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Note 9 - Restricted Net Assets (Details Textual) - USD ($) $ in Thousands | Dec. 31, 2017 | Dec. 31, 2016
--- | --- | ---
The Company's PRC Subsidiaries [Member] |  |
Restricted Net Assets | $ 2,399 | $ 368

X
- Definition Total net assets that cannot be used for operating purposes because of contract or regulatory requirements that are in effect for a period that extends beyond one year. + References No definition available. + Details
Name: | bysi_RestrictedNetAssets
Namespace Prefix: | bysi_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Details
Name: | us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=bysi_TheCompanysPRCSubsidiariesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |