Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Assets:
Pledged MBS	$ 2,730,427	$ 2,640,884
Pledged U.S. Treasuries	$ 73,343	$ 124,215
Shareholders’ Equity:
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	50,000,000	50,000,000
Preferred stock, shares issued	5,908,999	5,888,680
Preferred stock, shares outstanding	5,908,999	5,888,680
Preferred stock, aggregate liquidation preference	$ 147,725	$ 147,217
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	200,000,000	200,000,000
Common stock, shares issued	55,996,048	55,831,549
Common stock, shares outstanding	55,996,048	55,831,549