Basis of Presentation of Interim Period Statements [Line Items]

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- Definition

Cash and cash equivalents maximum maturity period.

+ References

No definition available.

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- Definition

Customer incentive liability.

+ References

No definition available.

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- Definition

Estimate of liability for unpaid safety incentives.

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No definition available.

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- Definition

Likelihood of tax benefit being realized upon settlement percent.

+ References

No definition available.

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- Definition

Number of branch offices.

+ References

No definition available.

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- Definition

Number of wholly owned insurance companies.

+ References

No definition available.

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- Definition

Payment term for staffing customers.

+ References

No definition available.

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- Definition

Period for cancellation or termination of PEO service contract.

+ References

No definition available.

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- Definition

Revenue recognition PEO service contract minimum term.

+ References

No definition available.

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- Definition

Amount of allowance for credit loss on accounts receivable.

+ References

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- Definition

For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

+ References

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- Definition

Total loss recognized during the period from the impairment of goodwill plus the loss recognized in the period resulting from the impairment of the carrying amount of intangible assets, other than goodwill.

+ References

No definition available.

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- Definition

The amount of cash paid during the current period to foreign, federal, state, and local authorities as taxes on income.

+ References

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- Definition

Number of operating segments. An operating segment is a component of an enterprise: (a) that engages in business activities from which it may earn revenues and incur expenses (including revenues and expenses relating to transactions with other components of the same enterprise), (b) whose operating results are regularly reviewed by the enterprise's chief operating decision maker to make decisions about resources to be allocated to the segment and assess its performance, and (c) for which discrete financial information is available. An operating segment may engage in business activities for which it has yet to earn revenues, for example, start-up operations may be operating segments before earning revenues.

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- Definition

Number of reporting units tested for impairment of goodwill. A reporting unit is an operating segment or one level below an operating segment.

+ References

No definition available.

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Summary of Operations and Significant Accounting Policies - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2020 USD ($) Branch Segment Company	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Basis Of Presentation Of Interim Period Statements [Line Items]
Number Of Branch Offices \| Branch	56
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	$ 757,000	$ 888,000	$ 533,000	$ 265,000
Number of reporting units \| Segment	1
Goodwill and intangible assets impairment	$ 0
Estimate of liability for unpaid safety incentives	18,800,000	28,000,000.0
One-time customer Incentive	0	2,400,000	9,800,000
Income taxes paid	$ 8,500,000	$ 15,400,000	$ 1,800,000
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	75.00%	77.00%	79.00%