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Debt | 6 Months Ended
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Jun. 30, 2025
Debt |
Debt | 10. Debt Credit Line Agreement In September 2015, the Company entered into a credit line with UBS (the “Credit Line”) providing for a $50.0 million revolving line of credit. The Credit Line was subsequently increased from $50.0 million to $150.0 million in 2020. In June 2023, the Credit Line decreased from $150.0 million to $100.0 million. The Credit Line is secured by a first priority lien and security interest in the Company’s money market and marketable securities held in its managed investment account with UBS. The Company is required to maintain a minimum of at least $150.0 million in its UBS accounts as collateral, which is classified as cash, cash equivalents, and short-term investments in the consolidated balance sheets. UBS has the right to demand full or partial payment of the Credit Line obligations and terminate the Credit Line, in its discretion and without cause, at any time. In October 2023, the interest rate for the Credit Line was changed to the 30-day SOFR average, plus 0.5%. As of June 30, 2025, the Company has drawn down a total of $80.0 million, and there is $20.0 million remaining and available on the Credit Line. The interest rate as of June 30, 2025 was 4.82%. For the three months ended June 30, 2025 and 2024, the Company recorded interest expense on the Credit Line of $1.0 million and $1.2 million, respectively. For the six months ended June 30, 2025 and 2024, the Company recorded interest expense on the Credit Line of $2.0 million and $2.4 million, respectively. Interest payments on the Credit Line were made within the same periods. As of June 30, 2025 and December 31, 2024, the total principal amount outstanding with accrued interest was $80.3 million and $80.4 million, respectively. Convertible Notes ​ In April 2020, the Company issued $287.5 million aggregate principal amount of Convertible Notes due 2027 in a private placement offering to qualified institutional buyers pursuant to Rule 144A under the Securities Act of 1933, as amended. The Convertible Notes were senior, unsecured obligations of the Company and bore interest at a rate of 2.25% per year, payable in cash semi-annually. The Convertible Notes mature in May 2027, unless earlier converted, repurchased or redeemed in accordance with their terms. Upon conversion, the Convertible Notes were convertible into cash, shares of the Company’s common stock or a combination of cash and shares of the Company’s common stock, at the Company’s election. The Convertible Notes were convertible into shares of the Company’s common stock, par value $0.0001 per share, at an initial conversion rate of 25.7785 shares of common stock per $1,000 principal amount of the Convertible Notes, which is equivalent to an initial conversion price of approximately $38.79 per share of common stock, convertible to 7,411,704 shares of common stock. The conversion rate and corresponding conversion price were subject to adjustment upon the occurrence of certain events. On July 19, 2024, the Company elected to exercise its optional redemption right to redeem all $287.5 million aggregate principal amount of its outstanding 2.25% Convertible Notes due 2027 and instructed Wilmington Trust, National Association, as trustee under the Convertible Notes Indenture (the “Indenture Agreement”) governing the Convertible Notes, to issue a redemption notice to registered holders of the Convertible Notes. The date fixed for the redemption of the Convertible Notes was October 11, 2024 (the “Redemption Date”). The redemption price for the Convertible Notes was equal to 100% of the principal amount of the Convertible Notes to be redeemed plus accrued and unpaid interest to, but excluding, the Redemption Date. The Company elected physical settlement with the Company’s shares of common stock as the settlement method to apply to all conversions of the Convertible Notes. All terms and conditions associated with physical settlement are noted within the terms of the original Indenture Agreement. The conversion rate for holders who converted their Convertible Notes in connection with the Company’s election to redeem the Convertible Notes was increased by 0.4284 additional shares pursuant to the Indenture Agreement. The following tables present total interest expense recognized related to the Convertible Notes during the three and six months ended June 30, 2025 and 2024: ​
​ | ​ | ​ | ​ | ​ | ​ | ​
​ | Three months ended | ​
​ | June 30, | ​
​ | 2025 | ​ | 2024 | ​
​ | (in thousands) | ​
Cash interest expense | ​ | ​ | ​ | ​ | ​ | ​
Contractual interest expense | $ | — | ​ | $ | 1,617 | ​
Non-cash interest expense | ​ | ​ | ​ | ​ | ​ | ​
Amortization of debt discount and debt issuance cost | ​ | — | ​ | ​ | 330 | ​
Total interest expense | $ | — | ​ | $ | 1,947 | ​
​
​ | ​ | ​ | ​ | ​ | ​ | ​
​ | Six months ended June 30, | ​
​ | 2025 | ​ | 2024 | ​
​ | (in thousands) | ​
Cash interest expense | ​ | ​ | ​ | ​ | ​ | ​
Contractual interest expense | $ | — | ​ | $ | 3,234 | ​
Non-cash interest expense | ​ | ​ | ​ | ​ | ​ | ​
Amortization of debt discount and debt issuance cost | ​ | — | ​ | ​ | 658 | ​
Total interest expense | $ | — | ​ | $ | 3,892 | ​
​

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