The following table presents details of our convertible senior notes, which are further discussed below (original principal in thousands): | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Month Issued | | Maturity Date | | Free Convertibility Date | | Redemption Date | | Original Principal (including overallotment) | | Initial Conversion Rate per $1,000 Principal | | Initial Conversion Price | 2026 Notes | | August 2019 | | August 15, 2026 | | May 15, 2026 | | August 21, 2023 | | $ | 345,000 | | | 12.4756 | | $ | 80.16 | | 2028 Notes | | August 2023 | | August 15, 2028 | | May 15, 2028 | | August 21, 2026 | | $ | 702,000 | | | 7.4690 | | $ | 133.89 | |
The net carrying amount of the Notes was as follows (in thousands): | | | | | | | | | | | | | | | | | | | | | | | | | March 31, 2024 | | December 31, 2023 | | 2026 Notes | | 2028 Notes | | 2026 Notes | | 2028 Notes | | Principal | $ | 71,242 | | | $ | 702,000 | | | $ | 71,242 | | | $ | 702,000 | | | Unamortized issuance costs | (643) | | | (9,536) | | | (711) | | | (10,076) | | | Net carrying amount | $ | 70,599 | | | $ | 692,464 | | | $ | 70,531 | | | $ | 691,924 | | | | | | | | | | | | | | | | | |
Interest expense related to the Notes was as follows (in thousands): | | | | | | | | | | | | | | | | | Three months ended March 31, | | | | 2024 | | 2023 | | | | | | Contractual interest expense | $ | 2,394 | | | $ | 970 | | | | | | | Amortization of issuance costs | 608 | | | 325 | | | | | | | Total interest expense | $ | 3,002 | | | $ | 1,295 | | | | | |
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