Investment in ATC and ATC Holdco (Details-2) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
ATC [Member]
Schedule Of Equity Method Investments [Line Items]
Operating revenues	$ 177,715	$ 165,429
Operating expenses	(90,387)	(84,893)
Other income, net	260	111
Interest expense, net	(29,118)	(27,762)
Earnings before members' income taxes	58,470	52,885
ATC [Member]
Related Party Transaction [Line Items]
Related party expenses	7,600	$ 7,200
Due from related parties	$ 100		$ 100

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

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

+ References

No definition available.

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

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No definition available.

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For an unclassified balance sheet, amounts due from related parties including affiliates, employees, joint ventures, officers and stockholders, immediate families thereof, and pension funds.

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

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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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Expenses recognized resulting from transactions (excluding transactions that are eliminated in consolidated or combined financial statements) with related party.

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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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No definition available.

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