SEACOR Marine (SMHI) 10-K 12 Mar 21 2020 FY Annual report Financial data

Document And Entity Information

Document And Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Mar. 01, 2021	Jun. 30, 2020
Cover [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2020
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
Trading Symbol	SMHI
Entity Registrant Name	SEACOR Marine Holdings Inc.
Entity Central Index Key	0001690334
Current Fiscal Year End Date	--12-31
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
ICFR Auditor Attestation Flag	false
Entity Ex Transition Period	true
Entity Shell Company	false
Title of 12(b) Security	Common stock
Security Exchange Name	NYSE
Entity File Number	1-37966
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	47-2564547
Entity Address, Address Line One	12121 Wickchester Lane
Entity Address, Address Line Two	Suite 500
Entity Address, City or Town	Houston
Entity Address, State or Province	TX
Entity Address, Postal Zip Code	77079
City Area Code	346
Local Phone Number	980-1700
Document Annual Report	true
Document Transition Report	false
Entity Common Stock, Shares Outstanding		23,416,567
Entity Public Float			$ 52
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Documents Incorporated by Reference	Portions of the Registrant’s definitive proxy statement for its 2021 Annual Meeting of Stockholders to be filed with the Securities and Exchange Commission (the "SEC") pursuant to Regulation 14A within 120 days after the end of the Registrant’s last fiscal year is incorporated by reference into Part III of this Annual Report on Form 10-K.

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands		Dec. 31, 2020	Dec. 31, 2019
Current Assets:
Cash and cash equivalents		$ 32,666	$ 81,382
Restricted cash		3,352	3,104
Receivables:
Trade, net of allowance for credit loss reserve of $582 and $455 in 2020 and 2019, respectively		45,325	43,050
Other		10,924	18,239
Receivables from SEACOR Holdings		18,832
Tax Receivable		13,556
Inventories		576	1,228
Prepaid expenses and other		3,230	1,940
Assets held for sale		50,235	45,718
Total current assets		178,696	194,661
Property and Equipment:
Historical cost	[1]	1,012,873	899,024
Accumulated depreciation		(291,538)	(308,917)
Property and equipment		721,335	590,107
Construction in progress		32,327	70,806
Net property and equipment		753,662	660,913
Right-of-Use Asset - Operating Leases		7,134	16,537
Right-of-Use Asset - Finance Leases		129
Investments, at Equity, and Advances to 50% or Less Owned Companies		75,308	120,831
Construction Reserve Funds			12,893
Other Assets		2,734	3,358
Total assets		1,017,663	1,009,193
Current Liabilities:
Current portion of operating lease liabilities		7,030	14,896
Current portion of finance lease liabilities		36
Current portion of long-term debt
Recourse		26,734	17,802
Non Recourse		5,643
Accounts payable and accrued expenses		29,967	24,598
Due to SEACOR Holdings			74
Accrued wages and benefits		1,744	1,545
Accrued interest		1,664	729
Accrued capital, repair and maintenance expenditures		11,328	15,978
Deferred and Unearned revenues		4,452	5,296
Accrued insurance deductibles and premiums		2,274	3,564
Accrued professional fees		975	871
Derivatives		4,591	2,925
Other current liabilities		4,439	4,479
Liabilities associated with assets held for sale		30,927	27,540
Total current liabilities		131,804	120,297
Long-Term Operating Lease Liabilities		4,345	9,255
Long-Term Finance Lease Liabilities		105
Long-Term Debt
Recourse		328,690	239,939
Non Recourse		111,820	115,775
Conversion Option Liability on Convertible Senior Notes		2	5,205
Deferred Income Taxes		35,822	33,564
Deferred Gains and Other Liabilities		3,239	6,234
Total liabilities		615,827	530,269
SEACOR Marine Holdings Inc. stockholders' equity:
Preferred stock, $.01 par value, 10,000,000 shares authorized; none issued nor outstanding
Common stock, $.01 par value, 60,000,000 shares authorized; 23,504,050 and 21,928,674 shares issued in 2020 and 2019, respectively		235	219
Additional paid-in capital		451,179	429,318
Retained earnings		(51,839)	27,076
Shares held in treasury of 73,284 and 47,185 in 2020 and 2019, respectively, at cost		(848)	(669)
Accumulated other comprehensive loss, net of tax		2,790	1,548
Total stockholders equity		401,517	457,492
Noncontrolling interests in subsidiaries		319	21,432
Total equity		401,836	478,924
Total liabilities and equity		$ 1,017,663	$ 1,009,193
[1]	Includes property and equipment acquired in business acquisitions at acquisition date fair value, and net of the impact of recognized impairment charges.

