ACQUISITION OF MTGE INVESTMENT CORP - Summary of Acquired Assets (Details) - USD ($) $ in Thousands		Sep. 07, 2018	Jun. 30, 2019	Dec. 31, 2018		Jun. 30, 2018
Net Assets:
Cash and cash equivalents	[1]		$ 1,982,311	$ 1,735,749	[2]
Securities			119,926,869	92,623,788
Real estate, net			733,196	739,473	[2]
Derivative assets			75,142	200,503	[2]
Reverse repurchase agreements			0	650,040	[2]
Receivable for unsettled trades			5,322	68,779	[2]	$ 21,728
Interest receivable			440,940	357,365	[2]
Intangible assets, net			96,591	100,854	[2]
Other assets			357,027	333,988	[2]
Total assets			131,800,776	105,787,527	[2]
Repurchase agreements			105,181,241	81,115,874	[2]
Mortgages payable			498,772	511,056	[2]
Derivative liabilities			1,043,197	889,750	[2]
Interest payable			691,327	570,928	[2]
Dividends payable			364,066	394,129	[2]	$ 349,300
Other liabilities			95,825	74,580	[2]
Total liabilities			$ 116,093,369	$ 91,669,726	[2]
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] ⁽²⁾  Includes cash of consolidated Variable Interest Entities (“VIEs”) of $48.3 million and $30.4 million at June 30, 2019 and December 31, 2018, respectively.

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