Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Current assets
Cash and cash equivalents	$ 25,854	$ 15,821
Receivables, net	28,030	33,377
Material and supplies	7,127	8,090
Prepaid expenses	5,898	4,093
Other current assets	7,292	7,229
Total current assets	74,201	68,610
Property, plant and equipment, net	601,332	595,997
Intangible assets, net	31,877	32,728
Goodwill	12,104	12,104
Deferred income taxes, net	88,528	92,171
Other assets	2,462	2,311
Total assets	810,504	803,921
Current liabilities
Current portion of long-term debt	10,250	3,000
Accounts payable	47,920	53,506
Accrued expenses	10,433	15,293
Advance billings and customer deposits	15,095	15,013
Other current liabilities	6,822	6,327
Total current liabilities	90,520	93,139
Long-term debt	303,636	281,699
Employee benefit obligations	85,367	105,930
Other liabilities	17,324	18,239
Total liabilities	496,847	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 June 30, 2017 and December 31, 2016, respectively	116	115
Additional paid-in capital	181,135	179,958
Accumulated other comprehensive loss	(22,774)	(35,218)
Retained earnings	155,180	160,059
Total stockholders' equity	313,657	304,914
Total liabilities and stockholders' equity	$ 810,504	$ 803,921