Investments - Summary of Investments (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Total	$ 622,271	$ 703,267
Gross Unrealized Gains	5,692	2,031
Gross Unrealized Losses	(71)	(343)
Estimated Fair Value	627,892	704,955
Certificates of deposit
Debt Securities, Available-for-sale [Line Items]
Total	3,169	5,118
Gross Unrealized Gains	85	27
Gross Unrealized Losses	0	0
Estimated Fair Value	3,254	5,145
Commercial paper
Debt Securities, Available-for-sale [Line Items]
Total	19,987
Gross Unrealized Gains	0
Gross Unrealized Losses	(5)
Estimated Fair Value	19,982
Corporate notes and bonds
Debt Securities, Available-for-sale [Line Items]
Total	442,616	471,172
Gross Unrealized Gains	5,407	1,950
Gross Unrealized Losses	(46)	(214)
Estimated Fair Value	447,977	472,908
U.S. Treasuries
Debt Securities, Available-for-sale [Line Items]
Total	71,053	48,086
Gross Unrealized Gains	51	2
Gross Unrealized Losses	(12)	(19)
Estimated Fair Value	71,092	48,069
U.S. Government agencies
Debt Securities, Available-for-sale [Line Items]
Total	85,446	178,891
Gross Unrealized Gains	149	52
Gross Unrealized Losses	(8)	(110)
Estimated Fair Value	$ 85,587	$ 178,833

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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