Consolidated Statements of Cash Flows - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Net Income (Loss)	$ (249,905,000)	$ (105,966,000)	$ 181,154,000
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:
Net amortization of premium on Agency Securities	53,909,000	32,989,000	44,838,000
Realized (gain) loss on sale of Agency Securities	(9,611,000)	152,950,000	8,486,000
Other than temporary impairment of Agency Securities	0	12,090,000	13,707,000
Stock based compensation	2,694,000	2,397,000	937,000
Changes in operating assets and liabilities:
Increase in accrued interest receivable	(12,443,000)	(53,000)	(3,713,000)
Increase in prepaid and other assets	(1,690,000)	(255,000)	(100,000)
Change in derivatives, at fair value	134,631,000	(58,145,000)	(69,081,000)
Increase (decrease) in accrued interest payable- repurchase agreements	21,664,000	3,816,000	(482,000)
Increase (decrease) in accounts payable and other accrued expenses	(821,000)	652,000	(4,003,000)
Net cash and cash collateral posted to counterparties provided by (used in) operating activities	(40,717,000)	75,223,000	110,079,000
Cash Flows From Investing Activities:
Purchases of Agency Securities	(8,937,989,000)	(4,816,961,000)	(5,813,389,000)
Principal repayments of Agency Securities	1,701,406,000	691,934,000	775,181,000
Principal repayments of Credit Risk and Non-Agency Securities	53,641,000	33,837,000	145,731,000
Proceeds from sales of Agency Securities	2,894,339,000	4,496,015,000	4,012,398,000
Increase (decrease) in cash collateral posted by counterparties	(82,255,000)	67,620,000	25,819,000
Subordinated loan to BUCKLER	0	0	(105,000,000)
Net cash and cash collateral posted to counterparties provided by (used in) investing activities	(4,389,771,000)	466,258,000	(959,112,000)
Cash Flows From Financing Activities:
Issuance of common stock, net of expenses	321,860,000	38,014,000	133,193,000
Proceeds from repurchase agreements	173,216,266,000	185,437,769,000	141,685,213,000
Principal repayments on repurchase agreements	(168,899,370,000)	(185,956,035,000)	(140,947,749,000)
Common stock dividends paid	(124,477,000)	(97,024,000)	(89,409,000)
Common stock repurchased	(16,965,000)	0	0
Net cash and cash collateral posted to counterparties provided by (used in) financing activities	4,471,455,000	(591,676,000)	780,183,000
Net increase (decrease) in cash and cash collateral posted to counterparties	40,967,000	(50,195,000)	(68,850,000)
Cash and cash collateral posted to counterparties - beginning of year	232,199,000	282,394,000	351,244,000
Cash and cash collateral posted to counterparties - end of year	273,166,000	232,199,000	282,394,000
Supplemental Disclosure:
Cash paid during the year for interest	425,746,000	252,393,000	164,913,000
Non-Cash Investing Activities:
Payable for unsettled purchases	358,712,000	166,052,000	0
Net unrealized gain (loss) on available for sale Agency Securities	408,954,000	(188,799,000)	(13,170,000)
Amounts receivable for issuance of preferred stock	5,506,000	0	153,000
Amounts payable for common stock repurchased	(803,000)	0	0
Series A Preferred Stock
Cash Flows From Financing Activities:
Redemption of Series A Preferred stock, net of expenses	(54,514,000)	0	0
Preferred dividends paid	(2,249,000)	(4,498,000)	(4,498,000)
Series B Preferred Stock
Cash Flows From Financing Activities:
Issuance of Series B Preferred stock, net of expenses	44,289,000	2,632,000	14,815,000
Preferred dividends paid	(13,385,000)	(12,534,000)	(11,382,000)
Credit Risk and Non-Agency Securities
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:
Accretion of net discount on Credit Risk and Non-Agency Securities	(2,956,000)	(2,946,000)	(3,866,000)
(Gain) loss on trading securities	24,396,000	27,266,000	(65,672,000)
Cash Flows From Investing Activities:
Purchases of trading securities	(138,767,000)	0	(8,224,000)
Principal repayments of Credit Risk and Non-Agency Securities	53,641,000	33,837,000
Proceeds from sale of trading securities	0	97,758,000	8,372,000
Interest-Only Securities
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:
Accretion of net discount on Credit Risk and Non-Agency Securities	1,924,000	4,122,000	4,908,000
(Gain) loss on trading securities	(123,000)	1,007,000	2,966,000
Cash Flows From Investing Activities:
Purchases of trading securities	0	0
Principal repayments of Credit Risk and Non-Agency Securities	0	0
Proceeds from sale of trading securities	18,822,000	0	0
U.S. Treasury Securities
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:
Accretion of net discount on Credit Risk and Non-Agency Securities	(362,000)	(1,066,000)	0
(Gain) loss on trading securities	(2,024,000)	6,365,000	0
Cash Flows From Investing Activities:
Purchases of trading securities	(1,685,058,000)	(765,828,000)	0
Principal repayments of Credit Risk and Non-Agency Securities	0	0
Proceeds from sale of trading securities	$ 1,786,090,000	$ 661,883,000	$ 0