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v3.21.1

Proxy Contest Costs and Recoveries (Details) - USD ($) $ in Thousands | 3 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2021 | Mar. 31, 2020 | Dec. 31, 2020
Other Income and Expenses [Abstract] |  |  |
Proxy contest costs and recoveries | $ (464) | $ 0 | $ 3,100
Insurance recoveries, receivable | $ 500 |  |

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- Definition Proxy Contest Costs (Recoveries) + References No definition available. + Details
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Namespace Prefix: | synl_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Amount of receivable related to a loss contingency accrual. For example, an insurance recovery receivable. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 460 -SubTopic 10 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=121555522&loc=d3e12053-110248 + Details
Name: | us-gaap_LossContingencyReceivable
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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