Marketable Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Short-term investments
Amortized Cost	$ 97,093
Unrealized Gains	17
Unrealized Losses	(7)
Aggregate Fair Value	97,103	$ 0
Cash equivalents
Carrying Value	22,858
Total marketable securities, Amortized Cost	119,951
Total marketable securities, Unrealized Gains	17
Total marketable securities, Unrealized Losses	(7)
Total marketable securities, Aggregate Fair Value	119,961
U.S. treasury securities
Short-term investments
Amortized Cost	65,491
Unrealized Gains	2
Unrealized Losses	(4)
Aggregate Fair Value	65,489
Cash equivalents
Carrying Value	1,000
Corporate bonds
Short-term investments
Amortized Cost	19,708
Unrealized Gains	15
Unrealized Losses	(3)
Aggregate Fair Value	19,720
Commercial paper
Short-term investments
Amortized Cost	11,894
Unrealized Gains	0
Unrealized Losses	0
Aggregate Fair Value	11,894
Cash equivalents
Carrying Value	6,635
Money market funds
Cash equivalents
Carrying Value	$ 15,223	$ 22,100

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Marketable Securities, Accumulated Gross Unrealized Loss, Before Tax

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Total amortized cost for marketable securities included in cash equivalents and investments.

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Total aggregate fair value for marketable securities included in cash equivalents and investments.

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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 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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