Annual report pursuant to Section 13 and 15(d)

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

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EQUITY AND EARNINGS PER SHARE - Outstanding Options Summary (Details) - shares
Dec. 31, 2017
Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Stock options outstanding (in shares) 5,010,576 5,126,906
Issued Prior to 2011    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Stock options outstanding (in shares)   116,330
Issued in 2011 and thereafter    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Stock options outstanding (in shares) 5,010,576 5,010,576
Held by the Manager    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Stock options outstanding (in shares) 3,857,748 5,120,272
Held by the Manager | Issued Prior to 2011    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Stock options outstanding (in shares)   110,029
Held by the Manager | Issued in 2011 and thereafter    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Stock options outstanding (in shares) 3,857,748 5,010,243
Issued to the Manager and subsequently transferred to certain Manager’s employees    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Stock options outstanding (in shares) 1,152,495 6,301
Issued to the Manager and subsequently transferred to certain Manager’s employees | Issued Prior to 2011    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Stock options outstanding (in shares)   6,301
Issued to the Manager and subsequently transferred to certain Manager’s employees | Issued in 2011 and thereafter    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Stock options outstanding (in shares) 1,152,495 0
Issued to the independent directors    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Stock options outstanding (in shares) 333 333
Issued to the independent directors | Issued Prior to 2011    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Stock options outstanding (in shares)   0
Issued to the independent directors | Issued in 2011 and thereafter    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Stock options outstanding (in shares) 333 333