At September 30, 2024 and December 31, 2023, our long-term debt and interest rates on that debt were as follows (dollars in millions):


	September 30,		December 31,
	2024		2023
Revolving Credit Facility	$	—	$	—
3.65% Senior Notes, net of discount of $0.1 million as of December 31, 2023, due September 2024		—		399.9
3.40% Senior Notes, net of discount of $0.6 million and $0.7 million as of September 30, 2024 and December 31, 2023, respectively, due December 2027		499.4		499.3
3.00% Senior Notes, net of discount of $0.4 million as of both September 30, 2024 and December 31, 2023, due December 2029		499.6		499.6
5.70% Senior Notes, net of discount of $0.3 million as of both September 30, 2024 and December 31, 2023, due December 2033		399.7		399.7
4.05% Senior Notes, net of discount of $3.2 million and $3.3 million as of September 30, 2024 and December 31, 2023, respectively, due December 2049		396.8		396.7
3.05% Senior Notes, net of discount of $3.4 million and $3.5 million as of September 30, 2024 and December 31, 2023, respectively, due October 2051		696.6		696.5
Total		2,492.1		2,891.7
Less current portion (a)		—		399.6
Less unamortized debt issuance costs		18.4		19.9
Total long-term debt	$	2,473.7	$	2,472.2

(a)

As of September 30, 2024, there are no unamortized debt issuance costs associated with the current portion of long-term debt, as the 2024 senior notes due September 2024 were repaid on September 15, 2024. As of December 31, 2023, the current portion of long-term debt excludes unamortized debt issuance costs of $0.3 million.

On September 15, 2024, we used the net proceeds from the November 2023 offering of the 5.70% senior notes due 2033 and cash on hand to repay our outstanding 3.65% senior notes due 2024. The repayment of the old 3.65% notes was $407.3 million, which included principal and accrued interest.

For the nine months ended September 30, 2024 and 2023, cash payments for interest were $61.4 million and $49.9 million, respectively.

Included in interest expense, net is the amortization of financing costs, which includes the amortization of debt issuance costs and amortization of bond discount. For the three months ended September 30, 2024 and 2023, amortization of debt issuance costs was $0.5 million and $0.4 million,

respectively, and during the nine months ended September 30, 2024 and 2023, amortization of debt issuance costs was $1.4 million and $1.2 million, respectively. For both the three and nine month periods ended September 30, 2024 and 2023, the amortization of bond discount was insignificant.

At September 30, 2024, we had $2,492.1 million of fixed-rate senior notes outstanding. The fair value of our fixed-rate debt was estimated to be $2,208.8 million. The difference between the book value and fair value is due to the difference between the period-end market interest rate and the stated rate of our fixed-rate debt. We estimated the fair value of our fixed-rate debt using quoted market prices (Level 2 inputs) within the fair value hierarchy, which is further defined in Note 2, Summary of Significant Accounting Policies, of the Notes to Consolidated Financial Statements in "Part II, Item 8. Financial Statements and Supplementary Data" of our 2023 Annual Report on Form 10-K.

For more information on our long-term debt and interest rates on that debt, see Note 10, Debt, of the Notes to Consolidated Financial Statements in "Part II, Item 8. Financial Statements and Supplementary Data" of our 2023 Annual Report on Form 10-K.