Basis of Presentation and Accounting Policies Earning Per Common Share (Details) - USD ($)	3 Months Ended	6 Months Ended	9 Months Ended
Sep. 30, 2017	Sep. 30, 2016	Jun. 30, 2016	Jun. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Net income (loss) attributable to SEACOR Holdings Inc.	$ 17,561,000	$ (39,803,000)			$ (11,164,000)	$ (122,148,000)
Dilutive Securities, Effect on Basic Earnings Per Share, Options and Restrictive Stock Units	0	0			0	0
Dilutive Securities, Effect on Basic Earnings Per Share, Dilutive Convertible Securities	0	0			0	0
Net Income (Loss) Available to Common Stockholders, Diluted	$ 17,561,000	$ (39,803,000)			$ (11,164,000)	$ (122,148,000)
Weighted Average Number of Shares Outstanding, Basic	17,508,770	16,943,647			17,265,140	16,896,751
Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements	129,054	0			245,420	0
Incremental Common Shares Attributable to Dilutive Effect of Conversion of Debt Securities	0	0			0	0
Weighted Average Number of Shares Outstanding, Diluted	17,637,824	16,943,647			17,510,560	16,896,751
Basic Earnings (Loss) Per Common Share of SEACOR Holdings Inc.	$ 1.00	$ (2.35)			$ (0.65)	$ (7.23)
Diluted Earnings (Loss) Per Common Share of SEACOR Holdings Inc.	$ 1.00	$ (2.35)			$ (0.64)	$ (7.23)
Stock Compensation Plan [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	1,727,132	2,041,652			2,638,753	2,041,652
Three Point Seven Five Percentage Convertible Notes [Member]
Debt Instrument, Interest Rate, Stated Percentage	3.75%				3.75%
Three Point Seven Five Percentage Convertible Notes [Member] \| Convertible Debt Securities [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount		2,243,500				2,243,500
Three Point Zero Percentage Convertible Notes [Member]
Incremental Common Shares Attributable to Dilutive Effect of Conversion of Debt Securities					2,801,147
Debt Instrument, Interest Rate, Stated Percentage	3.00%				3.00%
Three Point Zero Percentage Convertible Notes [Member] \| Convertible Debt Securities [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	2,801,147	1,825,326		1,825,326	2,801,147
Two Point Five Percentage Convertible Notes [Member]
Incremental Common Shares Attributable to Dilutive Effect of Conversion of Debt Securities					1,758,107
Debt Instrument, Interest Rate, Stated Percentage	2.50%				2.50%
Two Point Five Percentage Convertible Notes [Member] \| Convertible Debt Securities [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	1,889,027		2,382,626	2,910,688	2,488,460

Amount of increase (decrease) to net income used for calculating diluted earnings per share (EPS), resulting from the assumed exercise of stock options or restrictive stock units (RSUs).

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The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.

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The amount of net income (loss) for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

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