Investment in ATC (Details-2) (ATC [Member], USD $) In Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
ATC [Member]
Equity method investment summarized income statement [Line Items]
Operating revenues	$ 142,741	$ 136,889	$ 420,562	$ 414,046
Operating expenses	(66,413)	(59,732)	(192,491)	(185,067)
Other expense, net	(173)	(609)	(665)	(1,428)
Interest expense, net	(19,517)	(21,530)	(60,893)	(63,361)
Earnings before members' income taxes	$ 56,638	$ 55,018	$ 166,513	$ 164,190

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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The amount of interest reported by an equity method investment of the entity.

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- Definition

The amount of net income or net loss before taxes reported by an equity method investment of the entity.

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The amount of other expenses reported by an equity method investment of the entity.

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The amount of the cost of sales reported by an equity method investment of the entity.

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- Definition

The amount of revenue from sale of goods and services reduced by sales returns, allowances, and discounts reported by an equity method investment of the entity.

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