| Schedule of Fair Value Measurements of Financial Instruments |
The following tables present the level within the fair value hierarchy at which our financial instruments were measured: | | | | | | | | | | | | | | | | | | Fair Value Measurements Using | | | | Quoted Prices in
Active Markets for
Identical Assets
(Level 1) | | Significant Other
Observable Inputs
(Level 2) | | Significant
Unobservable
Inputs
(Level 3) | | Fair Value | As of December 31, 2019 | (In Thousands) | U.S. Treasury securities and obligations of U.S. government agencies | $ | 48,929 |
| | $ | — |
| | $ | — |
| | $ | 48,929 |
| Municipal debt securities | — |
| | 190,216 |
| | — |
| | 190,216 |
| Corporate debt securities | — |
| | 684,881 |
| | — |
| | 684,881 |
| Asset-backed securities | — |
| | 172,642 |
| | — |
| | 172,642 |
| Cash, cash equivalents and short-term investments | 85,361 |
| | — |
| | — |
| | 85,361 |
| Total assets | $ | 134,290 |
| | $ | 1,047,739 |
| | $ | — |
| | $ | 1,182,029 |
| Warrant liability | — |
| | — |
| | 7,641 |
| | 7,641 |
| Total liabilities | $ | — |
| | $ | — |
| | $ | 7,641 |
| | $ | 7,641 |
|
| | | | | | | | | | | | | | | | | | Fair Value Measurements Using | | | | Quoted Prices in
Active Markets for
Identical Assets
(Level 1) | | Significant Other
Observable Inputs
(Level 2) | | Significant
Unobservable
Inputs
(Level 3) | | Fair Value | As of December 31, 2018 | (In Thousands) | U.S. Treasury securities and obligations of U.S. government agencies | $ | 46,830 |
| | $ | — |
| | $ | — |
| | $ | 46,830 |
| Municipal debt securities | — |
| | 91,257 |
| | — |
| | 91,257 |
| Corporate debt securities | — |
| | 543,238 |
| | — |
| | 543,238 |
| Asset-backed securities | — |
| | 171,325 |
| | — |
| | 171,325 |
| Cash, cash equivalents and short-term investments | 84,134 |
| | — |
| | — |
| | 84,134 |
| Total assets | $ | 130,964 |
| | $ | 805,820 |
| | $ | — |
| | $ | 936,784 |
| Warrant liability | — |
| | — |
| | 7,296 |
| | 7,296 |
| Total liabilities | $ | — |
| | $ | — |
| | $ | 7,296 |
| | $ | 7,296 |
|
|
| Roll-Forward of Level 3 Liabilities Measured at Fair Value |
The following is a roll-forward of Level 3 liabilities measured at fair value: | | | | | | | | | | | | | | For the year ended December 31, | | 2019 | | 2018 | | 2017 | | (In Thousands) | Balance, January 1 | $ | 7,296 |
| | $ | 7,472 |
| | $ | 3,367 |
| Change in fair value of warrant liability included in earnings | 8,657 |
| | 1,397 |
| | 4,105 |
| Issuance of common stock on warrant exercise | (8,312 | ) | | (1,573 | ) | | — |
| Balance, December 31 | $ | 7,641 |
| | $ | 7,296 |
| | $ | 7,472 |
|
|