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Revenue Recognition (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018	Dec. 31, 2017
Concentration Risk [Line Items]
Development revenue recognized	$ 737	$ 917	$ 2,983	$ 3,722
Customer Concentration Risk [Member] | Revenue Recognized [Member]
Concentration Risk [Line Items]
Concentration risk percentage	100.00%	100.00%
Customer Concentration Risk [Member] | Accounts Receivable [Member]
Concentration Risk [Line Items]
Concentration risk percentage	100.00%	100.00%

X

- Definition

Aggregate revenue earned during the period from recognition of related party deferred revenue, non-product related activities and revenue earned during the period from non-repayable sum of money awarded to an entity to carry out a specific purpose as provided in grant agreements.

+ References

No definition available.

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- Definition

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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- Definition

For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

+ References

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-Topic 275
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