Quarterly report pursuant to Section 13 or 15(d)

SUBSEQUENT EVENTS (Details)

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SUBSEQUENT EVENTS (Details) - USD ($)
$ / shares in Units, $ in Thousands
 9 Months Ended 12 Months Ended
Nov. 07, 2018
Aug. 02, 2018
May 02, 2018
Mar. 06, 2018
Sep. 30, 2018
Dec. 31, 2017
Subsequent Event [Line Items]            
Dividends declared         $ 4,185  
Series B preferred stock            
Subsequent Event [Line Items]            
Dividends declared per share of preferred stock (in dollars per share)   $ 0.609375 $ 0.609375 $ 0.609375    
Preferred stock, dividend rate (as percent)   9.75% 9.75% 9.75% 9.75% 9.75%
Series C preferred stock            
Subsequent Event [Line Items]            
Dividends declared per share of preferred stock (in dollars per share)   $ 0.503125 $ 0.503125 $ 0.503125    
Preferred stock, dividend rate (as percent)   8.05% 8.05% 8.05% 8.05% 8.05%
Series D preferred stock            
Subsequent Event [Line Items]            
Dividends declared per share of preferred stock (in dollars per share)   $ 0.523438 $ 0.523438 $ 0.523438    
Preferred stock, dividend rate (as percent)   8.375% 8.375% 8.375% 8.375% 8.375%
Subsequent event            
Subsequent Event [Line Items]            
Dividends declared $ 1,400          
Subsequent event | Series B preferred stock            
Subsequent Event [Line Items]            
Dividends declared per share of preferred stock (in dollars per share) $ 0.609375          
Preferred stock, dividend rate (as percent) 9.75%          
Subsequent event | Series C preferred stock            
Subsequent Event [Line Items]            
Dividends declared per share of preferred stock (in dollars per share) $ 0.503125          
Preferred stock, dividend rate (as percent) 8.05%          
Subsequent event | Series D preferred stock            
Subsequent Event [Line Items]            
Dividends declared per share of preferred stock (in dollars per share) $ 0.523438          
Preferred stock, dividend rate (as percent) 8.375%