Document and Entity Information - shares	6 Months Ended
	Jun. 30, 2018	Jul. 25, 2018
Entity Information [Line Items]
Entity Registrant Name	INSPERITY, INC.
Entity Central Index Key	0001000753
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		41,923,815
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	Q2
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Jun. 30, 2018