Quarterly Results of Operations (Schedule of Quarterly Financial Information ) (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
Net Operating Revenue:
Net operating revenue	$ 46,802	$ 43,057	$ 47,115	$ 46,589	$ 52,613	$ 49,052	$ 51,169	$ 49,453	$ 183,563	$ 202,287
Operating income (loss)	(2,414)	(6,974)	22,855	(3,928)	(17,946)	(1,302)	(1,367)	(6,217)	9,539	(26,832)
Net Income (Loss)	$ (1,096)	$ (4,005)	$ 16,528	$ (2,135)	$ (19,637)	$ (1,036)	$ (534)	$ (4,014)	$ 9,292	$ (25,221)
Net income (loss) per share
Basic and diluted	$ (0.05)	$ (0.19)	$ 0.77	$ (0.10)	$ (0.91)	$ (0.05)	$ (0.03)	$ (0.19)	$ 0.43	$ (1.17)