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Jointly owned facilities | 12 Months Ended
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Dec. 31, 2017
Regulated Operations [Abstract] |
Jointly owned facilities | Jointly Owned Facilities The consolidated financial statements include the Company's ownership interests in the assets, liabilities and expenses of the Big Stone Station, Coyote Station and Wygen III. Each owner of the stations is responsible for financing its investment in the jointly owned facilities. The Company's share of the stations operating expenses was reflected in the appropriate categories of operating expenses (fuel, operation and maintenance and taxes, other than income) in the Consolidated Statements of Income. At December 31, the Company's share of the cost of utility plant in service and related accumulated depreciation for the stations was as follows:
| 2017 |  | 2016 |
| (In thousands)
Big Stone Station: |  |
Utility plant in service | $ | 158,084 |  | $ | 157,144 |
Less accumulated depreciation | 51,740 |  | 49,568 |
| $ | 106,344 |  | $ | 107,576 |
Coyote Station: |  |  |  |
Utility plant in service | $ | 155,287 |  | $ | 156,334 |
Less accumulated depreciation | 103,897 |  | 105,928 |
| $ | 51,390 |  | $ | 50,406 |
Wygen III: |  |  |  |
Utility plant in service | $ | 65,065 |  | $ | 66,251 |
Less accumulated depreciation | 7,652 |  | 7,550 |
| $ | 57,413 |  | $ | 58,701 |

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