Deposits (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Deposits [Abstract]
Prepaid health insurance	$ 9,000nsp_PrepaidHealthInsurance	$ 9,000nsp_PrepaidHealthInsurance
Deposits – health insurance	3,700nsp_DepositsHealthInsurance	3,700nsp_DepositsHealthInsurance
Deposits – workers’ compensation	$ 113,934nsp_DepositsWorkersCompensation	$ 81,878nsp_DepositsWorkersCompensation

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