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Credit Losses (Tables) | 9 Months Ended
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Sep. 30, 2020
Receivables [Abstract] |
Allowance For Credit Losses On Trade Accounts Receivable | The following is a rollforward of the allowances for credit losses related to trade accounts receivable for the nine months ended September 30, 2020:
|  | September 30, 2020
Balance at beginning of period |  | $ | 1.2 |
Current period provision |  | 1.4 |
Write-offs |  | (0.6) |
Balance at end of period |  | $ | 2.0 |

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- Definition Allowance For Credit Losses On Trade Accounts Receivable [Table Text Block] + References No definition available. + Details
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Namespace Prefix: | syx_
Data Type: | nonnum:textBlockItemType
Balance Type: | na
Period Type: | duration

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- References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration