Long-Term Debt (Tables)

12 Months Ended

Dec. 31, 2019

Long-term Debt, Unclassified [Abstract]

Schedule of Maturities of Long-term Debt [Table Text Block]

	2020		2021		2022		2023		2024		Thereafter		Total
Debt maturities	$	52,000	$	—	$	250,000	$	13,500	$	15,000	$	1,631,547	$	1,962,047

Schedule of Long-term Debt Instruments [Table Text Block]

Maturity Year	Description	Interest Rate	2019			2018
Avista Corp. Secured Long-Term Debt
2019	First Mortgage Bonds	5.45%	—			90,000
2020	First Mortgage Bonds	3.89%	52,000			52,000
2022	First Mortgage Bonds	5.13%	250,000			250,000
2023	Secured Medium-Term Notes	7.18%-7.54%	13,500			13,500
2028	Secured Medium-Term Notes	6.37%	25,000			25,000
2032	Secured Pollution Control Bonds (1)	(1)	66,700			66,700
2034	Secured Pollution Control Bonds (1)	(1)	17,000			17,000
2035	First Mortgage Bonds	6.25%	150,000			150,000
2037	First Mortgage Bonds	5.70%	150,000			150,000
2040	First Mortgage Bonds	5.55%	35,000			35,000
2041	First Mortgage Bonds	4.45%	85,000			85,000
2044	First Mortgage Bonds	4.11%	60,000			60,000
2045	First Mortgage Bonds	4.37%	100,000			100,000
2047	First Mortgage Bonds	4.23%	80,000			80,000
2047	First Mortgage Bonds	3.91%	90,000			90,000
2048	First Mortgage Bonds	4.35%	375,000			375,000
2049	First Mortgage Bonds (2)	3.43%	180,000			—
2051	First Mortgage Bonds	3.54%	175,000			175,000
	Total Avista Corp. secured long-term debt		1,904,200			1,814,200
Alaska Electric Light and Power Company Secured Long-Term Debt
2044	First Mortgage Bonds	4.54%	75,000			75,000
	Total secured long-term debt		1,979,200			1,889,200
Alaska Energy and Resources Company Unsecured Long-Term Debt
2019	Unsecured Term Loan	3.85%	—			15,000
2024	Unsecured Term Loan	3.44%	15,000			—
	Total secured and unsecured long-term debt		1,994,200			1,904,200
Other Long-Term Debt Components
	Capital lease obligations (3)		—			57,210
	Unamortized debt discount		(788		)	(882		)
	Unamortized long-term debt issuance costs		(13,944		)	(13,654		)
	Total		1,979,468			1,946,874
	Secured Pollution Control Bonds held by Avista Corporation (1)		(83,700		)	(83,700		)
	Current portion of long-term debt and capital leases		(52,000		)	(107,645		)
	Total long-term debt and capital leases		$	1,843,768		$	1,755,529

(1) In December 2010, $66.7 million and $17.0 million of the City of Forsyth, Montana Pollution Control Revenue Refunding Bonds (Avista Corporation Colstrip Project) due in 2032 and 2034, respectively, which had been held by Avista Corp. since 2008 and 2009, respectively, were refunded by new variable rate bond issues (Series 2010A and Series 2010B). The new bonds were not offered to the public and were purchased by Avista Corp. due to market conditions. The Company expects that at a later date, subject to market conditions, these bonds may be remarketed to unaffiliated investors. So long as Avista Corp. is the holder of these bonds, the bonds will not be reflected as an asset or a liability on Avista Corp.'s Consolidated Balance Sheets.

(2) In November 2019, the Company issued and sold $180.0 million of 3.43 percent first mortgage bonds due in 2049 pursuant to a bond purchase agreement with institutional investors in the private placement market. The total net proceeds from the sale of the bonds were used to repay maturing long-term debt of $90.0 million, repay a portion of the outstanding balance under Avista Corp.'s $400.0 million committed line of credit and for other general corporate purposes. In connection with the issuance and sale of the first mortgage bonds, the Company cash settled six interest rate swap derivatives (notional aggregate amount of $70.0 million) and paid a net amount of $13.3 million. See note 7 for a discussion of interest rate swap derivatives.

(3) Effective January 1, 2019, due to the adoption of the new lease standard (ASU 2016-02), capital leases will now be defined as finance leases and are presented in "Other current liabilities" and "Other non-current liabilities and deferred credits" on the Consolidated Balance Sheet such that their presentation as of December 31, 2019 is consistent with operating leases. See Notes 2 and 5 for further discussion of the new lease standard.