Fair Value Measurement - Summary of Investments (Detail) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Cost	$ 298,683	$ 301,170
Gross Unrealized Gains (Losses)	42	(52)
Recorded Basis	298,725	301,118
Investments Current [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Cost	53,148	107,335
Gross Unrealized Gains (Losses)	0	0
Recorded Basis	53,148	107,335
Investments Current [Member] \| Cash and Cash Equivalents [Member] \| Money Market Funds [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Cost	176	21,312
Gross Unrealized Gains (Losses)	0	0
Recorded Basis	176	21,312
Investments Current [Member] \| Investments [Member] \| Municipal Bonds [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Cost	838	0
Gross Unrealized Gains (Losses)	0	0
Recorded Basis	838	0
Investments Current [Member] \| Investments [Member] \| Corporate Bonds [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Cost	175	0
Gross Unrealized Gains (Losses)	0	0
Recorded Basis	175	0
Investments Current [Member] \| Restricted Cash and Investments [Member] \| Money Market Funds [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Cost	51,959	76,023
Gross Unrealized Gains (Losses)	0	0
Recorded Basis	51,959	76,023
Investments Current [Member] \| Restricted Cash and Investments [Member] \| Certificates of Deposit [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Cost	0	10,000
Gross Unrealized Gains (Losses)	0	0
Recorded Basis	0	10,000
Investments Noncurrent [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Cost	245,535	193,835
Gross Unrealized Gains (Losses)	42	(52)
Recorded Basis	245,577	193,783
Investments Noncurrent [Member] \| Investments [Member] \| Money Market Funds [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Cost	0	4
Gross Unrealized Gains (Losses)	0	0
Recorded Basis	0	4
Investments Noncurrent [Member] \| Investments [Member] \| Municipal Bonds [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Cost	238	3,135
Gross Unrealized Gains (Losses)	0	(3)
Recorded Basis	238	3,132
Investments Noncurrent [Member] \| Investments [Member] \| Corporate Bonds [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Cost	624	2,970
Gross Unrealized Gains (Losses)	1	(24)
Recorded Basis	625	2,946
Investments Noncurrent [Member] \| Restricted Cash and Investments [Member] \| Money Market Funds [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Cost	221,901	175,869
Gross Unrealized Gains (Losses)	0	0
Recorded Basis	221,901	175,869
Investments Noncurrent [Member] \| Restricted Cash and Investments [Member] \| Certificates of Deposit [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Cost	11,776	496
Gross Unrealized Gains (Losses)	0	(1)
Recorded Basis	11,776	495
Investments Noncurrent [Member] \| Restricted Cash and Investments [Member] \| Municipal Bonds [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Cost	2,547	3,613
Gross Unrealized Gains (Losses)	4	(1)
Recorded Basis	2,551	3,612
Investments Noncurrent [Member] \| Restricted Cash and Investments [Member] \| Corporate Bonds [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Cost	3,191	2,996
Gross Unrealized Gains (Losses)	14	(24)
Recorded Basis	3,205	2,972
Investments Noncurrent [Member] \| Restricted Cash and Investments [Member] \| U.S. Treasuries [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Cost	5,258	4,752
Gross Unrealized Gains (Losses)	23	1
Recorded Basis	$ 5,281	$ 4,753

This item represents the cost of debt securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27161-111563

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.2)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount before tax of unrealized gain (loss) in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

No definition available.

+ Details

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

- 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

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

- Definition

Total debt and equity financial instruments including: (1) securities held-to-maturity, (2) trading securities, and (3) securities available-for-sale.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27232-111563

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27161-111563

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.4)
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

+ Details

Name:	us-gaap_MarketableSecurities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=bbsi_MarketableSecuritiesCurrentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByAssetClassAxis=us-gaap_CashAndCashEquivalentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_MoneyMarketFundsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByAssetClassAxis=us-gaap_InvestmentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_MunicipalBondsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_CorporateBondSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByAssetClassAxis=bbsi_RestrictedCashAndInvestmentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_CertificatesOfDepositMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=bbsi_MarketableSecuritiesNoncurrentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_USTreasurySecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: