Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Current Assets:
Cash	$ 5,091	$ 3,628
Short-term investments	100,027	150,072
Accounts receivable - net
Trade	98,338	84,768
Other	958	4,891
Inventories of spare parts - net	57,243	59,336
Other current assets	15,302	16,233
Income taxes receivable	346	558
Total current assets	277,305	319,486
Other	27,071	29,120
Property and equipment - net	659,756	596,533
Total assets	964,132	945,139
Current Liabilities:
Accounts payable	17,697	22,404
Accrued liabilities	29,051	28,319
Total current liabilities	46,748	50,723
Long-term debt	346,047	331,074
Deferred income taxes	85,937	81,988
Other long-term liabilities	8,063	8,938
Commitments and contingencies (Note 10)
Shareholders' Equity:
Common stock	285	285
Additional paid-in capital	291,403	291,403
Accumulated other comprehensive loss	(93)	(162)
Retained earnings	184,496	179,644
Total shareholders' equity	477,337	472,416
Total liabilities and shareholders' equity	964,132	945,139
Voting Common Stock
Shareholders' Equity:
Total shareholders' equity	285	285
Non-voting common stock
Shareholders' Equity:
Common stock	1,246	1,246
Total shareholders' equity	$ 1,246	$ 1,246