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Basis of Presentation of Interim Period Statements - Additional Information (Detail) - USD ($)
 9 Months Ended
Sep. 30, 2016
Sep. 30, 2015
Dec. 31, 2015
Basis Of Presentation Of Interim Period Statements [Line Items]      
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    
Trading securities $ 0   $ 0
Allowance for doubtful accounts 195,000   268,000
Estimate of liability for unpaid safety incentives 25,000,000   $ 21,300,000
Income taxes received $ 1,100,000 $ 9,200,000  
Minimum [Member]      
Basis Of Presentation Of Interim Period Statements [Line Items]      
Restricted cash and investments maturity period 180 days    
Maximum [Member]      
Basis Of Presentation Of Interim Period Statements [Line Items]      
Restricted cash and investments maturity period 2 years