Commitments and Contingencies (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2015
Commitments and Contingencies Disclosure [Abstract]
Number of states potentially subject to additional FUTA (BCR Add-On) tax	7
FUTA tax associated with BCR Add-On	$ 3.5nsp_FUTAtaxassociatedwithBCRAddOn

The Benefit Cost Ratio Add-On (“BCR”) is an additional Federal Unemployment Tax Act (“FUTA”) tax of 1.5% on the FUTA wage base for employers in states that continue to have outstanding federal unemployment insurance loans beginning with the fifth year in which there is a balance due on the loan. States have the option to apply for a waiver before July 1st of the year in which the BCR is applicable. Fourteen states, including California, are at risk for the BCR in 2014. This is the estimated amount of the tax at the balance sheet date.

No definition available.

Name:	nsp_FUTAtaxassociatedwithBCRAddOn
Namespace Prefix:	nsp_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant