| Net Carrying Amount of Convertible Notes |
The net carrying amount of the Notes were as follows (in thousands):
| | | | | | | | | | | | | | | | | | Principal outstanding | | Unamortized debt discount | | Unamortized debt issuance costs | | Net carrying value | September 30, 2019 | | | | | | | | 2023 Notes | $ | 862,500 |
| | $ | (117,932 | ) | | $ | (3,647 | ) | | $ | 740,921 |
| 2022 Notes | 211,726 |
| | (21,400 | ) | | (2,378 | ) | | 187,948 |
| Total | $ | 1,074,226 |
| | $ | (139,332 | ) | | $ | (6,025 | ) | | $ | 928,869 |
| | | | | | | | | December 31, 2018 | | | | | | | | 2023 Notes | $ | 862,500 |
| | $ | (138,924 | ) | | $ | (5,054 | ) | | $ | 718,522 |
| 2022 Notes | 211,728 |
| | (27,569 | ) | | (2,986 | ) | | 181,173 |
| | $ | 1,074,228 |
| | $ | (166,493 | ) | | $ | (8,040 | ) | | $ | 899,695 |
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The net carrying amount of the equity component of the 2023 Notes and 2022 Notes were as follows (in thousands):
| | | | | | | | | | | | | | Amount allocated to conversion option | | Less: allocated issuance costs | | Equity component, net | September 30, 2019 and December 31, 2018 | | | | | | 2023 Notes | $ | 155,250 |
| | $ | (1,231 | ) | | $ | 154,019 |
| 2022 Notes | 41,481 |
| | (1,108 | ) | | 40,373 |
| Total | $ | 196,731 |
| | $ | (2,339 | ) | | $ | 194,392 |
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| Interest Expense on Convertible Notes |
The Company recognized interest expense on the Notes as follows (in thousands, except for percentages):
| | | | | | | | | | | | | | | | | | Three Months Ended September 30, | | Nine Months Ended September 30, | | 2019 | | 2018 | | 2019 | | 2018 | Contractual interest expense | $ | 1,277 |
| | $ | 1,469 |
| | $ | 3,831 |
| | $ | 2,732 |
| Amortization of debt discount and issuance costs | 9,843 |
| | 11,627 |
| | 29,176 |
| | 22,850 |
| Total | $ | 11,120 |
| | $ | 13,096 |
| | $ | 33,007 |
| | $ | 25,582 |
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