Fair Value of Financial Assets and Liabilities - Marketable Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Fair Value of Financial Assets and Liabilities
Amortized Cost	$ 168,904	$ 230,155
Gross Unrealized Gains	642	54
Gross Unrealized Losses	(11)	(44)
Fair Value	169,535	230,165
Corporate Debt Securities and Commercial Paper
Fair Value of Financial Assets and Liabilities
Amortized Cost	168,904	230,155
Gross Unrealized Gains	642	54
Gross Unrealized Losses	(11)	(44)
Fair Value	169,535	230,165
Estimated fair value \| Recurring \| Corporate Debt Securities and Commercial Paper
Fair Value of Financial Assets and Liabilities
Fair Value	169,535	230,165
Level 2 \| Estimated fair value \| Recurring \| Corporate Debt Securities and Commercial Paper
Fair Value of Financial Assets and Liabilities
Fair Value	$ 169,535	$ 230,165

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) 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, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) 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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Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
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-Publisher FASB
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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

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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-URI http://asc.fasb.org/extlink&oid=118942338&loc=SL82898722-210454

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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