Fair Value of Financial Assets and Liabilities (Details) $ in Thousands	6 Months Ended	12 Months Ended
Jun. 30, 2020 USD ($) security	Dec. 31, 2019 USD ($) security
Fair Value, Assets Transfers
Fair value of assets transferred from Level 1 to Level 2	$ 0	$ 0
Fair value of assets transferred from Level 2 to Level 1	0	0
Fair value of assets transferred from Level 1 to Level 3	0	0
Fair value of assets transferred from Level 2 to Level 3	0	0
Fair value of assets transferred from Level 3 to Level 1	0	0
Fair value of assets transferred from Level 3 to Level 2	$ 0	$ 0
Number of securities \| security	17	7
Unrealized loss position	$ 113,682	$ 43,107
U.S. Treasury Notes
Assets
Amortized cost of short-term investments	128,933	186,415
Unrealized gain on short-term investments	9	37
Short-term investments	128,942	186,452
Fair Value \| Recurring basis
Assets
Assets	206,521	222,061
Fair Value \| Recurring basis \| Money Market Funds
Assets
Restricted cash	210	210
Cash equivalents	44,473	25,207
Fair Value \| Recurring basis \| U.S. Treasury Notes
Assets
Cash equivalents	32,896	10,192
Short-term investments	128,942	186,452
Fair Value \| Recurring basis \| Level 1
Assets
Assets	44,683	25,417
Fair Value \| Recurring basis \| Level 1 \| Money Market Funds
Assets
Restricted cash	210	210
Cash equivalents	44,473	25,207
Fair Value \| Recurring basis \| Level 2
Assets
Assets	161,838	196,644
Fair Value \| Recurring basis \| Level 2 \| U.S. Treasury Notes
Assets
Cash equivalents	32,896	10,192
Short-term investments	$ 128,942	$ 186,452

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Amount of transfers of assets measured on a recurring basis out of Level 2 of the fair value hierarchy into Level 3.

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Amount of transfers of assets measured on a recurring basis out of Level 3 of the fair value hierarchy into Level 1.

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Amount of transfers of assets measured on a recurring basis out of Level 3 of the fair value hierarchy into Level 2.

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Represents the number of securities

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

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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), classified as current.

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

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Amount of cash restricted as to withdrawal or usage. Cash includes, but is not limited to, currency on hand, demand deposits with banks or financial institutions, and other accounts with general characteristics of demand deposits.

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