Basis of Presentation of Interim Period Statements - Additional Information (Detail)	6 Months Ended
	Jun. 30, 2018 USD ($) Company	Jun. 30, 2017 USD ($) shares	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	432,000		265,000
Estimate of liability for unpaid safety incentives	28,100,000		28,500,000
Income taxes paid	100,000	$ 2,400,000
Interest paid	1,800,000
Potential common shares excluded from calculation of diluted loss per share | shares		294,169
Restricted cash and restricted cash equivalents	$ 24,862,000	$ 95,200,000	$ 60,370,000	$ 290,600,000