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Statement Of Financial Position [Abstract]
Trade receivables, allowance for credit loss	$ 582	$ 455
Preferred stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock, shares authorized (in shares)	10,000,000	10,000,000
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	60,000,000	60,000,000
Common stock, shares issued (in shares)	23,504,050	21,928,674
Shares held in treasury (in shares)	73,284	47,185

Consolidated Statements of Loss

Consolidated Statements of Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Statement [Abstract]
Operating Revenues	$ 141,837	$ 174,453	$ 179,161
Costs and Expenses:
Operating	91,145	109,523	119,587
Administrative and general	40,051	39,791	41,616
Lease expense	7,525	15,840	12,964
Depreciation and amortization	57,167	57,166	61,419
Costs and expenses	195,888	222,320	235,586
Losses on Asset Dispositions and Impairments, Net	(17,588)	(6,461)	(11,989)
Operating Loss	(71,639)	(54,328)	(68,414)
Other Income (Expense):
Interest income	1,273	1,389	1,171
Interest expense	(30,691)	(28,956)	(26,726)
SEACOR Holdings guarantee fees	(47)	(108)	(29)
Loss on Debt Extinguishment			(638)
Derivative gains, net	4,310	71	2,854
Foreign currency losses, net	(1,294)	(2,541)	(1,328)
Other, net	(19)	(1)	677
Nonoperating income expense	(26,468)	(30,146)	(24,019)
Loss from Continuing Operations Before Tax Benefit and Equity in Losses of 50% or Less Owned Companies	(98,107)	(84,474)	(92,433)
Income Tax (Benefit) Expense:
Current	(25,182)	4,921	9,297
Deferred	2,258	(12,890)	(22,760)
Income Tax (Benefit) Expense	(22,924)	(7,969)	(13,463)
Loss Before Equity in Losses of 50% or Less Owned Companies	(75,183)	(76,505)	(78,970)
Equity in Losses of 50% or Less Owned Companies, Net of Tax	(8,163)	(14,459)	(4,009)
Loss from Continuing Operations	(83,346)	(90,964)	(82,979)
Income (Loss) on Discontinued Operations, Net of Tax	364	(7,731)	927
Net Loss	(82,982)	(98,695)	(82,052)
Net Loss attributable to Noncontrolling Interests in Subsidiaries	(4,067)	(5,858)	(4,444)
Net Loss attributable to SEACOR Marine Holdings Inc.	$ (78,915)	$ (92,837)	$ (77,608)
Basic and Diluted (Loss) Income Per Common Share and Warrants of SEACOR Marine Holdings Inc.
Continuing operations	$ (3.20)	$ (3.62)	$ (3.74)
Discontinued operations	0.02	(0.33)	0.04
Basic and Diluted Income (Loss) Per Common Share and Warrants	$ (3.18)	$ (3.95)	$ (3.70)
Weighted Average Common Shares and Warrants Outstanding:
Basic and diluted shares	24,785,744	23,513,925	20,926,307

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Net Loss	$ (82,982)	$ (98,695)	$ (82,052)
Other Comprehensive Income (Loss):
Foreign currency translation gains (losses), net	2,112	20,157	(2,365)
Derivative losses on cash flow hedges	(2,139)	(1,901)	(1,939)
Other comprehensive income	1,242	18,163	(4,349)
Income tax benefit (expense)		173	(46)
Other comprehensive income, net	1,242	18,336	(4,395)
Comprehensive Loss	(81,740)	(80,359)	(86,447)
Comprehensive Loss attributable to Noncontrolling Interests in Subsidiaries	(4,067)	(5,858)	(4,544)
Comprehensive Loss attributable to SEACOR Marine Holdings Inc.	(77,673)	(74,501)	(81,903)
Interest Expense
Other Comprehensive Income (Loss):
Reclassification of derivative losses on cash flow hedges	1,425	552	31
Equity Method Investments
Other Comprehensive Income (Loss):
Reclassification of derivative losses on cash flow hedges	$ (156)	$ (645)	$ (76)

Consolidated Statements of Co_2

Consolidated Statements of Comprehensive Loss (Parenthetical)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Statement Of Income And Comprehensive Income [Abstract]
Reclassification of derivative losses on cash flow hedges to equity in losses	50.00%	50.00%	50.00%

