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Significant Accounting Policies (Details) - USD ($) $ in Thousands	1 Months Ended	6 Months Ended
	Apr. 30, 2019	Jun. 30, 2019	Jan. 01, 2019	Dec. 31, 2018
Significant Accounting Policies
Minimum period for maturity dates for short-term investments		90 days
Accumulated deficit		$ (441,380)		$ (435,684)
Lease accounting
Operating lease liabilities		126
Right of use operating assets		126
Operating Lease, Liability, Current		$ 86
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]		Accrued Liabilities, Current
Operating Lease, Liability, Noncurrent		$ 40
Minimum
Lease accounting
Lessee, Operating Lease, Renewal Term		6 months
Maximum
Lease accounting
Lessee, Operating Lease, Renewal Term		2 years 6 months
Guadalupe De Los Reyes, Mexico | Option Agreement Two
Significant Accounting Policies
Value of carrying value for option payment proceeds to be recognized as contract liability	$ 0
Accounting Standards Update 2016-02 | Restatement adjustment
Lease accounting
Operating lease liabilities			$ 186
Right of use operating assets			$ 186

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Term of lessee's operating lease renewal, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

+ References

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Present value of lessee's discounted obligation for lease payments from operating lease.

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Present value of lessee's discounted obligation for lease payments from operating lease, classified as current.

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Present value of lessee's discounted obligation for lease payments from operating lease, classified as noncurrent.

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The cumulative amount of the reporting entity's undistributed earnings or deficit.

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Minimum period for maturity dates relating to short-term investments, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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The amount of the carrying value for the remaining option payment proceeds to be recognized as a contract liability until the title has been transferred to the buyer or the option agreement has been terminated.

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