Annual report pursuant to Section 13 and 15(d)

QUARTERLY FINANCIAL INFORMATION (UNAUDITED) (Details)

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QUARTERLY FINANCIAL INFORMATION (UNAUDITED) (Details) - USD ($)
$ / shares in Units, $ in Thousands
3 Months Ended 12 Months Ended
Dec. 31, 2019
Sep. 30, 2019
Jun. 30, 2019
Mar. 31, 2019
Dec. 31, 2018
Sep. 30, 2018
Jun. 30, 2018
Mar. 31, 2018
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]                      
Revenues $ 60,377 $ 58,909 $ 55,480 $ 51,293 $ 52,016 $ 54,610 $ 57,728 $ 57,322 $ 226,059 $ 221,676 $ 231,321
Operating income (loss) 710 1,687 (1,823) (3,852) (5,629) 41,571 (9,523) 1,651 (3,278) 28,070 (136,464)
Net income (loss) (811) (2,059) 4,874 (6,085) (5,948) 31,279 (10,516) (1,357) $ (4,081) $ 13,458 $ (28,615)
Net income (loss) attributable to common shares $ (680) $ (1,910) $ 4,940 $ (5,943) $ (5,794) $ 31,289 $ (10,379) $ (1,194)      
Earnings (loss) per common share - basic (in dollars per share) $ (0.03) $ (0.09) $ 0.22 $ (0.28) $ (0.27) $ 1.44 $ (0.49) $ (0.06) $ (0.17) $ 0.64 $ (1.36)
Earnings (loss) per common share - diluted (in dollars per share) $ (0.03) $ (0.09) $ 0.22 $ (0.28) $ (0.27) $ 1.44 $ (0.49) $ (0.06) $ (0.17) $ 0.64 $ (1.36)