Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Current assets
Cash and cash equivalents	$ 10,479	$ 15,821
Receivables, net	31,377	33,377
Material and supplies	7,471	8,090
Prepaid expenses	3,901	4,093
Other current assets	7,638	7,229
Total current assets	60,866	68,610
Property, plant and equipment, net	598,798	595,997
Intangible assets, net	32,303	32,728
Goodwill	12,104	12,104
Deferred income taxes, net	85,891	92,171
Other assets	4,354	2,311
Total assets	794,316	803,921
Current liabilities
Current portion of long-term debt	3,000	3,000
Accounts payable	47,713	53,506
Accrued expenses	13,310	15,293
Advance billings and customer deposits	15,967	15,013
Other current liabilities	5,948	6,327
Total current liabilities	85,938	93,139
Long-term debt	287,466	281,699
Employee benefit obligations	86,198	105,930
Other liabilities	17,668	18,239
Total liabilities	477,270	499,007
Commitments and contingencies (Note 11)
Stockholders' equity
Common stock, par value of $0.01 per share, 245,000,000 shares authorized and 11,587,963 and 11,513,279 shares issued and outstanding at March 31, 2017 and December 31, 2016, respectively	116	115
Additional paid-in capital	180,429	179,958
Accumulated other comprehensive loss	(22,156)	(35,218)
Retained earnings	158,657	160,059
Total stockholders' equity	317,046	304,914
Total liabilities and stockholders' equity	$ 794,316	$ 803,921