Accounts Receivable (Detail) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Accounts Receivable Additional Disclosures [Abstract]
Accounts Receivable, Net, Current	$ 10,522	$ 6,559
Unbilled accounts receivable	490,533	380,819
Other Receivables	12,251	5,368
Accounts receivable, net	513,306	392,746
Allowance for Doubtful Accounts Receivable, Current	1,000	1,000
Unbilled accounts receivable [Abstract]
Accrued worksite employee payroll cost	409,653	334,836
Unbilled revenues	100,934	81,311
Client Prepayments Included in Cash Balance	(20,054)	(35,328)
Unbilled accounts receivable	$ 490,533	$ 380,819