| Document and Entity Information Document | Feb. 10, 2022 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Document Period End Date | Feb. 10, 2022 |
| Entity Registrant Name | Insperity, Inc. |
| Entity Incorporation, State or Country Code | DE |
| Entity File Number | 1-13998 |
| Entity Tax Identification Number | 76-0479645 |
| 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 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Entity Emerging Growth Company | false |
| Entity Central Index Key | 0001000753 |
| Amendment Flag | false |
| Common Stock [Member] | |
| Document Information [Line Items] | |
| Title of 12(b) Security | Common Stock, $.01 par value per share |
| Trading Symbol | NSP |
| Security Exchange Name | NYSE |
