Property and Equipment - Additional Information (Detail) - USD ($) $ in Millions |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2017 |
Dec. 31, 2016 |
Dec. 31, 2015 |
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| Property, Plant and Equipment [Line Items] | |||
| Depreciation expense | $ 0.6 | $ 0.4 | $ 0.5 |
| X | ||||||||||
- Definition The amount of expense recognized in the current period that reflects the allocation of the cost of tangible assets over the assets' useful lives. Includes production and non-production related depreciation. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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| X | ||||||||||
- 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. No definition available.
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