Unaudited Condensed Consolidated Statements of Income (Loss) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Income Statement [Abstract]
Operating Revenues	$ 36,512	$ 35,667
Costs and Expenses:
Operating	26,307	20,735
Administrative and general	8,611	9,394
Lease expense	1,078	3,325
Depreciation and amortization	14,798	13,362
Costs and expenses	50,794	46,816
Losses on Asset Dispositions and Impairments, Net	(2,273)	(12,572)
Operating Loss	(16,555)	(23,721)
Other Income (Expense):
Interest income	986	662
Interest expense	(8,018)	(7,374)
SEACOR Holdings guarantee fees	(7)	(16)
Derivative gains, net	355	5,114
Foreign currency gains (losses), net	(466)	710
Nonoperating income expense	(7,150)	(904)
Loss from Continuing Operations Before Income Tax Benefit and Equity in Earnings of 50% or Less Owned Companies	(23,705)	(24,625)
Income Tax Expense (Benefit)	(2,688)	(6,662)
Loss from Continuing Operations Before Equity in Earnings of 50% or Less Owned Companies	(21,017)	(17,963)
Equity in Earnings Gains of 50% or Less Owned Companies	4,103	25
Loss from Continuing Operations	(16,914)	(17,938)
Income (Loss) on Discontinued Operations, Net of Tax (see Note 12 and includes gain of $22,756 on the sale of Windcat Workboats)	22,925	(2,054)
Net Income (Loss)	6,011	(19,992)
Net Income (Loss) Attributable to Noncontrolling Interests in Subsidiaries		(4,047)
Net Income (Loss) attributable to SEACOR Marine Holdings Inc.	$ 6,011	$ (15,945)
Basic and Diluted Earnings (Loss) Per Common Share and Warrants of SEACOR Marine Holdings Inc.
Continuing Operations	$ (0.67)	$ (0.58)
Discontinued Operations	0.91	(0.08)
Basic and Diluted Loss Per Common Share and Warrants	$ 0.24	$ (0.66)
Weighted Average Common Stock and Warrants Outstanding:
Basic and diluted shares	25,304,661	23,989,029