Consolidated Statements Of Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Statement [Abstract]
Operating Revenues	$ 577,891	$ 440,465	$ 521,987
Costs and Expenses:
Operating	360,881	275,255	331,608
Administrative and general	103,106	86,362	101,343
Depreciation and amortization	75,058	62,565	60,356
Total costs and expenses	539,045	424,182	493,307
(Gains) Losses on asset dispositions and impairments, net	11,637	(25,983)	14,609
Operating Income (Loss)	50,483	(9,700)	43,289
Other Income (Expense):
Interest income	8,547	15,641	19,266
Interest expense	(41,530)	(39,804)	(39,151)
Debt extinguishment gains (losses), net	(819)	5,184	(28,497)
Marketable security gains (losses), net	(1,782)	(32,154)	3,746
Derivative gains (losses), net	19,727	(14,131)	1,921
Foreign currency gains (losses), net	323	1,444	(4,725)
Other, net	256	(18,716)	2,400
Nonoperating Income (Expense)	(15,278)	(82,536)	(45,040)
Income (Loss) from Continuing Operations Before Income Tax Expense (Benefit) and Equity in Earnings (Losses) of 50% or Less Owned Companies	35,205	(92,236)	(1,751)
Income Tax Expense (Benefit):
Current	(15,712)	12,207	21,353
Deferred	(51,477)	(48,932)	(21,103)
Income Tax Expense (Benefit)	(67,189)	(36,725)	250
Income (Loss) from Continuing Operations Before Equity in Earnings (Losses) of 50% or Less Owned Companies	102,394	(55,511)	(2,001)
Equity in Earnings (Losses) of 50% or Less Owned Companies	2,952	(21,040)	(49,171)
Income (Loss) from Continuing Operations	105,346	(76,551)	(51,172)
Loss from Discontinued Operations, Net of Tax	(23,637)	(119,221)	(8,678)
Net Income (Loss)	81,709	(195,772)	(59,850)
Net Income Attributable to Noncontrolling Interests in Subsidiaries	20,066	20,125	8,932
Net Income (Loss) attributable to SEACOR Holdings Inc.	61,643	(215,897)	(68,782)
Net Income (Loss) attributable to SEACOR Holdings Inc.:
Continuing Operations	82,849	(94,091)	(53,839)
Discontinued Operations	$ (21,206)	$ (121,806)	$ (14,943)
Basic Earnings (Loss) Per Common Share of SEACOR Holdings Inc.:
Continuing Operations	$ 4.77	$ (5.56)	$ (3.09)
Discontinued Operations	(1.22)	(7.20)	(0.85)
Basic Earnings (Loss) Per Common Share of SEACOR Holdings Inc.	3.55	(12.76)	(3.94)
Diluted Earnings (Loss) Per Common Share of SEACOR Holdings Inc.:
Continuing Operations	4.24	(5.56)	(3.09)
Discontinued Operations	(0.93)	(7.20)	(0.85)
Diluted Earnings (Loss) Per Common Share of SEACOR Holdings Inc.	$ 3.31	$ (12.76)	$ (3.94)
Weighted Average Common Shares Outstanding:
Basic Weighted Average Common Shares Outstanding	17,368,081	16,914,928	17,446,137
Diluted Weighted Average Common Shares Outstanding	22,934,158	16,914,928	17,446,137