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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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Amount of transfers of assets measured on a recurring basis out of Level 1 of the fair value hierarchy into Level 2.

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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 1.

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Fair Value Measurements - (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019
Fair value of the Company’s financial assets
Marketable securities	$ 268,672	$ 300,514
Assets transferred from level 1 to level 2	0		$ 0
Assets transferred from level 2 to level 1	0		$ 0
Carrying Amount
Fair value of the Company’s financial assets
Total financial assets	276,949	319,855
Fair Value \| Quoted Prices in Active Markets (Level 1)
Fair value of the Company’s financial assets
Total financial assets	8,277	19,341
Fair Value \| Significant Other Observable Inputs (Level 2)
Fair value of the Company’s financial assets
Total financial assets	268,672	300,514
Money market funds (cash equivalents) \| Carrying Amount
Fair value of the Company’s financial assets
Money market funds (cash equivalents)	8,277	19,341
Money market funds (cash equivalents) \| Fair Value \| Quoted Prices in Active Markets (Level 1)
Fair value of the Company’s financial assets
Money market funds (cash equivalents)	8,277	19,341
U.S. treasury securities \| Carrying Amount
Fair value of the Company’s financial assets
Marketable securities		4,991
U.S. treasury securities \| Fair Value \| Significant Other Observable Inputs (Level 2)
Fair value of the Company’s financial assets
Marketable securities		4,991
Agency bonds \| Carrying Amount
Fair value of the Company’s financial assets
Marketable securities	7,365	24,451
Agency bonds \| Fair Value \| Significant Other Observable Inputs (Level 2)
Fair value of the Company’s financial assets
Marketable securities	7,365	24,451
Corporate bonds \| Carrying Amount
Fair value of the Company’s financial assets
Marketable securities	254,327	271,072
Corporate bonds \| Fair Value \| Significant Other Observable Inputs (Level 2)
Fair value of the Company’s financial assets
Marketable securities	254,327	$ 271,072
Commercial Paper \| Carrying Amount
Fair value of the Company’s financial assets
Marketable securities	6,980
Commercial Paper \| Fair Value \| Significant Other Observable Inputs (Level 2)
Fair value of the Company’s financial assets
Marketable securities	$ 6,980