Nature Of Operations And Accounting Policies (Schedule Of Earnings Per Share) (Details) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 01, 2015	Nov. 13, 2013	Dec. 11, 2012
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net Income (Loss) attributable to SEACOR Holdings Inc.	$ (93,749,000)	$ (39,803,000)	$ (55,159,000)	$ (27,186,000)	$ (56,865,000)	$ 6,965,000	$ 687,000	$ (19,569,000)	$ (215,897,000)	$ (68,782,000)	$ 100,132,000
Dilutive Securities, Effect on Basic Earnings Per Share, Options and Restrictive Stock Units									0	0	0
Dilutive Securities, Effect on Basic Earnings Per Share, Dilutive Convertible Securities									0	0	21,156,000
Net Income (Loss) Available to Common Stockholders, Diluted									$ (215,897,000)	$ (68,782,000)	$ 121,288,000
Average o/s Shares, Basic									16,914,928	17,446,137	19,336,280
Incremental Common Shares Attributable to Share-based Payment Arrangements									0	0	403,194
Convertible Securities									0	0	6,025,851
Average o/s Shares, Diluted									16,914,928	17,446,137	25,765,325
Basic Earnings (Loss) Per Common Share of SEACOR Holdings Inc.	$ (5.52)	$ (2.35)	$ (3.26)	$ (1.62)	$ (3.36)	$ 0.40	$ 0.04	$ (1.10)	$ (12.76)	$ (3.94)	$ 5.18
Diluted Earnings (Loss) Per Common Share of SEACOR Holdings Inc.	$ (5.52)	$ (2.35)	$ (3.26)	$ (1.62)	$ (3.36)	$ 0.40	$ 0.04	$ (1.10)	$ (12.76)	$ (3.94)	$ 4.71
Two Point Five Percentage Convertible Notes [Member]
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Convertible Securities									1,885,772
Debt Instrument, Interest Rate, Stated Percentage	2.50%								2.50%					2.50%
Three Point Zero Percentage Convertible Notes [Member]
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Convertible Securities									1,825,326
Debt Instrument, Interest Rate, Stated Percentage	3.00%								3.00%				3.00%
Three Point Seven Five Percentage Convertible Notes [Member]
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Convertible Securities									2,243,500
Debt Instrument, Interest Rate, Stated Percentage												3.75%
Stock Compensation Plan [Member]
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount									2,020,677	2,078,777	407,698
Convertible Debt Securities [Member] | Two Point Five Percentage Convertible Notes [Member]
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount									2,664,208	4,148,327
Convertible Debt Securities [Member] | Three Point Zero Percentage Convertible Notes [Member]
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount									1,825,326	1,825,326
Convertible Debt Securities [Member] | Three Point Seven Five Percentage Convertible Notes [Member]
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount									2,243,500	190,544