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Summary of Operations and Significant Accounting Policies - Additional Information (Detail)
12 Months Ended
Dec. 31, 2021
USD ($)
Branch
Segment
Company
Dec. 31, 2020
USD ($)
Dec. 31, 2019
USD ($)
Dec. 31, 2018
USD ($)
Basis Of Presentation Of Interim Period Statements [Line Items]        
Number Of Branch Offices | Branch 50      
Number of operating segment | Segment 1      
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      
Allowance for doubtful accounts $ 460,000 $ 757,000 $ 888,000 $ 533,000
Number of reporting units | Segment 1      
Goodwill and intangible assets impairment $ 0      
Impairment of long lived asset 0      
Residual value of leased asset 3,700,000      
Estimate of liability for unpaid safety incentives 4,300,000 18,800,000    
Income taxes paid $ 4,700,000 $ 8,500,000 $ 15,400,000  
Minimum [Member]        
Basis Of Presentation Of Interim Period Statements [Line Items]        
Likelihood of tax benefit being realized upon settlement 50.00%      
California [Member] | Revenue [Member] | Geographic Concentration Risk [Member]        
Basis Of Presentation Of Interim Period Statements [Line Items]        
Percentage of revenue attributable to geographic area 73.00% 75.00% 77.00%