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Short-term debt (Details) - USD ($) $ in Thousands | Jun. 30, 2019 | Apr. 12, 2019 | Mar. 22, 2019 | Dec. 31, 2018 | Jun. 30, 2018
--- | --- | --- | --- | --- | ---
Short-term Debt [Line Items] |  |  |  |  |
Short-term borrowings | $ 89,983 |  |  | $ 0 | $ 0
Cascade Natural Gas [Member] | Term Loan Agreements |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |
Short-term borrowings |  |  | $ 40,000 |  |
Centennial Energy Holdings, Inc. [Member] | Term Loan Agreements |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |
Short-term borrowings |  | $ 50,000 |  |  |

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- 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. + References No definition available. + Details
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- Details
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