| Document and Entity Information | Apr. 15, 2021 |
| Cover [Abstract] | |
| Entity Registrant Name | SEACOR HOLDINGS INC /NEW/ |
| Amendment Flag | false |
| Entity Central Index Key | 0000859598 |
| Current Fiscal Year End Date | --12-31 |
| Document Type | 8-K |
| Document Period End Date | Apr. 15, 2021 |
| Entity Incorporation State Country Code | DE |
| Entity File Number | 1-12289 |
| Entity Tax Identification Number | 13-3542736 |
| Entity Address, Address Line One | 2200 Eller Drive |
| Entity Address, City or Town | Fort Lauderdale |
| Entity Address, State or Province | FL |
| Entity Address, Postal Zip Code | 33316 |
| City Area Code | (954) |
| Local Phone Number | 523-2200 |
| Written Communications | false |
| Soliciting Material | false |
| Pre Commencement Tender Offer | false |
| Pre Commencement Issuer Tender Offer | false |
| Security 12b Title | Common Stock, $0.01 par value |
| Trading Symbol | CKH |
| Security Exchange Name | NYSE |
| Entity Emerging Growth Company | false |
