Class action settlement.

No definition available.

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Period Type:	instant

- Definition

Cumulative amount of insurance proceeds received to date for legal expenses related to certain legal actions covered by insurance provider.

+ References

No definition available.

+ Details

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Namespace Prefix:	arb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Cumulated fees and costs incurred from the inception date of certain legal actions.

+ References

No definition available.

+ Details

Name:	arb_CumulativeLegalFeesAndCosts
Namespace Prefix:	arb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

Name:	arb_PrepaidAndOtherCurrentAssetsLineItems
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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The amount recovered from insurance. These recoveries reduce costs and losses that are reported as a separate line item under operating expenses.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 225

-SubTopic 10

-Section S99

-Paragraph 2

-Subparagraph (SX 210.5-03.3)

-URI http://asc.fasb.org/extlink&oid=6880815&loc=d3e20235-122688

+ Details

Name:	us-gaap_InsuranceRecoveries
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Balance Type:	credit
Period Type:	duration

- Definition

The amount of expense provided in the period for legal costs incurred on or before the balance sheet date pertaining to resolved, pending or threatened litigation, including arbitration and mediation proceedings.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 5

-Paragraph 9

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 225

-SubTopic 10

-Section S99

-Paragraph 2

-Subparagraph (SX 210.5-03.3)

-URI http://asc.fasb.org/extlink&oid=6880815&loc=d3e20235-122688

+ Details

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

Prepaid Expenses and Other Current Assets - Additional Information (Detail) (Securities-Law Civil Actions And A Governmental Interaction, USD $) In Millions, unless otherwise specified	9 Months Ended		57 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Feb. 03, 2012
Securities-Law Civil Actions And A Governmental Interaction
Prepaid And Other Current Assets [Line Items]
Class action settlement				$ 7.0
Cumulative legal fees and costs			12.7
Insurance reimbursements	9.7		9.7
Legal fees	0.6	1.3
Estimated Gross insurance recoveries	$ 0.9	$ 1.4