Basis of Presentation (Details)	3 Months Ended
Mar. 31, 2013	Mar. 31, 2012
Basis of Presentation [Abstract]
Percentage of PEO revenues from the Company's Texas markets (in hundredths)	25.00%	26.00%
Percentage of PEO revenues from the Company's California markets (in hundredths)	17.00%	17.00%

A presentation of the revenue percentage from the state of California.

No definition available.

Name:	nsp_PercentageOfRevenuesFromCompanyCaliforniaMarkets
Namespace Prefix:	nsp_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration