CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($)	3 Months Ended
	Mar. 31, 2019	Dec. 31, 2018		Mar. 31, 2018
Statement of Cash Flows [Abstract]
Net income (loss)	$ (849,251,000)			$ 1,327,704,000
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities
Amortization of premiums and discounts of investments, net	246,150,000			92,976,000
Amortization of securitized debt premiums and discounts and deferred financing costs	(3,627,000)			408,000
Depreciation, amortization and other noncash expenses	7,072,000			5,822,000
Net (gains) losses on disposals of investments	93,916,000			(13,468,000)
Net (gains) losses on investments and derivatives	458,086,000			(878,547,000)
Income from unconsolidated joint ventures	1,960,000			618,000
Loan loss provision	5,703,000	$ 3,500,000		0
Payments on purchases of loans held for sale	(49,070,000)			(37,190,000)
Proceeds from sales and repayments of loans held for sale	44,817,000			30,178,000
Net receipts (payments) on derivatives	(633,221,000)			951,021,000
Net change in
Other assets	(107,040,000)			(42,361,000)
Interest receivable	(29,491,000)			(2,963,000)
Interest payable	(146,537,000)			31,628,000
Other liabilities	18,436,000			(132,910,000)
Net cash provided by (used in) operating activities	(942,097,000)			1,332,916,000
Cash flows from investing activities
Payments on purchases of residential securities	(18,374,100,000)			(3,718,947,000)
Proceeds from sales of residential securities	7,822,334,000			463,214,000
Principal payments on residential securities	2,343,383,000			2,696,245,000
Payments on purchases of MSRs	0			(249,000)
Payments on purchases of corporate debt	(125,351,000)			(230,103,000)
Proceeds from sales of corporate debt	179,112,000			0
Principal payments on corporate debt	33,545,000			92,820,000
Originations and purchases of commercial real estate investments	(269,489,000)			(91,647,000)
Proceeds from sales of commercial real estate investments	41,013,000			9,556,000
Principal repayments on commercial real estate investments	578,031,000			130,555,000
Proceeds from sales of real estate	6,661,000			0
Proceeds from reverse repurchase agreements	28,107,306,000			20,050,112,000
Payments on reverse repurchase agreements	(27,980,715,000)			(20,250,571,000)
Distributions in excess of cumulative earnings from unconsolidated joint ventures	241,000			2,813,000
Payments on purchases of residential mortgage loans held for investment	(373,745,000)			(167,124,000)
Proceeds from repayments of residential mortgage loans held for investment	107,783,000			67,384,000
Net cash provided by (used in) investing activities	(7,903,991,000)			(945,942,000)
Cash flows from financing activities
Proceeds from repurchase agreements and other secured financing	1,411,469,975,000			1,299,589,620,000
Principal payments on repurchase agreements and other secured financing	(1,404,070,367,000)			(1,299,277,944,000)
Proceeds from issuances of securitized debt	905,265,000			279,203,000
Principal repayments on securitized debt	(561,955,000)			(317,773,000)
Payment of deferred financing cost	(1,781,000)			0
Net proceeds from stock offerings, direct purchases and dividend reinvestments	1,319,709,000			412,081,000
Redemptions of preferred stock	0			(412,500,000)
Principal payments on mortgages payable	(722,000)			0
Net contributions (distributions) from (to) noncontrolling interests	(361,000)			(333,000)
Dividends paid	(426,819,000)			(381,642,000)
Net cash provided by (used in) financing activities	8,632,944,000			(109,288,000)
Net (decrease) increase in cash and cash equivalents	(213,144,000)			277,686,000
Cash and cash equivalents including cash pledged as collateral, beginning of period	1,735,749,000			706,589,000
Cash and cash equivalents including cash pledged as collateral, end of period	1,522,605,000	1,735,749,000		984,275,000
Supplemental disclosure of cash flow information
Interest received	1,079,294,000			1,017,534,000
Dividends received	2,116,000			1,650,000
Interest paid (excluding interest paid on interest rate swaps)	633,805,000			320,988,000
Net interest paid on interest rate swaps	34,663,000			39,206,000
Taxes received (paid)	(30,000)			2,000
Noncash investing activities
Receivable for unsettled trades	1,574,251,000	68,779,000	[1]	45,126,000
Payable for unsettled trades	4,763,376,000	583,036,000	[1]	91,327,000
Net change in unrealized gains (losses) on available-for-sale securities, net of reclassification adjustment	1,660,489,000			(1,874,060,000)
Noncash financing activities
Dividends declared, not yet paid	$ 434,431,000	$ 394,129,000	[1]	$ 347,897,000

[1] (1) Derived from the audited consolidated financial statements at December 31, 2018.