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Long-term debt Issued (Details 2) - USD ($) $ in Thousands | Jun. 30, 2019 | Jun. 13, 2019 | Jun. 07, 2019 | Apr. 04, 2019 | Dec. 31, 2018 | Apr. 25, 2017
--- | --- | --- | --- | --- | --- | ---
Long-term debt issued [Line Items] |  |  |  |  |  |
Long-term debt | $ 2,379,806 |  |  |  | $ 2,108,695 |
Senior Notes |  |  |  |  |  |
Long-term debt issued [Line Items] |  |  |  |  |  |
Long-term debt | $ 1,656,000 |  |  |  | 1,381,000 |
Weighted Average Interest Rate | 4.52% |  |  |  |  |
Credit Agreements |  |  |  |  |  |
Long-term debt issued [Line Items] |  |  |  |  |  |
Long-term debt | $ 11,075 |  |  |  | $ 110,100 |
Weighted Average Interest Rate | 5.50% |  |  |  |  |
Centennial Energy Holdings, Inc. [Member] | Senior Notes |  |  |  |  |  |
Long-term debt issued [Line Items] |  |  |  |  |  |
Long-term debt |  |  |  | $ 150,000 |  |
Weighted Average Interest Rate |  |  |  | 4.60% |  |
Cascade Natural Gas [Member] | Senior Notes |  |  |  |  |  |
Long-term debt issued [Line Items] |  |  |  |  |  |
Long-term debt |  | $ 75,000 |  |  |  |
Weighted Average Interest Rate |  | 3.93% |  |  |  |
Cascade Natural Gas [Member] | Credit Agreements |  |  |  |  |  |
Long-term debt issued [Line Items] |  |  |  |  |  |
Long-term debt |  |  | $ 100,000 |  |  | $ 75,000
Intermountain Gas Company [Member] | Senior Notes |  |  |  |  |  |
Long-term debt issued [Line Items] |  |  |  |  |  |
Long-term debt |  | $ 50,000 |  |  |  |
Weighted Average Interest Rate |  | 3.92% |  |  |  |

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