Consolidated Statements Of Equity And Redeemable Noncontrolling Interests - USD ($) $ in Thousands	Total	Common Stock [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Retained Earnings [Member]	Noncontrolling Interests [Member]
Beginning Balance (in shares) at Dec. 31, 2015		62,312,651
Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Shares issued		1,391,644
Ending Balance (in shares) at Jun. 30, 2016		63,704,295
Beginning Balance at Dec. 31, 2015		$ 1,004,336	$ (6,650)	$ 530,940
Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Equity compensation expense		3,708
Issuance of common stock, net of issuance costs		47,173
Payment of minimum tax withholdings for share-based payment awards		(3,027)
Other comprehensive income (loss)	$ (1,089)		(1,089)
Net income attributable to Avista Corporation shareholders	84,903			84,903
Cash dividends paid (common stock)				(43,267)
Ending Balance at Jun. 30, 2016	$ 1,617,027	$ 1,052,190	(7,739)	572,576
Beginning Balance Noncontrolling Interest at Dec. 31, 2015					$ (339)
Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Net income (loss) attributable to noncontrolling interests					49
Ending Balance Noncontrolling Interest at Jun. 30, 2016					(290)
Beginning Balance (in shares) at Dec. 31, 2015		62,312,651
Ending Balance (in shares) at Dec. 31, 2016	64,187,934	64,187,934
Beginning Balance at Dec. 31, 2015		$ 1,004,336	(6,650)	530,940
Ending Balance at Dec. 31, 2016	$ 1,648,727	$ 1,075,281	(7,568)	581,014
Beginning Balance Noncontrolling Interest at Dec. 31, 2015					(339)
Ending Balance Noncontrolling Interest at Dec. 31, 2016	251				(251)
Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Total equity	1,616,737
Total equity	$ 1,648,476
Shares issued		221,049
Ending Balance (in shares) at Jun. 30, 2017	64,408,983	64,408,983
Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Equity compensation expense		$ 2,559
Issuance of common stock, net of issuance costs		1,247
Payment of minimum tax withholdings for share-based payment awards		(3,420)
Other comprehensive income (loss)	$ 366		366
Net income attributable to Avista Corporation shareholders	83,887			83,887
Cash dividends paid (common stock)				(46,193)
Ending Balance at Jun. 30, 2017	1,687,173	$ 1,075,667	$ (7,202)	$ 618,708
Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Net income (loss) attributable to noncontrolling interests					(28)
Ending Balance Noncontrolling Interest at Jun. 30, 2017	279				$ (279)
Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Total equity	$ 1,686,894