SUMMARIZED QUARTERLY RESULTS (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Interest income	$ 859,674	$ 816,596	$ 776,806	$ 879,487	$ 745,423	$ 622,550	$ 537,426	$ 587,727	$ 3,332,563	$ 2,493,126	$ 2,210,951
Interest expense	586,774	500,973	442,692	367,421	318,711	268,937	222,281	198,425	1,897,860	1,008,354	657,752
Net interest income	272,900	315,623	334,114	512,066	426,712	353,613	315,145	389,302	1,434,703	1,484,772	1,553,199
Total realized and unrealized gains (losses)	(2,502,035)	199,716	294,646	844,689	359,215	43,807	(277,794)	74,265	(1,162,984)	199,493	84,204
Total other income (loss)	52,377	(10,643)	34,170	34,023	25,064	28,282	30,865	31,646
Less: Total general and administrative expenses	77,073	126,509	63,781	62,510	59,257	57,016	54,023	53,828
Income (loss) before income taxes	(2,253,831)	378,187	599,149	1,328,268	751,734	368,686	14,193	441,385	51,773	1,575,998	1,431,191
Less: Income taxes	1,041	(7,242)	3,262	564	4,963	1,371	(329)	977	(2,375)	6,982	(1,595)
Net income (loss)	(2,254,872)	385,429	595,887	1,327,704	746,771	367,315	14,522	440,408	54,148	1,569,016	1,432,786
Less: Net income attributable to noncontrolling interests	17	(149)	(32)	(96)	(151)	(232)	(102)	(103)	(260)	(588)	(970)
Dividends on preferred stock	32,494	31,675	31,377	33,766	32,334	30,355	23,473	23,473	129,312	109,635	82,260
Net income (loss) available (related) to common stockholders	$ (2,287,383)	$ 353,903	$ 564,542	$ 1,294,034	$ 714,588	$ 337,192	$ (8,849)	$ 417,038	$ (74,904)	$ 1,459,969	$ 1,351,496
Net income (loss) available (related) per share to common stockholders:
Basic (in dollars per share)	$ (1.74)	$ 0.29	$ 0.49	$ 1.12	$ 0.62	$ 0.31	$ (0.01)	$ 0.41	$ (0.06)	$ 1.37	$ 1.39
Diluted (in dollars per share)	$ (1.74)	$ 0.29	$ 0.49	$ 1.12	$ 0.62	$ 0.31	$ (0.01)	$ 0.41	$ (0.06)	$ 1.37	$ 1.39
6.95% Series F Fixed-to-Floating Rate Cumulative Redeemable Preferred Stock
Class of Stock [Line Items]
Cumulative and undeclared dividends		$ 8,300