Quarterly report pursuant to Section 13 or 15(d)

Basis of Presentation of Interim Period Statements - Additional Information (Detail)

v3.10.0.1
Basis of Presentation of Interim Period Statements - Additional Information (Detail)
9 Months Ended
Sep. 30, 2018
USD ($)
Company
Sep. 30, 2017
USD ($)
Dec. 31, 2017
USD ($)
Dec. 31, 2016
USD ($)
Organization Consolidation And Presentation Of Financial Statements [Abstract]        
Revenue recognition professional employer service contracts term 1 year      
Professional employer service contract cancellation and termination period 30 days      
Payment term for staffing customers 30 days      
Number of wholly-owned insurance companies | Company 2      
Cash and cash equivalents, maturity term 3 months      
Trading securities $ 0   $ 0  
Allowance for doubtful accounts 482,000   265,000  
Estimate of liability for unpaid safety incentives 28,600,000   28,500,000  
Income taxes paid 100,000 $ 2,500,000    
Interest paid 1,800,000      
Restricted cash and restricted cash equivalents $ 70,149,000 $ 50,200,000 $ 60,370,000 $ 290,600,000