Deposits (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deposits [Abstract]
Prepaid health insurance	$ 9,000	$ 9,000
Deposits – health insurance	5,300	4,700
Deposits – workers’ compensation	$ 154,215	$ 143,938

Carrying value of amounts transferred to third party workers' compensation insurance providers for security purposes that are expected to be returned or applied towards payment after one year or beyond the operating cycle, if longer.

No definition available.

Name:	nsp_DepositsWorkersCompensation
Namespace Prefix:	nsp_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant