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Debt
 6 Months Ended
Jun. 30, 2024
Debt Disclosure [Abstract]  
Debt DEBT
Short-Term Debt
At June 30, 2024, June 30, 2023 and December 31, 2023, short-term debt consisted of the following:

June 30, 2024June 30, 2023December 31, 2023
In millionsBalance Outstanding
Weighted Average Interest Rate(1)
Balance Outstanding
Weighted Average Interest Rate(1)
Balance Outstanding
Weighted Average Interest Rate(1)
NW Natural:
Commercial paper$— — %$— — %$16.8 5.5 %
Other (NW Holdings):
Credit agreement79.0 6.4 %41.0 6.2 %73.0 6.4 %
NW Holdings$79.0 $41.0 $89.8 
(1) Weighted average interest rate on outstanding short-term debt

Long-Term Debt
At June 30, 2024, June 30, 2023 and December 31, 2023, NW Holdings' long-term debt consisted of the following:

June 30, 2024June 30, 2023December 31, 2023
In millionsBalance Outstanding
Weighted Average Interest Rate(1)
Balance Outstanding
Weighted Average Interest Rate(1)
Balance Outstanding
Weighted Average Interest Rate(2)
NW Natural first mortgage bonds$1,374.7 4.6 %$1,334.7 4.7 %$1,374.7 4.7 %
NW Holdings unsecured senior bonds150.0 5.8 %— — %— — %
NW Holdings credit agreement— — %100.0 5.5 %100.0 5.5 %
NWN Water credit agreement— — %50.0 5.5 %50.0 5.8 %
NWN Water term loan55.0 4.7 %55.0 4.8 %55.0 4.7 %
Other long-term debt6.3 5.9 6.6 
Long-term debt, gross1,586.0 1,545.6 1,586.3 
Less: unamortized debt issuance costs10.4 10.3 10.0 
Less: current maturities0.9 240.7 150.9 
Total long-term debt$1,574.7 $1,294.6 $1,425.4 
(1) Weighted average interest rate for the six months ended June 30, 2024 and June 30, 2023
(2) Weighted average interest rate for the year ended December 31, 2023

NW Natural's first mortgage bonds (FMBs) have maturity dates ranging from 2025 through 2053 and interest rates ranging from 2.82% to 7.85%. NW Holdings' unsecured senior bonds have maturity dates ranging from 2028 through 2029 and interest rates ranging from 5.78% to 5.84%. NWN Water's term loan is due in 2026. In March 2024, NW Holdings retired a $100.0 million credit agreement and NWN Water retired a $50.0 million credit agreement. No debt is scheduled to mature in the next twelve months as of June 30, 2024 at NW Natural and $0.9 million of debt is scheduled to mature in the next twelve months at NW Holdings.

Issuance of Long-Term Debt
In December 2023, NW Holdings entered into a Note Purchase Agreement between NW Holdings and the institutional investors named as purchasers therein. The Note Purchase Agreement provided for the issuance of (i) $100.0 million aggregate principal amount of NW Holdings’ 5.78% Senior Notes, Series A, due March 7, 2028 (5.78% Notes) and (ii) $50.0 million aggregate principal amount of NW Holdings’ 5.84% Senior Notes, Series B, due March 7, 2029 (5.84% Notes) in reliance on an exemption from registration under Section 4(a)(2) of the Securities Act of 1933, as amended. The 5.78% Notes and the 5.84% Notes were issued on March 7, 2024, pursuant to the Note Purchase Agreement. The proceeds from the Note Purchase Agreement were used to settle an existing term loan at NW Holdings for $100.0 million and make an equity contribution to NWN Water, which was used to settle an existing term loan for $50 million.

Interest Rate Swap Agreement
In January 2023, NWN Water entered into an interest rate swap agreement with major a financial institution for $55.0 million that effectively converted variable-rate debt to a fixed rate of 3.8%. Interest payments made between the effective date and expiration date are hedged by the swap agreement. The interest rate swap agreement expires in June 2026.
Fair Value of Long-Term Debt
NW Holdings' and NW Natural's outstanding debt does not trade in active markets. The fair value of debt is estimated using the value of outstanding debt at natural gas distribution companies with similar credit ratings, terms, and remaining maturities to NW Holdings' and NW Natural's debt that actively trade in public markets. These valuations are based on Level 2 inputs as defined in the fair value hierarchy. See Note 2 in the 2023 Form 10-K for a description of the fair value hierarchy.

The following table provides an estimate of the fair value of long-term debt, including current maturities of long-term debt, using market prices in effect on the valuation date:
June 30,December 31,
In thousands202420232023
NW Natural:
Gross long-term debt$1,374,700 $1,334,700 $1,374,700 
Unamortized debt issuance costs(9,634)(10,141)(9,968)
Carrying amount1,365,066 1,324,559 1,364,732 
Estimated fair value(1)
1,182,455 1,176,519 1,236,559 
NW Holdings:
Gross long-term debt$1,585,986 $1,545,553 $1,586,344 
Unamortized debt issuance costs(10,369)(10,261)(10,044)
Carrying amount1,575,617 1,535,292 1,576,300 
Estimated fair value(1)
1,393,946 1,385,612 1,447,941 
(1) Estimated fair value does not include unamortized debt issuance costs.