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Summary of Operations and Significant Accounting Policies - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014 Segment Unit	Dec. 31, 2013	Dec. 31, 2012	Mar. 01, 2010
Basis Of Presentation Of Interim Period Statements [Line Items]
Restricted capital	$ 58,533,000	$ 11,205,000
Operating and reporting segment	1bbsi_OperatingAndReportingSegment
Revenue recognition professional employer services contracts term	1 year
Professional employer service contract cancellation and termination period	30 days
Cash and cash equivalents, maturity term	3 months
Number of reporting unit	1bbsi_NumberOfReportingUnit
Goodwill and intangible assets impairment	0
Income taxes paid	3,300,000us-gaap_IncomeTaxesPaidNet	9,000,000us-gaap_IncomeTaxesPaidNet	3,300,000us-gaap_IncomeTaxesPaidNet
Anti-dilutive common shares excluded from calculation of diluted loss per share	227,000
California [Member]
Basis Of Presentation Of Interim Period Statements [Line Items]
Revenue from attributable to geographic area	77.00%	74.00%	69.00%
Ecole Insurance Company [Member]
Basis Of Presentation Of Interim Period Statements [Line Items]
Restricted capital				6,100,000
Minimum [Member]
Basis Of Presentation Of Interim Period Statements [Line Items]
Restricted marketable securities maturity period	180 days	180 days
Likelihood of tax benefit being realized upon settlement	50.00%
Minimum [Member] \| AICE [Member]
Basis Of Presentation Of Interim Period Statements [Line Items]
Workers Compensation Coverage Per Occurrence	1,000,000
Maximum [Member]
Basis Of Presentation Of Interim Period Statements [Line Items]
Restricted marketable securities maturity period	2 years	2 years
Maximum [Member] \| AICE [Member]
Basis Of Presentation Of Interim Period Statements [Line Items]
Workers Compensation Coverage Per Occurrence	$ 5,000,000