| Fair Value of Financial Instruments |
Fair Value of Financial Instruments The following is a list of those assets and liabilities that are measured at fair value by hierarchy level: | | | | | | | | | | | | | | | | | | 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 September 30, 2016 | (In Thousands) | U.S. Treasury securities and obligations of U.S. government agencies | $ | 45,398 |
| | $ | 12,479 |
| | $ | — |
| | $ | 57,877 |
| Municipal debt securities | — |
| | 40,933 |
| | — |
| | 40,933 |
| Corporate debt securities | — |
| | 346,329 |
| | — |
| | 346,329 |
| Asset-backed securities | — |
| | 122,069 |
| | — |
| | 122,069 |
| Cash, cash equivalents and short-term investments | 118,886 |
| | — |
| | — |
| | 118,886 |
| Total assets | $ | 164,284 |
| | $ | 521,810 |
| | $ | — |
| | $ | 686,094 |
| Warrant liability | — |
| | — |
| | 1,654 |
| | 1,654 |
| Total liabilities | $ | — |
| | $ | — |
| | $ | 1,654 |
| | $ | 1,654 |
|
| | | | | | | | | | | | | | | | | | 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, 2015 | (In Thousands) | U.S. Treasury securities and obligations of U.S. government agencies | $ | 65,185 |
| | $ | 19,297 |
| | $ | — |
| | $ | 84,482 |
| Municipal debt securities | — |
| | 20,079 |
| | — |
| | 20,079 |
| Corporate debt securities | — |
| | 333,327 |
| | — |
| | 333,327 |
| Asset-backed securities | — |
| | 100,793 |
| | — |
| | 100,793 |
| Cash, cash equivalents and short-term investments | 77,872 |
| | — |
| | — |
| | 77,872 |
| Total assets | $ | 143,057 |
| | $ | 473,496 |
| | $ | — |
| | $ | 616,553 |
| Warrant liability | — |
| | — |
| | 1,467 |
| | 1,467 |
| Total liabilities | $ | — |
| | $ | — |
| | $ | 1,467 |
| | $ | 1,467 |
|
The following is a roll-forward of Level 3 liabilities measured at fair value: | | | | | | | | | | For the nine months ended September 30, | Warrant Liability | 2016 | | 2015 | | (In Thousands) | Balance, January 1 | $ | 1,467 |
| | $ | 3,372 |
| Change in fair value of warrant liability included in earnings | 187 |
| | (1,473 | ) | Balance, September 30 | $ | 1,654 |
| | $ | 1,899 |
|
We revalue the warrant liability quarterly using a Black-Scholes option-pricing model, in combination with a binomial model, and we value the pricing protection features within the warrants using a Monte-Carlo simulation model. As of September 30, 2016, the assumptions used in the option-pricing model were as follows: a common stock price as of September 30, 2016 of $7.62, risk free interest rate of 1.15%, expected life of 5.08 years, expected volatility of 33.1% and a dividend yield of 0%. The change in fair value is primarily attributable to an increase in the price of our common stock from December 31, 2015 to September 30, 2016. |