| Cover | May 04, 2021 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | May 4, 2021 |
| Entity File Number | 001-38980 |
| Entity Registrant Name | AssetMark Financial Holdings, Inc. |
| Entity Central Index Key | 0001591587 |
| Entity Tax Identification Number | 30-0774039 |
| Entity Incorporation, State or Country Code | DE |
| Entity Address, Address Line One | 1655 Grant Street |
| Entity Address, Address Line Two | 10th Floor |
| Entity Address, City or Town | Concord |
| Entity Address, State or Province | CA |
| Entity Address, Postal Zip Code | 94520 |
| City Area Code | 925 |
| Local Phone Number | 521-2200 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common stock, $0.001 par value |
| Trading Symbol | AMK |
| Security Exchange Name | NYSE |
| Entity Emerging Growth Company | true |
| Elected Not To Use the Extended Transition Period | false |
