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Significant Accounting Policies (Details) $ in Thousands | 12 Months Ended |  |  |
--- | --- | --- | --- | ---
Dec. 31, 2018 USD ($) item | Jan. 01, 2019 USD ($) | Jan. 01, 2018 USD ($) | Dec. 31, 2017 USD ($)
Significant Accounting Policies |  |  |  |
Minimum period for maturity dates for short-term investments | 90 days |  |  |
Accumulated deficit | $ (435,684) |  |  | $ (426,968)
Revenue recognition |  |  |  |
Number of projects currently in production that could provide future variable consideration | item | 0 |  |  |
Difference between Revenue Guidance in Effect before and after Topic 606 | Accounting Standards Update 2014-09 |  |  |  |
Significant Accounting Policies |  |  |  |
Accumulated deficit |  |  | $ 0 |
Restatement adjustment | Accounting Standards Update 2016-02 |  |  |  |
Lease accounting |  |  |  |
Operating lease liabilities |  | $ 185 |  |
Right of use operating assets |  | $ 185 |  |
Option Agreement Two | Guadalupe De Los Reyes, Mexico |  |  |  |
Revenue recognition |  |  |  |
Value of carrying value for option payment proceeds to be recognized as contract liability | $ 0 |  |  |

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