| Document and Entity Information | May 25, 2022 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | May 25, 2022 |
| Current Fiscal Year End Date | --12-31 |
| Entity Registrant Name | SYNEOS HEALTH, INC. |
| Entity Central Index Key | 0001610950 |
| Entity Emerging Growth Company | false |
| Entity File Number | 001-36730 |
| Entity Incorporation State Country Code | DE |
| Entity Tax Identification Number | 27-3403111 |
| Entity Address, Address Line One | 1030 Sync Street |
| Entity Address, City or Town | Morrisville |
| Entity Address, State or Province | NC |
| Entity Address, Postal Zip Code | 27560-5468 |
| City Area Code | (919) |
| Local Phone Number | 876-9300 |
| Written Communications | false |
| Soliciting Material | false |
| Pre Commencement Tender Offer | false |
| Pre Commencement Issuer Tender Offer | false |
| Security 12b Title | Class A Common Stock,$0.01 par value per share |
| Trading Symbol | SYNH |
| Security Exchange Name | NASDAQ |
