Annual report pursuant to Section 13 and 15(d)

EQUITY AND EARNINGS PER SHARE EQUITY AND EARNINGS PER SHARE - Outstanding Options Narrative (Details)

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EQUITY AND EARNINGS PER SHARE EQUITY AND EARNINGS PER SHARE - Outstanding Options Narrative (Details) - USD ($)
$ / shares in Units, $ in Millions
 3 Months Ended 12 Months Ended
May 07, 2015
Mar. 31, 2014
Dec. 31, 2017
Class of Stock [Line Items]      
Strike price adjustment for dividends (in dollars per share)   $ 0.32  
Stock Option | 2015      
Class of Stock [Line Items]      
Intrinsic value of options exercised     $ 0.8
Stock Option | 2016      
Class of Stock [Line Items]      
Intrinsic value of options exercised     $ 0.4
Stock Option | Mar-11      
Class of Stock [Line Items]      
Risk free rate (as percent)     1.70%
Volatility (as percent)     107.80%
Expected term     3 years 3 months 19 days
Stock Option | Sep-11      
Class of Stock [Line Items]      
Risk free rate (as percent)     1.13%
Dividend yield (as percent)     13.20%
Volatility (as percent)     151.10%
Expected term     4 years 7 months 6 days
Stock Option | Apr-12      
Class of Stock [Line Items]      
Risk free rate (as percent)     1.30%
Dividend yield (as percent)     12.90%
Volatility (as percent)     149.40%
Expected term     4 years 8 months 12 days
Stock Option | May-12      
Class of Stock [Line Items]      
Risk free rate (as percent)     1.05%
Dividend yield (as percent)     11.90%
Volatility (as percent)     148.40%
Expected term     4 years 9 months 18 days
Stock Option | Jul-12      
Class of Stock [Line Items]      
Risk free rate (as percent)     0.75%
Dividend yield (as percent)     11.90%
Volatility (as percent)     147.50%
Expected term     4 years 9 months 18 days
Stock Option | Jan-13      
Class of Stock [Line Items]      
Risk free rate (as percent)     2.00%
Dividend yield (as percent)     8.80%
Volatility (as percent)     56.20%
Expected term     10 years
Stock Option | Feb-13      
Class of Stock [Line Items]      
Risk free rate (as percent)     2.10%
Dividend yield (as percent)     7.80%
Volatility (as percent)     55.50%
Expected term     10 years
Stock Option | Jun-13      
Class of Stock [Line Items]      
Risk free rate (as percent)     2.50%
Dividend yield (as percent)     8.80%
Volatility (as percent)     36.90%
Expected term     10 years
Stock Option | Nov-13      
Class of Stock [Line Items]      
Risk free rate (as percent)     2.80%
Dividend yield (as percent)     6.70%
Volatility (as percent)     32.00%
Expected term     10 years
Stock Option | Aug-14      
Class of Stock [Line Items]      
Risk free rate (as percent)     2.70%
Dividend yield (as percent)     8.60%
Volatility (as percent)     23.40%
Expected term     10 years
Held by the Manager | Stock Option | Prior to 2008      
Class of Stock [Line Items]      
Exercised (in shares)     111,770
Issued to the Manager and subsequently transferred to certain Manager’s employees | Stock Option | Prior to 2008      
Class of Stock [Line Items]      
Exercised (in shares)     61,417
Issued to the Manager and subsequently transferred to certain Manager’s employees | Stock Option | Oct-12      
Class of Stock [Line Items]      
Intrinsic value of options exercised     $ 0.2
Issued to the Manager and subsequently transferred to certain Manager’s employees | Stock Option | Sep-13      
Class of Stock [Line Items]      
Intrinsic value of options exercised     $ 0.9
Issued to the Manager and subsequently transferred to certain Manager’s employees | Stock Option | 2014      
Class of Stock [Line Items]      
Exercised (in shares)     215,853
Intrinsic value of options exercised     $ 4.1
Issued to the Manager and subsequently transferred to certain Manager’s employees | Stock Option | 2016      
Class of Stock [Line Items]      
Options forfeited (in shares)     16,748
Issued to the independent directors | Stock Option | Prior to 2008      
Class of Stock [Line Items]      
Exercised (in shares)     666
Issued to the independent directors | Stock Option | 2014      
Class of Stock [Line Items]      
Exercised (in shares)     333
Stock Option      
Class of Stock [Line Items]      
Issuance of stock options - equitable adjustment (in shares) 178,740    
Share price (in dollars per share) $ 1.00    
Stock Option | Mar-11      
Class of Stock [Line Items]      
Issuance of stock options - equitable adjustment (in shares) 24,354    
Stock Option | Sep-11      
Class of Stock [Line Items]      
Issuance of stock options - equitable adjustment (in shares) 92,963    
Stock Option | Apr-12      
Class of Stock [Line Items]      
Issuance of stock options - equitable adjustment (in shares) 32,105    
Stock Option | May-12      
Class of Stock [Line Items]      
Issuance of stock options - equitable adjustment (in shares) 12,987    
Stock Option | Jul-12      
Class of Stock [Line Items]      
Issuance of stock options - equitable adjustment (in shares) 16,331