Condensed Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Current assets
Cash and cash equivalents	$ 45,114	$ 66,993
Receivables, net	36,706	34,082
Material and supplies	15,268	11,352
Prepaid expenses	5,344	5,161
Deferred income taxes	5,892	5,727
Other current assets	2,751	2,181
Total current assets	111,075	125,496
Property, plant and equipment, net	517,874	507,197
Intangible assets, net	41,052	39,075
Goodwill	11,783	1,569
Deferred income taxes	94,908	102,680
Other assets	12,315	9,075
Total assets	789,007	785,092
Current liabilities
Current portion of long-term debt	3,000	3,000
Accounts payable	39,102	36,351
Accrued expenses	16,227	20,537
Advance billings and customer deposits	16,159	15,185
Other current liabilities	5,387	3,961
Total current liabilities	79,875	79,034
Long-term debt	292,248	292,410
Employee benefit obligations	121,014	132,004
Other liabilities	9,309	4,784
Total liabilities	502,446	508,232
Commitments and contingencies (Note 12)
Stockholders' equity
Common stock, par value of $0.01 per share, 245,000,000 shares authorized and 10,338,737 and 10,291,897 shares issued and outstanding at September 30, 2013 and December 31, 2012, respectively	103	103
Additional paid-in capital	167,401	165,941
Accumulated other comprehensive loss	(28,068)	(28,450)
Retained earnings	147,125	139,266
Total stockholders' equity	286,561	276,860
Total liabilities and stockholders' equity	$ 789,007	$ 785,092