Cash, Cash Equivalents and Marketable Securities - Amortized Cost and Fair Value of Cash, Cash Equivalents and Marketable Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Cash and Cash Equivalents [Line Items]
Cash	$ 43,058	$ 5,222
Cash and cash equivalents	62,070	68,454
Gross Unrealized Gains	381	89
Gross Unrealized Losses	(2)	(86)
Total cash, cash equivalents and marketable securities	250,776	514,184
Total cash, cash equivalents and marketable securities at fair value	251,155	514,187
Money market funds
Cash and Cash Equivalents [Line Items]
Money market funds	11,527	63,232
Marketable securities
Cash and Cash Equivalents [Line Items]
Amortized Cost	188,706	445,730
Gross Unrealized Gains	381	89
Gross Unrealized Losses	(2)	(86)
Marketable securities	189,085	445,733
Commercial paper
Cash and Cash Equivalents [Line Items]
Money market funds	7,485
Amortized Cost	73,366	152,940
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Marketable securities	73,366	152,940
Corporate debt securities
Cash and Cash Equivalents [Line Items]
Amortized Cost	74,038	60,622
Gross Unrealized Gains	381	58
Gross Unrealized Losses	(2)	(75)
Marketable securities	74,417	60,605
Certificates of deposits
Cash and Cash Equivalents [Line Items]
Amortized Cost	41,302	128,647
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Marketable securities	$ 41,302	128,647
U.S Treasury securities
Cash and Cash Equivalents [Line Items]
Amortized Cost		103,521
Gross Unrealized Gains		31
Gross Unrealized Losses		(11)
Marketable securities		$ 103,541

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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