Long-Term Borrowings (Unsecured Term Loan Due November 2015) (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended	1 Months Ended
Mar. 31, 2013	Nov. 30, 2012 Unsecured Debt [Member]	Mar. 31, 2013 Unsecured Debt [Member]
Debt Instrument [Line Items]
Unsecured term loan		$ 200.0	$ 200.0
Debt instrument, maturity date	November 2015	November 2015
Net proceeds after issuance costs		$ 199.6
Debt instrument variable rate		1.625%
Debt instrument description on variable rate		One-month LIBOR rate plus 1.625%
Fixed interest rate on interest rate swap		2.033%
Premium percentage on principal payment		0.50%

Applicable Interest Rate Spread Above Libor On Variable Rate Debt

No definition available.

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Namespace Prefix:	bmc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Debt Instruments Maturity Date

+ References

No definition available.

+ Details

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Namespace Prefix:	bmc_
Data Type:	us-types:dateStringItemType
Balance Type:	na
Period Type:	duration

- Definition

Net proceeds after original issuance discount and issuance costs.

+ References

No definition available.

+ Details

Name:	bmc_NetProceedsAfterOriginalIssuanceDiscountAndIssuanceCosts
Namespace Prefix:	bmc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Prepayment Premium Percentage Of Principal Amount

+ References

No definition available.

+ Details

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Namespace Prefix:	bmc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The reference rate for the variable rate of the debt instrument, such as LIBOR or the US Treasury rate and the maturity of the reference rate used, such as three months or six months LIBOR.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentDescriptionOfVariableRateBasis
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_DebtInstrumentLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Fixed interest rate related to the interest rate derivative.

+ References

No definition available.

+ Details

Name:	us-gaap_DerivativeFixedInterestRate
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Carrying value as of the balance sheet date of uncollateralized debt obligation (with maturities initially due after one year or beyond the operating cycle if longer), excluding current portion.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.22)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 22

-Article 5

+ Details

Name:	us-gaap_UnsecuredLongTermDebt
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant