Workers Compensation Assets and Liabilities - Additional Information (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Insurance [Abstract]
Collateral held by insurance carriers	$ 68,800	$ 65,600
Collateral paid to carriers and offset against loss reserves	$ (27,412)	$ (31,611)

Liability for Unpaid Claims and Claims Adjustment Expense, Collateral

No definition available.

Name:	tnet_LiabilityforUnpaidClaimsandClaimsAdjustmentExpenseCollateral
Namespace Prefix:	tnet_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant