Long-Term Debt (Tables)
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12 Months Ended |
Dec. 31, 2017 |
|---|
| Long-term Debt, Unclassified [Abstract] |
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| Schedule of long-term debt |
As of December 31, 2017 and 2016, the carrying amount of the Notes on the consolidated balance sheets is calculated as follows: | | | | | | | | | | December 31, 2017 | | December 31, 2016 | Convertible senior notes, principal amount | $ | 230,000,000 |
| | $ | 230,000,000 |
| Unamortized debt discount | (15,930,370 | ) | | (22,070,838 | ) | Unamortized debt issuance costs | (3,150,695 | ) | | (4,365,151 | ) | Convertible senior notes, net | $ | 210,918,935 |
| | $ | 203,564,011 |
|
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| Schedule of interest expense related to Notes |
For 2017, 2016 and 2015, interest expense related to the Notes consisted of the following: | | | | | | | | | | | | | | December 31, 2017 | | December 31, 2016 | | December 31, 2015 | Contractual coupon interest | $ | 5,750,000 |
| | $ | 5,750,000 |
| | $ | 3,769,444 |
| Debt discount amortization | 6,140,468 |
| | 5,764,549 |
| | 3,645,613 |
| Debt issuance cost amortization | 1,214,456 |
| | 1,140,108 |
| | 721,026 |
| Interest expense, Notes | $ | 13,104,924 |
| | $ | 12,654,657 |
| | $ | 8,136,083 |
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| Schedule of maturities of long-term debt |
The undiscounted interest and principal payments due in relation to the Notes from December 31, 2017 to the maturity of the Notes on May 1, 2020 are as follows: | | | | | | | | | | | | | Total | 2018 | 2019 | 2020 | Senior convertible notes, including interest | $ | 244,375,000 |
| 5,750,000 |
| 5,750,000 |
| $ | 232,875,000 |
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