Note 20 - Quarterly Results of Operations (Unaudited) - Quarterly Financial Information (Details) - USD ($) $ / shares in Units, shares in Thousands, $ 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
Operating revenues	$ 123,497	$ 128,994	$ 133,000	$ 128,686	$ 138,176	$ 140,325	$ 135,302	$ 119,458	$ 514,177	$ 533,261	$ 437,838
Operating expenses and costs	141,381	121,461	119,789	118,999	123,500	127,172	125,285	115,702	501,630	491,659	425,158
Operating income (loss)	(17,884)	7,533	13,211	9,687	14,676	13,153	10,017	3,756	12,547	41,602	12,680
Non-operating income (loss)	2,457	490	(197)	3,472	(4,704)	935	632	(879)	6,222	(4,016)	5,853
Interest expense	(2,377)	(2,178)	(2,059)	(2,040)	(2,019)	(1,711)	(1,355)	(1,160)	(8,654)	(6,245)	(3,902)
Income tax (expense) benefit	4,168	(1,264)	(2,301)	(2,818)	(1,883)	(3,129)	(2,005)	(330)	(2,215)	(7,347)	24,268
Net income	$ (13,636)	$ 4,581	$ 8,654	$ 8,301	$ 6,070	$ 9,248	$ 7,289	$ 1,387	$ 7,900	$ 23,994	$ 38,899
Basic (in dollars per share)	$ (2.37)	$ 0.80	$ 1.47	$ 1.40	$ 1.02	$ 1.53	$ 1.18	$ 0.22	$ 1.35	$ 3.94	$ 6.14
Diluted (in dollars per share)	$ (2.37)	$ 0.79	$ 1.45	$ 1.39	$ 1.01	$ 1.52	$ 1.17	$ 0.22	$ 1.34	$ 3.90	$ 6.08
Basic (in shares)	5,751	5,756	5,901	5,921	5,975	6,034	6,159	6,168	5,832	6,083	6,331
Diluted (in shares)	5,751	5,799	5,949	5,985	6,029	6,088	6,229	6,264	5,880	6,159	6,398