Condensed Consolidated Statements Of Income - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Income Statement [Abstract]
Operating Revenues	$ 175,414	$ 200,658	$ 540,295	$ 607,205
Costs and Expenses:
Operating	128,546	147,386	400,752	437,368
Administrative and general	24,560	24,923	76,785	78,383
Depreciation and amortization	17,306	16,975	52,620	51,120
Total costs and expenses	170,412	189,284	530,157	566,871
Gains on Asset Dispositions, Net	618	1,145	9,200	2,259
Operating Income	5,620	12,519	19,338	42,593
Other Income (Expense):
Interest income	1,425	2,198	4,544	5,983
Interest expense	(3,938)	(4,816)	(12,587)	(14,832)
Debt extinguishment gains (losses), net	(254)	(777)	1,348	(2,073)
Marketable security gains (losses), net	951	144	(567)	16,496
Foreign currency losses, net	(203)	(1,877)	(3,042)	(1,663)
Other, net	2,242	505	2,992	(114)
Total Other Nonoperating Expense	223	(4,623)	(7,312)	3,797
Income Before Income Tax Expense (Benefit) and Equity in Losses of 50% or Less Owned Companies	5,843	7,896	12,026	46,390
Income Tax Expense (Benefit)	1,552	1,417	(9,384)	7,012
Income Before Equity in Losses of 50% or Less Owned Companies	4,291	6,479	21,410	39,378
Equity in Losses of 50% or Less Owned Companies, Net of Tax	(1,102)	(618)	(8,877)	(3,448)
Net Income	3,189	5,861	12,533	35,930
Net Income (Loss) Attributable to Noncontrolling Interests in Subsidiaries	(1)	(544)	(8)	7,239
Net Income Attributable to SEACOR Holdings Inc.	$ 3,190	$ 6,405	$ 12,541	$ 28,691
Basic Earnings Per Common Share of SEACOR Holdings Inc. (in dollars per share)	$ 0.16	$ 0.33	$ 0.63	$ 1.54
Diluted Earnings Per Common Share of SEACOR Holdings Inc. (in dollars per share)	$ 0.16	$ 0.32	$ 0.63	$ 1.48
Weighted Average Common Shares Outstanding:
Basic (in shares)	19,995,413	19,322,423	19,975,635	18,618,613
Diluted (in shares)	20,017,551	20,738,919	19,993,982	19,984,302