Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Current assets
Cash and cash equivalents	$ 20,852	$ 30,312
Receivables, net	31,490	32,736
Material and supplies	9,916	8,499
Prepaid expenses	4,244	4,068
Other current assets	3,175	2,102
Total current assets	69,677	77,717
Property, plant and equipment, net	582,271	579,107
Intangible assets, net	34,304	34,828
Goodwill	12,104	12,104
Deferred income taxes, net	89,561	89,896
Other assets	6,452	6,043
Total assets	794,369	799,695
Current liabilities
Current portion of long-term debt	3,000	3,000
Accounts payable	43,544	44,841
Accrued expenses	13,202	14,491
Advance billings and customer deposits	18,143	17,551
Other current liabilities	5,023	5,932
Total current liabilities	82,912	85,815
Long-term debt	282,775	283,046
Employee benefit obligations	102,503	104,597
Other liabilities	17,946	18,538
Total liabilities	486,136	491,996
Stockholders' equity
Common stock, par value of $0.01 per share, 245,000,000 shares authorized and 11,511,591 and 11,466,398 shares issued and outstanding at March 31, 2016 and December 31, 2015, respectively	115	115
Additional paid-in capital	178,246	178,019
Accumulated other comprehensive loss	(29,235)	(29,388)
Retained earnings	159,107	158,953
Total stockholders' equity	308,233	307,699
Total liabilities and stockholders' equity	$ 794,369	$ 799,695