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Investment in ATC (Details-2) - ATC [Member] - USD ($) $ in Thousands | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2016 | Jun. 30, 2015 | Jun. 30, 2016 | Jun. 30, 2015
Schedule Of Equity Method Investments [Line Items] |  |  |  |
Operating revenues | $ 154,225 | $ 165,171 | $ 318,465 | $ 317,528
Operating expenses | (81,698) | (80,326) | (160,763) | (160,277)
Other income (expense), net | 1,308 | (81) | 1,435 | (19)
Interest expense, net | (24,882) | (24,172) | (49,090) | (48,655)
Earnings before members' income taxes | $ 48,953 | $ 60,592 | $ 110,047 | $ 108,577

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