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		895,408
Ending Balance (in shares) at Mar. 31, 2016		63,208,059
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		1,967
Issuance of common stock, net of issuance costs		27,150
Payment of minimum tax withholdings for share-based payment awards		(3,027)
Other comprehensive income (loss)	$ (1,229)		(1,229)
Net income attributable to Avista Corporation shareholders	57,649			57,649
Cash dividends paid (common stock)				(21,545)
Ending Balance at Mar. 31, 2016	$ 1,589,591	$ 1,030,426	(7,879)	567,044
Beginning Balance Noncontrolling Interest at Dec. 31, 2015					$ (339)
Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Net income attributable to noncontrolling interests					16
Ending Balance Noncontrolling Interest at Mar. 31, 2016					(323)
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	1,589,268
Total equity	$ 1,648,476
Shares issued		198,218
Ending Balance (in shares) at Mar. 31, 2017	64,386,152	64,386,152
Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Equity compensation expense		$ 922
Issuance of common stock, net of issuance costs		315
Payment of minimum tax withholdings for share-based payment awards		(3,420)
Other comprehensive income (loss)	$ 183		183
Net income attributable to Avista Corporation shareholders	62,116			62,116
Cash dividends paid (common stock)				(23,167)
Ending Balance at Mar. 31, 2017	1,685,676	$ 1,073,098	$ (7,385)	$ 619,963
Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Net income attributable to noncontrolling interests					21
Ending Balance Noncontrolling Interest at Mar. 31, 2017	230				$ (230)
Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Total equity	$ 1,685,446