Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Current assets
Cash and cash equivalents	$ 15,821	$ 30,312
Receivables, net	33,377	32,736
Material and supplies	8,090	8,499
Prepaid expenses	4,093	4,068
Other current assets	7,229	2,102
Total current assets	68,610	77,717
Property, plant and equipment, net	595,997	579,107
Intangible assets, net	32,728	34,828
Goodwill	12,104	12,104
Deferred income taxes, net	92,171	89,896
Other assets	2,311	6,043
Total assets	803,921	799,695
Current liabilities
Current portion of long-term debt	3,000	3,000
Accounts payable	53,506	44,841
Accrued expenses	15,293	14,491
Advance billings and customer deposits	15,013	17,551
Other current liabilities	6,327	5,932
Total current liabilities	93,139	85,815
Long-term debt	281,699	283,046
Employee benefit obligations	105,930	104,597
Other liabilities	18,239	18,538
Total liabilities	499,007	491,996
Commitments and contingencies (Note 13)
Stockholders' equity
Common stock, par value of $0.01 per share, 245,000,000 shares authorized and 11,513,279 and 11,466,398 shares issued and outstanding at December 31, 2016 and 2015, respectively	115	115
Additional paid-in capital	179,958	178,019
Accumulated other comprehensive loss	(35,218)	(29,388)
Retained earnings	160,059	158,953
Total stockholders' equity	304,914	307,699
Total liabilities and stockholders' equity	$ 803,921	$ 799,695