Document and Entity Information - USD ($) $ in Billions	12 Months Ended
	Dec. 31, 2021	Feb. 03, 2022	Jun. 30, 2021
Cover [Abstract]
Document Type	10-K
Document Annual Report	true
Document Transition Report	false
Document Period End Date	Dec. 31, 2021
Entity Interactive Data Current	Yes
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	FY
ICFR Auditor Attestation Flag	true
Amendment Flag	false
Entity Shell Company	false
Entity File Number	1-13998
Entity Registrant Name	Insperity, Inc.
Entity Central Index Key	0001000753
Current Fiscal Year End Date	--12-31
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	76-0479645
Entity Current Reporting Status	Yes
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Small Business	false
Entity Public Float			$ 3.3
Entity Filer Category	Large Accelerated Filer
Entity Emerging Growth Company	false
Entity Address, Address Line One	19001 Crescent Springs Drive
Entity Address, City or Town	Kingwood,
Entity Address, State or Province	TX
Entity Address, Postal Zip Code	77339
City Area Code	281
Local Phone Number	358-8986
Title of 12(b) Security	Common Stock, Par value $0.01 per share
Trading Symbol	NSP
Security Exchange Name	NYSE
Entity Common Stock, Shares Outstanding		38,336,850
Audit Information [Abstract]
Auditor Firm ID	42
Auditor Name	Ernst & Young LLP
Auditor Location	Houston, Texas