Short-Term Investments (Details) $ in Thousands	3 Months Ended	12 Months Ended
Mar. 31, 2019 USD ($) instrument	Mar. 31, 2018 USD ($)	Dec. 31, 2018 USD ($) instrument
Short-Term Investments
Amortized Cost	$ 40,012		$ 22,280
Gross Unrealized Losses			(4)
Fair Value	$ 40,012		$ 22,276
Number of short term investments in unrealized loss position \| instrument	1		7
Number of short term investments in an unrealized loss position more than 12 months \| instrument	0
Aggregate fair value of the investments in an unrealized loss position	$ 2,000		$ 7,300
Proceeds from Sale of Short-term Investments	0	$ 0
Corporate debt securities
Short-Term Investments
Amortized Cost	2,012		7,280
Gross Unrealized Losses			(4)
Fair Value	2,012		7,276
Reverse repurchase agreements
Short-Term Investments
Amortized Cost	38,000		15,000
Fair Value	$ 38,000		$ 15,000

The amount of short-term investments at amortized cost.

No definition available.

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- Definition

This item represents the aggregate fair value of short term investments, that have been in a continuous unrealized loss position for less than twelve months.

+ References

No definition available.

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Number of short term investment positions that have been in a continuous unrealized loss position for greater than or equal to a year for which an other-than-temporary impairment (OTTI) has not been recognized in the income statement.

+ References

No definition available.

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- Definition

Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on short-term investments in debt and equity securities.

+ References

No definition available.

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Number of Short term investment positions in a continuous unrealized loss position for which an other-than-temporary impairment (OTTI) has not been recognized in the income statement.

+ References

No definition available.

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The cash inflow from sales of all investments, including securities and other assets, having ready marketability and intended by management to be liquidated, if necessary, within the current operating cycle. Includes cash flows from securities classified as trading securities that were acquired for reasons other than sale in the short-term.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 12
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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.

+ References

No definition available.

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Amount of investments including trading securities, available-for-sale securities, held-to-maturity securities, and short-term investments classified as other and current.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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-Name Accounting Standards Codification
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