Cash and Cash Equivalents and Investments (Details 1) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Cash and Cash Equivalents
Fair Value
Amortized Cost	$ 45,778	$ 80,386
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	45,778	80,386
U.S. Treasury Securities
Fair Value
Amortized Cost	87,334	73,983
Gross Unrealized Gains	35	0
Gross Unrealized Losses	(2)	(9)
Estimated Fair Value	87,367	73,974
Corporate Debt Securities
Fair Value
Amortized Cost	0	5,695
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	(3)
Estimated Fair Value	0	5,692
Total Short-term Investments
Fair Value
Amortized Cost	87,334	79,678
Gross Unrealized Gains	35	0
Gross Unrealized Losses	(2)	(12)
Estimated Fair Value	87,367	79,666
Total Cash and Cash Equivalents and Investments
Fair Value
Amortized Cost	133,112	160,064
Gross Unrealized Gains	35	0
Gross Unrealized Losses	(2)	(12)
Estimated Fair Value	$ 133,145	$ 160,052

Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563

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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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Amount of investment in debt and equity securities categorized neither as trading securities nor held-to-maturity securities and intended be sold or mature one year or operating cycle, if longer.

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