Cash Equivalents and Marketable Securities - Schedule of Estimated Fair Value of Cash Equivalents and Marketable Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Schedule Of Available For Sale Securities [Line Items]
Cash equivalents, amortized cost	$ 19,047	$ 8,924
Cash equivalents, estimated fair value	19,048	8,924
Marketable securities, amortized cost	51,670	37,584
Marketable securities, gross unrealized gains	8
Marketable securities, gross unrealized losses	(64)	(102)
Marketable securities, estimated fair value	51,614	37,482
Money market funds
Schedule Of Available For Sale Securities [Line Items]
Cash equivalents, amortized cost	6,807	1,674
Cash equivalents, estimated fair value	6,807	1,674
Reverse repurchase agreements
Schedule Of Available For Sale Securities [Line Items]
Cash equivalents, amortized cost	6,250	7,250
Cash equivalents, estimated fair value	6,250	7,250
Commercial paper
Schedule Of Available For Sale Securities [Line Items]
Cash equivalents, amortized cost	5,990
Cash equivalents, estimated fair value	5,991
Commercial paper
Schedule Of Available For Sale Securities [Line Items]
Marketable securities, amortized cost	25,927
Marketable securities, gross unrealized gains	8
Marketable securities, gross unrealized losses	(1)
Marketable securities, estimated fair value	25,934
U.S. treasury securities
Schedule Of Available For Sale Securities [Line Items]
Marketable securities, amortized cost		1,502
Marketable securities, gross unrealized losses		(1)
Marketable securities, estimated fair value		1,501
U.S. government securities
Schedule Of Available For Sale Securities [Line Items]
Marketable securities, amortized cost	25,743	36,082
Marketable securities, gross unrealized losses	(63)	(101)
Marketable securities, estimated fair value	$ 25,680	$ 35,981

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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-Publisher FASB
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-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
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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).

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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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