Annual report pursuant to Section 13 and 15(d)

QUARTERLY FINANCIAL INFORMATION (UNAUDITED) (Details)

v3.7.0.1
QUARTERLY FINANCIAL INFORMATION (UNAUDITED) (Details) - USD ($)
$ / shares in Units, $ in Thousands
3 Months Ended 12 Months Ended
Dec. 31, 2016
Sep. 30, 2016
Jun. 30, 2016
Mar. 31, 2016
Dec. 31, 2015
Sep. 30, 2015
Jun. 30, 2015
Mar. 31, 2015
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Quarterly Financial Information Disclosure [Abstract]                      
Operating revenues $ 56,289 $ 65,006 $ 63,351 $ 62,582 $ 73,943 $ 69,741 $ 70,738 $ 67,415 $ 247,228 $ 281,837 $ 331,222
Operating income (loss) (1,421) 2,366 (3,509) (805) 4,783 5,123 8,535 5,853 (3,369) 24,294 42,651
Net income (loss) (5,648) (802) (4,510) (3,950) (3,620) 653 11,105 (239) $ (14,910) 7,899 $ 17,021
Net income attributable to common shares $ (5,538) $ (560) $ 1,938 $ (3,818) $ (3,447) $ 861 $ 11,333 $ (42)   $ 8,705  
Earnings (loss) per common share, basic (in dollars per share) $ (0.27) $ (0.03) $ 0.09 $ (0.19) $ (0.17) $ 0.04 $ 0.55 $ 0.00 $ (0.39) $ 0.42 $ 0.84
Earnings (loss) per common share, diluted (in dollars per share) $ (0.27) $ (0.03) $ 0.09 $ (0.19) $ (0.17) $ 0.04 $ 0.55 $ 0.00 $ (0.39) $ 0.42 $ 0.84