Cash Equivalents and Marketable Securities - Schedule of Estimated Fair Value of Cash Equivalents and Marketable Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Schedule Of Available For Sale Securities [Line Items]
Cash equivalents, amortized cost	$ 20,188	$ 19,407
Cash equivalents, gross unrealized losses	(1)	(1)
Cash equivalents, estimated fair value	20,187	19,406
Marketable securities, amortized cost	80,043	52,078
Marketable securities, gross unrealized gains	82
Marketable securities, gross unrealized losses	(14)	(26)
Marketable securities, estimated fair value	80,111	52,052
Money market funds
Schedule Of Available For Sale Securities [Line Items]
Cash equivalents, amortized cost	5,947	7,180
Cash equivalents, estimated fair value	5,947	7,180
Reverse repurchase agreements
Schedule Of Available For Sale Securities [Line Items]
Cash equivalents, amortized cost	6,250	6,250
Cash equivalents, estimated fair value	6,250	6,250
Commercial paper
Schedule Of Available For Sale Securities [Line Items]
Cash equivalents, amortized cost	7,991	5,977
Cash equivalents, gross unrealized losses	(1)	(1)
Cash equivalents, estimated fair value	7,990	5,976
Marketable securities, amortized cost	41,407	47,964
Marketable securities, gross unrealized gains	39
Marketable securities, gross unrealized losses	(1)	(24)
Marketable securities, estimated fair value	41,445	47,940
U.S. government securities
Schedule Of Available For Sale Securities [Line Items]
Marketable securities, amortized cost	38,636	4,114
Marketable securities, gross unrealized gains	43
Marketable securities, gross unrealized losses	(13)	(2)
Marketable securities, estimated fair value	$ 38,666	$ 4,112

Cash equivalents unrealized losses.

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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).

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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 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. Excludes cash and cash equivalents within disposal group and discontinued operation.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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