ACQUISITION OF MTGE INVESTMENT CORP. - Summary of Acquired Assets (Details) - USD ($) $ in Thousands		Sep. 07, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Net Assets:
Cash and cash equivalents	[1]		$ 1,850,729	$ 1,735,749
Securities			114,833,580	92,623,788
Real estate, net			725,638	739,473
Derivative assets			113,556	200,503
Reverse repurchase agreements			0	650,040
Receivable for unsettled trades			4,792	68,779	$ 1,232
Principal receivable	[2]		4,462,350	4,585,975
Intangible assets, net			92,772	100,854
Other assets			381,220	333,988
Total assets			130,295,081	105,787,527
Repurchase agreements			101,740,728	81,115,874
Mortgages payable			485,005	511,056
Derivative liabilities			803,866	889,750
Interest payable			476,335	570,928
Dividends payable			357,527	394,129	$ 347,876
Other liabilities			93,388	74,580
Total liabilities			$ 114,498,737	$ 91,669,726
Mountain Merger Sub Corporation
Consideration Transferred:
Cash		$ 450,287
Equity issued		455,900
Total consideration		961,230
Net Assets:
Cash and cash equivalents		191,953
Securities		4,111,930
Real estate, net		277,648
Derivative assets		18,629
Reverse repurchase agreements		938,251
Receivable for unsettled trades		6,809
Principal receivable		44,462
Interest receivable		14,282
Intangible assets, net		14,483
Other assets		50,105
Total assets		5,668,552
Repurchase agreements		3,561,816
Mortgages payable		201,629
U.S. Treasury securities sold, not yet purchased		934,149
Derivative liabilities		2,498
Interest payable		22,220
Dividends payable		819
Other liabilities		28,715
Total liabilities		4,751,846
Net assets acquired		916,706
Common Stock | Mountain Merger Sub Corporation
Consideration Transferred:
Equity issued		455,943
Preferred Stock | Mountain Merger Sub Corporation
Consideration Transferred:
Equity issued		$ 55,000

[1] Includes cash of consolidated Variable Interest Entities (“VIEs”) of $67.5 million and $30.4 million at December 31, 2019 and 2018, respectively.

[2] Includes $66.7 million and $97.5 million of residential mortgage loans held for sale and $0 and $42.2 million of commercial mortgage loans held for sale at December 31, 2019 and 2018, respectively.