EQUITY AND EARNINGS PER SHARE - Narrative (Details) $ / shares in Units, $ in Thousands							1 Months Ended				12 Months Ended
	Jan. 01, 2019 shares	Jul. 30, 2018 USD ($) $ / shares	Jan. 01, 2018 shares	Jan. 01, 2017 shares	Jan. 01, 2016 shares	Jan. 01, 2014 shares	Nov. 30, 2018 USD ($) $ / shares shares	Jan. 31, 2018 USD ($) $ / shares shares	Feb. 28, 2017 USD ($) employee $ / shares shares	Aug. 31, 2016 USD ($) $ / shares shares	Dec. 31, 2018 USD ($) $ / shares shares	Dec. 31, 2017 USD ($) $ / shares shares	Dec. 31, 2016 USD ($) shares
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Common stock, shares authorized (in shares)											2,000,000,000	2,000,000,000
Common stock, par value (in dollars per share) | $ / shares											$ 0.01	$ 0.01
Preferred stock, shares authorized (in shares)											100,000,000.0
Preferred stock, par value (in dollars per share) | $ / shares											$ 0.01
Issuance of common stock (in shares)							28,800,000	28,800,000
Share price (in dollars per share) | $ / shares							$ 17.32	$ 17.10
Proceeds from issuance of common stock | $							$ 489,200	$ 482,300	$ 834,500	$ 278,800	$ 983,149	$ 835,465	$ 279,600
Options granted to Manager (in shares)							2,900,000	2,900,000
Fair value of options granted to Manager | $							$ 3,800	$ 3,800
Risk-free interest rate							3.25%	2.58%	2.38%	1.45%
Dividend yield							8.61%	9.86%	10.82%	11.80%
Volatility							17.50%	23.16%	28.64%	27.57%
Term (in years)							10 years	10 years	10 years	10 years
Options granted (in shares)											5,799,166	5,654,578
Common stock, shares outstanding (in shares)											369,104,429	307,361,309
Reserved shares of common stock for issuance (in shares)											15,000,000
Stock option plan term (in years)											10 years
Yearly increase in number of shares available for options											10.00%
Number of additional shares authorized (in shares)			5,654,578	2,000,000	8,543,539	0
Threshold percentage for options that may be issued to the Manager											10.00%
Stock options outstanding (in shares)											8,498,138
Share price (in dollars per share) | $ / shares											$ 14.21
Shares of dilutive common stock equivalents (in shares)											1,868,438	364,107	2,167,796
Subsequent Event
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Number of additional shares authorized (in shares)	5,799,166
Executive Officer
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Number of employees | employee									1
Fortress-managed funds
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Common stock, shares outstanding (in shares)											2,400,000
Director
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Stock options outstanding (in shares)											6,000	6,000
Director | Equity Option
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Stock options outstanding (in shares)											6,000
Common Stock
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Issuance of common stock (in shares)									56,500,000.0	20,000,000.0
Share price (in dollars per share) | $ / shares									$ 15.00	$ 14.20
Options granted to Manager (in shares)									5,700,000.0	2,000,000.0
Fair value of options granted to Manager | $									$ 8,100	$ 2,300
Common Stock | Executive Officer
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Issuance of common stock (in shares)									18,600
Common Stock
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Issuance of common stock (in shares)											57,991,659	56,545,787	20,000,000
Distribution Agreement
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Common stock, par value (in dollars per share) | $ / shares		$ 0.01
Distribution Agreement | Common Stock
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Aggregate offering price | $		$ 500,000									$ 9,100
Shares sold (in shares)											500,000
Options granted (in shares)											50,000
Fair value of grants | $											$ 100