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Summary of Significant Accounting Policies - Summary of Derivative Financial Instruments for Non-employee Stock Options (Details) - Fair Value, Measurements, Recurring - Black Scholes Model - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Non-employee Stock Options
Liabilities:
Fair value, liabilities	$ 1,329	$ 2,637
Warrants
Liabilities:
Fair value, liabilities	2,478	6,941
Level 3 | Non-employee Stock Options
Liabilities:
Fair value, liabilities	1,329	2,637
Level 3 | Warrants
Liabilities:
Fair value, liabilities	$ 2,478	$ 6,941

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- Definition

Fair value of financial and nonfinancial obligations.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258

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