Fair Value Measurements - Summary of the Company's Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Fair value
Debt securities	$ 396,310
Contingent consideration	37,600	$ 65,200
Recurring Basis
Fair value
Cash equivalents	62,556	54,590
Contingent consideration	37,600	65,200
Common stock warrants	772	1,205
Assets, Total	497,238	470,649
Recurring Basis \| Level 1
Fair value
Cash equivalents	62,556	54,590
Assets, Total	131,260	114,697
Recurring Basis \| Level 2
Fair value
Assets, Total	327,606	289,055
Recurring Basis \| Level 3
Fair value
Contingent consideration	37,600	65,200
Common stock warrants	772	1,205
Assets, Total	38,372	66,897
U.S. government and agency debt securities \| Recurring Basis
Fair value
Debt securities	119,296	98,513
U.S. government and agency debt securities \| Recurring Basis \| Level 1
Fair value
Debt securities	68,704	60,107
U.S. government and agency debt securities \| Recurring Basis \| Level 2
Fair value
Debt securities	50,592	38,406
Corporate debt securities \| Recurring Basis
Fair value
Debt securities	185,073	173,637
Corporate debt securities \| Recurring Basis \| Level 2
Fair value
Debt securities	185,073	173,145
Corporate debt securities \| Recurring Basis \| Level 3
Fair value
Debt securities		492
International government agency debt securities \| Recurring Basis
Fair value
Debt securities	91,941	77,504
International government agency debt securities \| Recurring Basis \| Level 2
Fair value
Debt securities	$ 91,941	$ 77,504

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

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-Publisher FASB
-Name Accounting Standards Codification
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Amount of asset recognized arising from contingent consideration in a business combination, expected to be realized beyond one year or the normal operating cycle, if longer.

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Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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Value of outstanding derivative securities that permit the holder the right to purchase securities (usually equity) from the issuer at a specified price.

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