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Note 8 - Investments, Including Investments Accounted for Using the Equity Method - Marketable Equity Securities (Details) - USD ($) | Sep. 30, 2019 | Dec. 31, 2018
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Marketable equity securities,Cost | $ 49,941,567 |
Marketable equity securities,Gross Unrealized Loss | 2,925,116 |
Marketable equity securities | $ 52,866,683 |

X
- Definition Amount of accumulated unrealized loss on equity securities. + References No definition available. + Details
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Namespace Prefix: | bomn_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI). + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 45 -Paragraph 1A -URI http://asc.fasb.org/extlink&oid=99377092&loc=SL75136599-209740 + Details
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Balance Type: | debit
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X
- Definition Cost of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI). Excludes equity method investment and investment in equity security without readily determinable fair value. + References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant