Condensed Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Current assets
Cash and cash equivalents	$ 58,420	$ 66,993
Receivables, net	33,344	34,082
Material and supplies	11,802	11,352
Prepaid expenses	6,786	5,161
Deferred income taxes, current	5,727	5,727
Other current assets	2,062	2,181
Total current assets	118,141	125,496
Property, plant and equipment, net	506,827	507,197
Intangible assets, net	37,337	39,075
Goodwill	1,415	1,569
Deferred income taxes	98,520	102,680
Other assets	11,780	9,075
Total assets	774,020	785,092
Current liabilities
Current portion of long-term debt	2,362	3,000
Accounts payable	29,107	36,351
Accrued expenses	15,270	20,537
Advance billings and customer deposits	16,219	15,185
Other current liabilities	4,000	3,961
Total current liabilities	66,958	79,034
Long-term debt	292,818	292,410
Employee benefit obligations	125,851	132,004
Other liabilities	4,734	4,784
Total liabilities	490,361	508,232
Commitments and contingencies (Note 12)
Stockholders' equity
Common stock, par value of $0.01 per share, 245,000,000 shares authorized and 10,336,484 and 10,291,897 shares issued and outstanding at June 30, 2013 and December 31, 2012, respectively	103	103
Additional paid-in capital	166,700	165,941
Accumulated other comprehensive loss	(28,208)	(28,450)
Retained earnings	145,064	139,266
Total stockholders' equity	283,659	276,860
Total liabilities and stockholders' equity	$ 774,020	$ 785,092