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401(k) Plan - Additional Information (Detail) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Schedule Of Sale Of Subsidiary [Abstract] |  |  |
Defined contribution plan, employer discretionary contribution amount | $ 336 | $ 248 | $ 181

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- Definition Schedule Of Sale Of Subsidiary [Abstract] + References No definition available. + Details
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Namespace Prefix: | snd_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Amount of discretionary contributions made by an employer to a defined contribution plan. + References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration