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Debt | 3 Months Ended
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Mar. 31, 2021
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 that can be drawn down in increments at any time. The Credit Line was amended in July 2017 and bears interest at 30-day LIBOR plus 1.10%. 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. 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. For the three months ended March 31, 2021 and 2020, the Company recorded interest expense on the Credit Line of $0.2 million and $0.3 million, respectively. Interest payments on the Credit Line were made within the same periods. As of March 31, 2021, remaining accrued interest was $1.1 million, and the total principal amount outstanding with accrued interest was $49.0 million. ​ ​ ​ ​ ​ ​ 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 are senior, unsecured obligations of the Company and bear 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 are 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 Company received net proceeds from the Convertible Notes of $278.3 million, after deducting the initial purchasers’ discounts and debt issuance costs. The Company used approximately $79.2 million of the net proceeds from the Convertible Notes offering to repay its obligations under the 2017 Term Loan with OrbiMed. ​ The holders of the Convertible Notes may convert all or a portion of their Convertible Notes at their option at any time prior to the close of business on the business day immediately preceding February 1, 2027 in multiples of $1,000 principal amount, under any the following circumstances: ​
| ● | During any fiscal quarter commencing after March 31, 2020 (and only during such fiscal quarter), if the last reported sale price of the Company’s common stock for at least 20 trading days (whether or not consecutive) during the period of 30 consecutive trading days ending on, and including, the last trading day of the immediately preceding fiscal quarter is greater than or equal to 130% of the conversion price on each applicable trading day.
| ● | During the five business day period after any five consecutive trading day period in which the trading price per $1,000 principal amount of Convertible Notes for each trading day of that five-day consecutive trading period was less than 98% of the product of the last reported sale price of the Company’s common stock and the conversion rate on each such trading day.
| ● | If the Company calls any or all of the Convertible Notes for redemption at any time prior to the close of business on the second business day prior to the redemption date.
| ● | Upon the occurrence of certain distributions.
| ● | Upon the occurrence of specified corporate transactions.
​ The Convertible Notes are 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 are subject to adjustment upon the occurrence of certain events but will not be adjusted for any accrued or unpaid interest. The holders of the Convertible Notes who redeem their Convertible Notes in connection with a make-whole fundamental change are, under certain circumstances, entitled to an increase in the conversion rate. Additionally, in the event of a fundamental change, the holders of the Convertible Notes may require the Company to repurchase for cash all or a portion of their Convertible Notes at a price equal to 100% of the principal amount, plus any accrued and unpaid interest. ​ The Company may not redeem the Convertible Notes prior to May 2024, and no sinking fund is provided for the Convertible Notes. The Company may redeem for cash all or any portion of the Convertible Notes, at the Company’s option, on or after May 2024, if the last reported sale price of the Company’s common stock has been at least 130% of the conversion price then in effect for at least 20 trading days during any 30 consecutive trading day period ending on the trading day immediately preceding the date on which the Company provides notice of redemption. The redemption price will be equal to 100% of the principal amount of the Convertible Notes to be redeemed plus accrued and unpaid interest. ​ Upon adoption of ASU 2020-06, the Company allocated all of the debt discount to long-term debt. The debt discount is amortized to interest expense using the effective interest method, computed to be 2.72%, over the life of the Convertible Notes or approximately its seven-year term. The outstanding Convertible Notes balances as of March 31, 2021 are summarized in the following table: ​
​ | ​ | ​ | ​
​ | March 31, | ​
​ | 2021 | ​
​ | (in thousands)
Long-Term Debt | ​ | ​ | ​
Outstanding Principal | $ | 287,500 | ​
Unamortized debt discount and issuance cost | ​ | (8,029) | ​
Net carrying amount | $ | 279,471 | ​
​ | ​ | ​ | ​
​ The following table presents total interest expense recognized related to the Convertible Notes during the three ended March 31, 2021: ​
​ | ​ | ​ | ​
​ | Three months ended
​ | March 31,
​ | 2021
​ | (in thousands)
Cash interest expense | ​ | ​ | ​
Contractual interest expense | $ | 1,617 | ​
Non-cash interest expense | ​ | ​ | ​
Amortization of debt discount and debt issuance cost | ​ | 304 | ​
Total interest expense | $ | 1,921 | ​
​

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