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SHAREHOLDERS' EQUITY AND PARTNERS' CAPITAL - At-the-Market Equity Program (Details) - USD ($)
 12 Months Ended 82 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2019
Mar. 01, 2013
Class Of Stock [Line Items]          
Common stock offering, maximum aggregate price (up to)         $ 300,000,000
Commission to sales agent (as a percent)         2.00%
Issuance of common stock and restricted common stock (shares) 915,226 727,812 348,809    
Common stock offering, maximum remaining aggregate price $ 88,507,000     $ 88,507,000  
Common Stock          
Class Of Stock [Line Items]          
Gross proceeds from issuance of common stock 211,493,000        
Net proceeds from issuance of common stock $ 209,596,000        
Issuance of common stock and restricted common stock (shares)       8,419,298  
At The Market Stock Sales          
Class Of Stock [Line Items]          
Proceeds from sale of common stock weighted average price per share (USD per share) $ 25.12