Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Current assets
Cash and cash equivalents	$ 26,155	$ 30,312
Receivables, net	29,120	32,736
Material and supplies	8,603	8,499
Prepaid expenses	5,580	4,068
Other current assets	3,184	2,102
Total current assets	72,642	77,717
Property, plant and equipment, net	589,551	579,107
Intangible assets, net	33,779	34,828
Goodwill	12,104	12,104
Deferred income taxes, net	88,331	89,896
Other assets	6,193	6,043
Total assets	802,600	799,695
Current liabilities
Current portion of long-term debt	3,000	3,000
Accounts payable	50,546	44,841
Accrued expenses	16,561	14,491
Advance billings and customer deposits	15,958	17,551
Other current liabilities	6,305	5,932
Total current liabilities	92,370	85,815
Long-term debt	282,161	283,046
Employee benefit obligations	100,207	104,597
Other liabilities	17,468	18,538
Total liabilities	492,206	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 June 30, 2016 and December 31, 2015, respectively	115	115
Additional paid-in capital	178,809	178,019
Accumulated other comprehensive loss	(29,082)	(29,388)
Retained earnings	160,552	158,953
Total stockholders' equity	310,394	307,699
Total liabilities and stockholders' equity	$ 802,600	$ 799,695