Income Taxes - Reconciliation of GAAP Net Income to Estimated REIT Taxable Income (Details) - USD ($)
$ in Thousands
3 Months Ended 9 Months Ended
Feb. 27, 2020
Sep. 30, 2020
Jun. 30, 2020
Mar. 31, 2020
Sep. 30, 2019
Jun. 30, 2019
Mar. 31, 2019
Sep. 30, 2020
Sep. 30, 2019
Income Tax Disclosure [Abstract]                  
GAAP net income (loss)   $ 58,386 $ 51,748 $ (406,659) $ (60,955) $ (183,250) $ (114,381) $ (296,525) $ (358,586)
Book to tax differences:                  
TRS (income) loss   145     (27)     76 (180)
Premium amortization expense   (103)     0     (183) 0
Agency Securities, trading   (12,149)     0     (20,060) 0
Credit Risk and Non-Agency Securities   6,510     10,051     188,075 25,973
Interest-Only Securities   0     0     0 85
U.S. Treasury Securities   0     736     (21,357) (2,024)
Changes in interest rate contracts   (29,199)     88,733     334,312 442,554
Credit loss expense   0     0     1,012 0
Gain on Security Sales   (9,468)     (4,569)     (138,802) (1,615)
Amortization of deferred hedging costs   (45,458)     (20,817)     (106,618) (49,868)
Series B Cumulative Preferred Stock dividend - Called for redemption $ (1,375) 0     0     1,375 0
Other   561     2     1,032 11
Estimated REIT taxable income (loss)   $ (30,775)     $ 13,154     $ (57,663) $ 56,350