Jointly Owned Electric Facilities

12 Months Ended

Dec. 31, 2012

Jointly Owned Utility Plant, Net Ownership Amount [Abstract]

Jointly Owned Electric Facilities

JOINTLY OWNED ELECTRIC FACILITIES

The Company has a 15 percent ownership interest in a twin-unit coal-fired generating facility, the Colstrip Generating Project (Colstrip) located in southeastern Montana, and provides financing for its ownership interest in the project. The Company’s share of related fuel costs as well as operating expenses for plant in service are included in the corresponding accounts in the Consolidated Statements of Income. The Company’s share of utility plant in service for Colstrip and accumulated depreciation were as follows as of December 31 (dollars in thousands):

	2012			2011
Utility plant in service	$	344,958		$	342,539
Accumulated depreciation	(234,126		)	(225,746		)