Jointly Owned Electric Facilities (Tables)

12 Months Ended

Dec. 31, 2018

Jointly Owned Utility Plant, Net Ownership Amount [Abstract]

Schedule Of Jointly Owned Electric Facilities

	2018			2017
Utility plant in service	$	384,431		$	379,970
Accumulated depreciation	(261,997		)	(255,604		)

See Note 9 for further discussion of AROs.

While the obligations and liabilities with respect to Colstrip are to be shared among the co-owners on a pro rata basis, many of the environmental liabilities are joint and several under the law, so that if any co-owner failed to pay its share of such liability, the other co-owners (or any one of them) could be required to pay the defaulting co-owner‘s share (or the entire liability).