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Convertible debt (Tables) | 9 Months Ended
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Sep. 30, 2021
Debt Disclosure [Abstract] |
Schedule of Debt [Table Text Block] | The following is a summary of the Company's convertible senior notes as of September 30, 2021 (in thousands):
| Date of Issuance |  | Unpaid Principal Balance |  | Net Carrying Amount |  | Contractual Interest Rates
|  |  | Current |  | Noncurrent |
1% Convertible Notes due in 2024 ("2024 Notes") | May 2019 |  | $ | 143,750 |  |  | $ | — |  |  | $ | 141,433 |  |  | 1%
2.25% Convertible Notes due in 2027 ("2027 Notes") | September 2020 |  | $ | 150,000 |  |  | $ | — |  |  | $ | 146,481 |  |  | 2.25%
Convertible Debt [Table Text Block] | The Notes consist of the following (in thousands):
| September 30, 2021 |  | December 31, 2020
Liability component: |  |  |
Principal | $ | 293,750 |  |  | $ | 293,750 |
Less: debt discount and issuance cost, net of amortization | (5,836) |  |  | (75,722) |
Net carrying amount | $ | 287,914 |  |  | $ | 218,028 |
Equity component(1) | $ | — |  |  | $ | 80,098 |
(1) Recorded within additional paid-in capital in the unaudited condensed consolidated balance sheet. As of December 31, 2020, it included $47.2 million and $32.9 million related to the 2027 and 2024 Notes, respectively, which was net of $1.3 million and $1.1 million issuance cost in equity, respectively. The following table sets forth total interest expense recognized related to the Notes (in thousands):
| Three Months Ended September 30, |  | Nine Months Ended September 30,
| 2021 |  | 2020 |  | 2021 |  | 2020
Coupon interest | $ | 1,203 |  |  | $ | 500 |  |  | $ | 3,609 |  |  | $ | 1,219 |
Amortization of debt issuance costs | 373 |  |  | 174 |  |  | 1,119 |  |  | 488 |
Amortization of debt discount | — |  |  | 1,824 |  |  | — |  |  | 4,938 |
Total | $ | 1,576 |  |  | $ | 2,498 |  |  | $ | 4,728 |  |  | $ | 6,645 |

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- Definition Tabular disclosure of convertible debt instrument. Includes, but is not limited to, principal amount and amortized premium or discount. + References No definition available. + Details
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- Definition Tabular disclosure of information pertaining to short-term and long-debt instruments or arrangements, including but not limited to identification of terms, features, collateral requirements and other information necessary to a fair presentation. + References No definition available. + Details
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