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STOCKHOLDERS' EQUITY - Common Stock (Details) - USD ($)
$ in Thousands
 12 Months Ended
May 11, 2016
Mar. 08, 2016
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Class of Stock [Line Items]          
Net proceeds from issuance of common stock     $ 0 $ 175,078 $ 0
Common Stock          
Class of Stock [Line Items]          
Issuance of stock shares (in shares) 5,250,000 4,850,000      
Net proceeds from issuance of common stock $ 100,000 $ 66,500      
Common Stock | Over Allotment Option          
Class of Stock [Line Items]          
Issuance of stock shares (in shares)   727,500      
Net proceeds from issuance of common stock   $ 10,500      
Underwriters option period   30 days