Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Current assets
Cash and cash equivalents	$ 39,885	$ 49,551
Receivables, net	32,662	34,521
Material and supplies	9,337	15,939
Prepaid expenses	3,598	3,724
Deferred income taxes	6,840	8,146
Other current assets	3,481	2,851
Total current assets	95,803	114,732
Property, plant and equipment, net	565,956	524,375
Intangible assets, net	37,328	40,225
Goodwill	12,104	12,104
Deferred income taxes	81,626	75,274
Other assets	9,151	11,305
Total assets	801,968	778,015
Current liabilities
Current portion of long-term debt	3,000	3,000
Accounts payable	50,499	40,228
Accrued expenses	19,399	18,787
Advance billings and customer deposits	14,686	16,122
Other current liabilities	6,790	6,412
Total current liabilities	94,374	84,549
Long-term debt	289,423	291,679
Employee benefit obligations	99,366	80,321
Other liabilities	14,271	8,454
Total liabilities	497,434	465,003
Commitments and contingencies (Note 14)
Stockholders' equity
Common stock, par value of $0.01 per share, 245,000,000 shares authorized and 10,673,292 and 10,495,856 shares issued and outstanding at December 31, 2014 and 2013, respectively	107	105
Additional paid-in capital	170,521	167,869
Accumulated other comprehensive loss	(23,947)	(4,716)
Retained earnings	157,853	149,754
Total stockholders' equity	304,534	313,012
Total liabilities and stockholders' equity	$ 801,968	$ 778,015