Annual report pursuant to Section 13 and 15(d)

Quarterly Financial Information - Summary of Quarterly Results of Operations (Detail)

v3.8.0.1
Quarterly Financial Information - Summary of Quarterly Results of Operations (Detail) - USD ($)
$ / shares in Units, $ in Thousands
3 Months Ended 12 Months Ended
Dec. 31, 2017
Sep. 30, 2017
Jun. 30, 2017
Mar. 31, 2017
Dec. 31, 2016
Sep. 30, 2016
Jun. 30, 2016
Mar. 31, 2016
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Quarterly Financial Information Disclosure [Abstract]                      
Operating revenues $ 25,253 $ 24,365 $ 22,867 $ 22,314 $ 22,009 $ 21,589 $ 21,247 $ 21,527 $ 94,799 $ 86,372 $ 83,766
Operating expenses (20,405) (15,867) (14,357) (17,708) (13,733) (15,172) (13,433) (13,257) (68,337) (55,595) (50,965)
Other expense, net (6,311) (6,115) (7,849) (250) (5,981) (6,490) (6,931) (7,417) (20,525) (26,819) (29,205)
Net income (1,463) 2,383 661 4,356 2,295 (73) 883 853 5,937 3,958 3,596
Dividends attributable to preferred and senior common stock (2,802) (2,767) (2,686) (2,621) (2,607) (2,256) (1,514) (1,279)   (7,656) (5,101)
Net loss attributable to common stockholders $ (4,265) $ (384) $ (2,025) $ 1,735 $ (312) $ (2,329) $ (631) $ (426) $ (4,939) $ (3,698) $ (1,505)
Net income (loss) available (attributable to common stockholders - basic & diluted (in dollars per share) $ (0.17) $ (0.01) $ (0.08) $ 0.07 $ (0.01) $ (0.10) $ (0.03) $ (0.02) $ (0.19) $ (0.16) $ (0.07)