| Cover - USD ($) | 12 Months Ended | ||
| Dec. 31, 2020 | Feb. 23, 2021 | Jun. 30, 2020 | |
| Cover [Abstract] | |||
| Document Type | 10-K/A | ||
| Document Annual Report | true | ||
| Document Period End Date | Dec. 31, 2020 | ||
| Document Transition Report | false | ||
| Entity File Number | 1-12289 | ||
| Entity Incorporation, State or Country Code | DE | ||
| Entity Tax Identification Number | 13-3542736 | ||
| Entity Address, Address Line One | 2200 Eller Drive, P.O. Box 13038 | ||
| 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 | ||
| Entity Listing, Par Value Per Share | Common Stock, par value $.01 per share | ||
| Trading Symbol | CKH | ||
| Security Exchange Name | NYSE | ||
| Entity Well-known Seasoned Issuer | Yes | ||
| Entity Voluntary Filers | No | ||
| Entity Current Reporting Status | Yes | ||
| Entity Interactive Data Current | Yes | ||
| Entity Filer Category | Large Accelerated Filer | ||
| Entity Small Business | false | ||
| Entity Emerging Growth Company | false | ||
| ICFR Auditor Attestation Flag | true | ||
| Entity Shell Company | false | ||
| Entity Public Float | $ 538,578,460 | ||
| Entity Common Stock, Shares Outstanding | 20,498,564 | ||
| Entity Registrant Name | SEACOR HOLDINGS INC /NEW/ | ||
| Entity Central Index Key | 0000859598 | ||
| Current Fiscal Year End Date | --12-31 | ||
| Document Fiscal Year Focus | 2020 | ||
| Document Fiscal Period Focus | FY | ||
| Amendment Flag | false |
| Cover | 12 Months Ended |
| Dec. 31, 2020 | |
| Cover [Abstract] | |
| Documents Incorporated by Reference | None. |
