The fair value of equity method investments acquired and unpaid.

No definition available.

Name:	bgm_FairValueOfEquityMethodInvestmentsAcquiredAndUnpaid
Namespace Prefix:	bgm_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Number of shares of equity interest issued or issuable by acquirer as part of consideration transferred in business combination.

+ References

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+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Per share price of saleable stock paid or offered to be paid by acquirer in business combination.

+ References

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+ Details

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Namespace Prefix:	us-gaap_
Data Type:	dtr-types:perShareItemType
Balance Type:	na
Period Type:	instant

- Definition

This element represents the aggregate cost of investments accounted for under the equity method of accounting.

+ References

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+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

+ References

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+ Details

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Balance Type:	na
Period Type:	instant

- Details

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Data Type:	na
Balance Type:
Period Type:

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BusinessAcquisitionAxis=bgm_HmManagementCompanyLimitedMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=bgm_CaihouCapitalShenzhenGroupCo.LtdMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Consolidated Statements of Cash flows (Parenthetical)	12 Months Ended
Consolidated Statements of Cash flows (Parenthetical)	Sep. 30, 2025 USD ($) $ / shares shares	Sep. 30, 2024 CNY (¥)	Sep. 30, 2024 USD ($)
Total consideration \| $	$ 12,159,595
AI Solutions and Insurance Business, YX Management Company Limited and Yang Lou Dong \| Class A ordinary shares
Number of shares issued \| shares	155,660,951
Share price (in dollar per share) \| $ / shares	$ 2
HM Management Company Limited \| Class A ordinary shares
Number of shares issued \| shares	16,663,427
Share price (in dollar per share) \| $ / shares	$ 2.5
Caihou Capital (Shenzhen) Group Co., Ltd
Unpaid equity investment		¥ 15,000,000	$ 2,107,407
Ownership interest acquired (in percent)		25.00%
Total consideration \| ¥		¥ 25,000,000