain (loss) on available-for-sale investments, net	12,650	(23,828)	(38,561)
Reclassification adjustment for loss on sale of investments, net	11,530	4,238	978
Reclassification adjustment for de-designated cash flow hedges	(268)	(251)	3,499
Total other comprehensive income (loss)	23,912	(19,841)	(34,084)
Comprehensive income (loss) to common shareholders	$ 47,011	$ 14,073	$ (26,716)
Net income per common share-basic and diluted	$ 0.46	$ 0.69	$ 0.14
Weighted average common shares-basic and diluted	50,417	49,114	52,847