CONDENSED CONSOLIDATED BALANCE SHEETS (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Current Assets:
Cash	$ 9,336	$ 934
Short-term investments	141,473	85,916
Accounts receivable - net
Trade	169,635	172,538
Other	2,047	1,182
Inventories of spare parts - net	72,193	71,137
Prepaid expenses	9,660	8,357
Deferred income taxes	12,723	12,723
Income taxes receivable	1,871	1,871
Total current assets	418,938	354,658
Property and equipment - net	834,408	785,472
Restricted investments	14,685	14,685
Other assets	24,504	18,508
Total assets	1,292,535	1,173,323
Current Liabilities:
Accounts payable	52,818	36,874
Short-term debt	7,429
Accrued and other current liabilities	38,489	54,531
Total current liabilities	98,736	91,405
Long-term debt	500,000	379,000
Deferred income taxes	122,804	127,357
Other long-term liabilities	15,830	15,596
Commitments and contingencies (Note 9)
Shareholders' Equity:
Additional paid-in capital	297,444	296,932
Accumulated other comprehensive loss	(16)	(24)
Retained earnings	256,188	261,509
Total shareholders' equity	555,165	559,965
Total liabilities and shareholders' equity	1,292,535	1,173,323
Voting Common Stock [Member]
Shareholders' Equity:
Common stock	291	291
Total shareholders' equity	291	291
Non-Voting Common Stock [Member]
Shareholders' Equity:
Common stock	1,258	1,257
Total shareholders' equity	$ 1,258	$ 1,257