Defined Contribution Plan - Additional Information (Detail) - USD ($) $ in Millions |
12 Months Ended | ||
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Dec. 31, 2017 |
Dec. 31, 2016 |
Dec. 31, 2015 |
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| Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] | |||
| Benefit plan related expenses | $ 0.4 | $ 0.3 | $ 0.2 |
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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. No definition available.
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| X | ||||||||||
- Definition Amount of cost for defined contribution plan. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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