Selected Quarterly Financial Data (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended																12 Months Ended
	Dec. 31, 2013		Sep. 30, 2013		Jun. 30, 2013		Mar. 31, 2013		Dec. 31, 2012		Sep. 30, 2012		Jun. 30, 2012		Mar. 31, 2012		Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Selected Quarterly Financial Information [Abstract]
Operating revenues	$ 447,676		$ 335,875		$ 352,048		$ 482,906		$ 410,528		$ 340,632		$ 343,585		$ 452,257		$ 1,618,505	$ 1,547,002	$ 1,619,780
Operating expenses	381,356	[1]	300,606	[1]	294,306	[1]	397,844	[1]	369,481	[1]	314,023	[1]	297,565	[1]	375,863	[1]	1,374,112	1,356,932	1,391,776
Income from operations	66,320	[1]	35,269	[1]	57,742	[1]	85,062	[1]	41,047	[1]	26,609	[1]	46,020	[1]	76,394	[1]	244,393	190,070	228,004
Net income	31,532		11,931		25,730		43,101		16,093		5,962		18,532		38,213		112,294	78,800	103,539
Net loss (income) attributable to noncontrolling interests	134		(518)		(73)		(760)		(235)		(176)		(354)		175
Net income attributable to Avista Corporation shareholders	$ 31,666		$ 11,413		$ 25,657		$ 42,341		$ 15,858		$ 5,786		$ 18,178		$ 38,388		$ 111,077	$ 78,210	$ 100,224
Weighted average, basic	60,037		59,994		59,937		59,866		59,774		59,047		58,702		58,581		59,960	59,028	57,872
Weighted average, diluted	60,087		60,032		59,962		59,898		59,826		59,123		58,924		58,950		59,997	59,201	58,092
Diluted (usd per share)	$ 0.53		$ 0.19		$ 0.43		$ 0.71		$ 0.26		$ 0.10		$ 0.31		$ 0.65		$ 1.85	$ 1.32	$ 1.72

[1] Three Months Ended March 31 June 30 September 30 December 312013 Operating revenues$482,906 $352,048 $335,875 $447,676Operating expenses397,844 294,306 300,606 381,356Income from operations$85,062 $57,742 $35,269 $66,320Net income$43,101 $25,730 $11,931 $31,532Net loss (income) attributable to noncontrolling interests(760) (73) (518) 134Net income attributable to Avista Corporation shareholders$42,341 $25,657 $11,413 $31,666Outstanding common stock: Weighted average, basic59,866 59,937 59,994 60,037Weighted average, diluted59,898 59,962 60,032 60,087Earnings per common share attributable to Avista Corporation shareholders, diluted$0.71 $0.43 $0.19 $0.532012 Operating revenues$452,257 $343,585 $340,632 $410,528Operating expenses375,863 297,565 314,023 369,481Income from operations$76,394 $46,020 $26,609 $41,047Net income$38,213 $18,532 $5,962 $16,093Net loss (income) attributable to noncontrolling interests175 (354) (176) (235)Net income attributable to Avista Corporation shareholders$38,388 $18,178 $5,786 $15,858Outstanding common stock: Weighted average, basic58,581 58,702 59,047 59,774Weighted average, diluted58,950 58,924 59,123 59,826Earnings per common share attributable to Avista Corporation shareholders, diluted$0.65 $0.31 $0.10 $0.26