Consolidated Statements of Operations - USD ($) shares in Thousands, $ 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
Income Statement [Abstract]
Operating revenues, net	$ 148,336	$ 150,167	$ 146,424	$ 134,618	$ 144,853	$ 158,093	$ 167,136	$ 164,016	$ 579,545	$ 634,098	$ 804,228
Expenses:
Direct expenses									546,699	592,550	687,050
Selling, general and administrative expenses									53,817	44,418	46,422
Total operating expenses									600,516	636,968	733,472
Loss (gain) on disposition of assets, net	(287)	(4)	(7)	0	504	85	(4,298)	359	298	(3,350)	339
Impairments of assets									368	407	0
Equity in loss (profit) of unconsolidated affiliate									385	(151)	306
Operating income									(22,022)	224	70,111
Interest expense									32,183	30,644	29,066
Other income, net									(2,764)	(3,271)	(2,211)
Total expenses									29,419	27,373	26,855
(Loss) earnings before income taxes	(20,319)	(4,899)	(3,150)	(23,073)	(12,012)	(7,766)	117	(7,488)	(51,441)	(27,149)	43,256
Income tax (benefit) expense									(58,973)	(469)	16,332
Net earnings (loss)	$ 29,330	$ (3,277)	$ (3,273)	$ (15,248)	$ (17,058)	$ (4,967)	$ 4,277	$ (8,932)	$ 7,532	$ (26,680)	$ 26,924
Earnings (loss) per share:
Basic (USD per share)	$ 1.87	$ (0.21)	$ (0.21)	$ (0.97)	$ (1.08)	$ (0.32)	$ 0.27	$ (0.57)	$ 0.48	$ (1.70)	$ 1.73
Diluted (USD per share)	$ 1.87	$ (0.21)	$ (0.21)	$ (0.97)	$ (1.08)	$ (0.32)	$ 0.27	$ (0.57)	$ 0.48	$ (1.70)	$ 1.72
Weighted average shares outstanding:
Basic (shares)									15,762	15,663	15,566
Diluted (shares)									15,762	15,663	15,642