CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Statement of Cash Flows [Abstract]
Net income (loss)	$ (3,640,189)	$ (849,251)
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities
Amortization of premiums and discounts of investments, net	618,800	246,150
Amortization of securitized debt premiums and discounts and deferred financing costs	(2,881)	(3,627)
Depreciation, amortization and other noncash expenses	7,684	7,072
Net (gains) losses on disposals of investments and other	(206,583)	93,916
Net (gains) losses on investments and derivatives	3,749,018	458,086
Income from unconsolidated joint ventures	(370)	1,960
Loan loss provision	99,326	5,703
Payments on purchases of loans held for sale	(54,820)	(49,070)
Proceeds from sales and repayments of loans held for sale	61,664	44,817
Net receipts (payments) on derivatives	(2,680,933)	(633,221)
Net change in
Other assets	105,636	(107,040)
Interest receivable	115,341	(29,491)
Interest payable	(215,030)	(146,537)
Other liabilities	20,075	18,436
Net cash provided by (used in) operating activities	(2,023,262)	(942,097)
Cash flows from investing activities
Payments on purchases of securities	(11,526,904)	(18,472,733)
Proceeds from sales of securities	41,132,114	7,863,347
Principal payments on securities	4,900,580	2,386,243
Payments of purchases of loans	(1,148,574)	(664,002)
Proceeds from sales of loans	271,007	179,112
Principal payments on loans	471,384	676,499
Investments in real estate	(1,159)	(5,950)
Proceeds from sales of real estate	0	6,661
Proceeds from reverse repurchase agreements	27,150,000	28,107,306
Payments on reverse repurchase agreements	(27,150,000)	(27,980,715)
Distributions in excess of cumulative earnings from unconsolidated joint ventures	6,017	241
Net cash provided by (used in) investing activities	34,104,465	(7,903,991)
Cash flows from financing activities
Proceeds from repurchase agreements and other secured financing	1,126,771,986	1,411,469,975
Payments on repurchase agreements and other secured financing	(1,158,603,746)	(1,404,070,367)
Proceeds from issuances of securitized debt	1,394,065	905,265
Principal payments on securitized debt	(276,551)	(561,955)
Payment of deferred financing cost	0	(1,781)
Net proceeds from stock offerings, direct purchases and dividend reinvestments	0	1,319,709
Principal payments on mortgages payable	(811)	(722)
Net contributions (distributions) from (to) noncontrolling interests	(288)	(361)
Dividends paid	(393,066)	(426,819)
Net cash provided by (used in) financing activities	(31,108,411)	8,632,944
Net (decrease) increase in cash and cash equivalents	972,792	(213,144)
Cash and cash equivalents including cash pledged as collateral, beginning of period	1,850,729	1,539,746	$ 1,539,746
Cash and cash equivalents including cash pledged as collateral, end of period	2,823,521	1,326,602	1,850,729
Supplemental disclosure of cash flow information
Interest received	1,260,159	1,079,294
Dividends received	2,116	2,116
Interest paid (excluding interest paid on interest rate swaps)	575,973	633,805
Net interest paid on interest rate swaps	171,965	34,663
Taxes received (paid)	52	(30)
Noncash investing activities
Receivable for unsettled trades	1,006,853	1,574,251	4,792	[1]
Payable for unsettled trades	923,552	4,763,376	463,387	[1]
Net change in unrealized gains (losses) on available-for-sale securities, net of reclassification adjustment	983,180	1,660,489
Noncash financing activities
Dividends declared, not yet paid	$ 357,606	$ 434,431	$ 357,527	[1]

[1] Derived from the audited consolidated financial statements at December 31, 2019.