SUMMARIZED QUARTERLY RESULTS (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Quarterly Financial Information Disclosure [Abstract]
Interest income	$ 745,423	$ 622,550	$ 537,426	$ 587,727	$ 807,022	$ 558,668	$ 457,118	$ 388,143	$ 2,493,126	$ 2,210,951	$ 2,170,697
Interest expense	318,711	268,937	222,281	198,425	183,396	174,154	152,755	147,447	1,008,354	657,752	471,596
Net interest income	426,712	353,613	315,145	389,302	623,626	384,514	304,363	240,696	1,484,772	1,553,199	1,699,101
Total realized and unrealized gains (losses)	359,215	43,807	(277,794)	74,265	1,250,636	412,906	(523,785)	(1,055,553)	199,493	84,204	(1,021,351)
Total other income (loss)	25,064	28,282	30,865	31,646	30,918	29,271	(9,930)	(6,115)
Less: Total general and administrative expenses	59,257	57,016	54,023	53,828	55,453	97,737	49,221	47,945
Income (loss) before income taxes	751,734	368,686	14,193	441,385	1,849,727	728,954	(278,573)	(868,917)	1,575,998	1,431,191	463,793
Less: Income taxes	4,963	1,371	(329)	977	1,244	(1,926)	(76)	(837)	6,982	(1,595)	(1,954)
Net income (loss)	746,771	367,315	14,522	440,408	1,848,483	730,880	(278,497)	(868,080)	1,569,016	1,432,786	465,747
Less: Net income attributable to noncontrolling interest	(151)	(232)	(102)	(103)	(87)	(336)	(385)	(162)	(588)	(970)	(809)
Less: Dividends on preferred stock	32,334	30,355	23,473	23,473	23,473	22,803	17,992	17,992	109,635	82,260	71,968
Net income (loss) available (related) to common stockholders	$ 714,588	$ 337,192	$ (8,849)	$ 417,038	$ 1,825,097	$ 708,413	$ (296,104)	$ (885,910)	$ 1,459,969	$ 1,351,496	$ 394,588
Net income (loss) available (related) per share to common stockholders:
Basic (in dollars per share)	$ 0.62	$ 0.31	$ (0.01)	$ 0.41	$ 1.79	$ 0.70	$ (0.32)	$ (0.96)	$ 1.37	$ 1.39	$ 0.42
Diluted (in dollars per share)	$ 0.62	$ 0.31	$ (0.01)	$ 0.41	$ 1.79	$ 0.70	$ (0.32)	$ (0.96)	$ 1.37	$ 1.39	$ 0.42
6.95% Series F Fixed-to-Floating Rate Cumulative Redeemable Preferred Stock
Class of Stock [Line Items]
Cumulative and undeclared dividends		$ 8,300