Line of Credit, Additional Credit Available

No definition available.

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

- Definition

Line of Credit Facility, Increase (Decrease) in Borrowing Capacity

+ References

No definition available.

+ Details

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Namespace Prefix:	bbox_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

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- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.16)
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.16)
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 02
-Paragraph 19, 20, 22
-Article 5

+ Details

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

- Definition

Average amount borrowed under the credit facility during the period.

+ References

No definition available.

+ Details

Name:	us-gaap_LineOfCreditFacilityAverageOutstandingAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The effective interest rate during the reporting period.

+ 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 210.5-02.19(b),22(b))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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Balance Type:	na
Period Type:	duration

- Definition

Maximum amount borrowed under the credit facility at any time during the period.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

+ Details

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

- Definition

Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding).

+ References

+ Details

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

- Details

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- Details

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- Details

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- Details

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- Details

Name:	us-gaap_CreditFacilityAxis=bbox_SwingLineLoanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CreditFacilityAxis=us-gaap_LetterOfCreditMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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- Details

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- Details

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Indebtedness (Revolving Credit Agreement) (Details) - USD ($)			12 Months Ended
	May 09, 2016	Apr. 06, 2016	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2015	Apr. 16, 2015	Mar. 23, 2012
Revolving credit agreement
Line of Credit Facility [Line Items]
Maximum borrowing capacity	$ 200,000,000	$ 200,000,000				$ 300,000,000	$ 400,000,000
Increase (decrease) in borrowing capacity with the approval of the lenders		(200,000,000)
Additional capacity available under line of credit agreement	$ 50,000,000	100,000,000
Maximum amount outstanding			$ 150,075,000	$ 183,050,000	$ 206,930,000
Weighted-average amount outstanding			$ 127,727,000	$ 158,256,000	$ 182,149,000
Weighted-average interest rate			2.60%	2.00%	1.70%
Unused commitments			$ 106,750,000
Revolving credit agreement \| Variable component [Member] \| Minimum [Member]
Line of Credit Facility [Line Items]
Basis spread on variable rate	0.00%
Revolving credit agreement \| Variable component [Member] \| Maximum [Member]
Line of Credit Facility [Line Items]
Basis spread on variable rate	1.00%
Swing-line loans [Member]
Line of Credit Facility [Line Items]
Maximum borrowing capacity	$ 15,000,000	25,000,000
Letters of credit [Member]
Line of Credit Facility [Line Items]
Maximum borrowing capacity	$ 25,000,000	$ 25,000,000
Amount outstanding			$ 4,850,000
London Interbank Offered Rate (LIBOR) [Member] \| Revolving credit agreement \| Minimum [Member]
Line of Credit Facility [Line Items]
Basis spread on variable rate		0.875%
London Interbank Offered Rate (LIBOR) [Member] \| Revolving credit agreement \| Maximum [Member]
Line of Credit Facility [Line Items]
Basis spread on variable rate		1.75%
London Interbank Offered Rate (LIBOR) [Member] \| Revolving credit agreement \| Variable component [Member]
Line of Credit Facility [Line Items]
Basis spread on variable rate	1.00%
London Interbank Offered Rate (LIBOR) [Member] \| Revolving credit agreement \| Variable component [Member] \| Minimum [Member]
Line of Credit Facility [Line Items]
Basis spread on variable rate	1.00%
London Interbank Offered Rate (LIBOR) [Member] \| Revolving credit agreement \| Variable component [Member] \| Maximum [Member]
Line of Credit Facility [Line Items]
Basis spread on variable rate	2.00%
Federal Funds Effective Swap Rate [Member] \| Revolving credit agreement \| Variable component [Member]
Line of Credit Facility [Line Items]
Basis spread on variable rate	0.50%
Weighted-average Overnight Federal Fund Rates [Member] \| Revolving credit agreement \| Fixed component [Member]
Line of Credit Facility [Line Items]
Basis spread on variable rate		0.50%
Weighted-average Overnight Federal Fund Rates [Member] \| Revolving credit agreement \| Variable component [Member] \| Minimum [Member]
Line of Credit Facility [Line Items]
Basis spread on variable rate		0.00%
Weighted-average Overnight Federal Fund Rates [Member] \| Revolving credit agreement \| Variable component [Member] \| Maximum [Member]
Line of Credit Facility [Line Items]
Basis spread on variable rate		0.75%