Consolidated Statements of Chan

Consolidated Statements of Changes In Equity - USD ($)	Total	Previously Reported [Member]	Revision of Prior Period, Accounting Standards Update, Adjustment [Member]	Common Stock [Member]	Common Stock [Member]Previously Reported [Member]	Additional Paid-in Capital [Member]	Additional Paid-in Capital [Member]Previously Reported [Member]	Treasury Stock [Member]	Treasury Stock [Member]Previously Reported [Member]	Retained Earnings [Member]	Retained Earnings [Member]Previously Reported [Member]	Retained Earnings [Member]Revision of Prior Period, Accounting Standards Update, Adjustment [Member]	Accumulated Other Comprehensive Loss [Member]	Accumulated Other Comprehensive Loss [Member]Previously Reported [Member]	Non-Controlling Interests In Subsidiaries [Member]	Non-Controlling Interests In Subsidiaries [Member]Previously Reported [Member]
Balance at Dec. 31, 2017	$ 511,097,000			$ 177,000		$ 303,996,000				$ 204,442,000			$ (12,493,000)		$ 14,975,000
Balance (in shares) at Dec. 31, 2017				17,675,356
Issuance of Common Stock	42,996,000			$ 23,000		42,973,000
Issuance of Common Stock (in shares)				2,291,084
Issuance of Warrants	62,809,000					62,809,000
Amortization of employee share awards	3,494,000					3,494,000
Exercise of options	833,000			$ 1,000		832,000
Exercise of options (in shares)				66,625
Exercise of Warrants				$ 3,000				$ (3,000)
Exercise of Warrants (in shares)				289,442				108
Restricted stock vesting	(88,000)							$ (88,000)
Restricted stock vesting (in shares)				116,701				3,899
Director share awards	893,000					893,000
Acquisition of consolidated joint venture	(12,037)														(12,037,000)
Issuance of noncontrolling interests	31,010,000					375,000									31,010,000
Net Loss	(82,052,000)									(77,608,000)					(4,444,000)
Other comprehensive (income) loss	(4,395,000)												(4,295,000)		(100,000)
Balance at Dec. 31, 2018	565,351,000	$ 554,935,000	$ 10,416,000	$ 204,000	$ 204,000	415,372,000	$ 415,372,000	$ (91,000)	$ (91,000)	137,250,000	$ 126,834,000	$ 10,416,000	(16,788,000)	$ (16,788,000)	29,404,000	$ 29,404,000
Balance (in shares) at Dec. 31, 2018				20,439,208	20,439,208			4,007	4,007
Issuance of Common Stock	6,596,000			$ 7,000		6,589,000
Issuance of Common Stock (in shares)				653,872
Restricted stock grants	2,000			$ 2,000
Restricted stock grants (in shares)				245,400
Cancellation of restricted stock grants (in shares)				(2,200)
Amortization of employee share awards	5,046,000					5,046,000
Exercise of options	$ 1,421,000			$ 1,000		1,420,000
Exercise of options (in shares)	113,750			113,750
Exercise of Warrants	$ 3,000			$ 4,000				$ (1,000)
Exercise of Warrants (in shares)				444,391
Restricted stock vesting	(579,000)					(2,000)		$ (577,000)
Restricted stock vesting (in shares)				(43,129)				43,129
Director share awards	894,000			$ 1,000		893,000
Director share awards (in shares)				30,197				49
Acquisition of consolidated joint venture	(2,114,000)														(2,114,000)
Sale of Standby Safety Fleet	(17,399,000)									(17,399,000)
Dissolution of an entity	62,000									62,000
Net Loss	(98,695,000)									(92,837,000)					(5,858,000)
Other comprehensive (income) loss	18,336,000												18,336,000
Balance at Dec. 31, 2019	$ 478,924,000			$ 219,000		429,318,000		$ (669,000)		27,076,000			1,548,000		21,432,000
Balance (in shares) at Dec. 31, 2019	21,928,674			21,881,489				47,185
Restricted stock grants	$ 3,000			$ 3,000
Restricted stock grants (in shares)				289,452
Cancellation of grants and options	101,000					101,000
Cancellation of grants and options (in shares)				(12,650)
Amortization of employee share awards	$ 3,969,000					3,969,000
Exercise of options (in shares)	0
Exercise of Warrants	$ 2,000			$ 3,000				$ (1,000)
Exercise of Warrants (in shares)				338,320				354
Restricted stock vesting	(178,000)							$ (178,000)
Restricted stock vesting (in shares)				(25,745)				25,745
Director share awards	755,000			$ 1,000		754,000
Director share awards (in shares)				59,900
Acquisition of consolidated joint venture				$ 9,000		17,037,000									(17,046,000)
Acquisition of consolidated joint venture (in shares)				900,000
Net Loss	(82,982,000)									(78,915,000)					(4,067,000)
Other comprehensive (income) loss	1,242,000												1,242,000
Balance at Dec. 31, 2020	$ 401,836,000			$ 235,000		$ 451,179,000		$ (848,000)		$ (51,839,000)			$ 2,790,000		$ 319,000
Balance (in shares) at Dec. 31, 2020	23,504,050			23,430,766				73,284

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Cash Flows from Continuing Operating Activities:
Net Loss	$ (83,346)	$ (100,070)	$ (82,979)
Adjustments to reconcile net loss to net cash (used in) provided by operating activities:
Depreciation and amortization	57,167	57,166	61,419
Deferred financing cost amortization	1,107	1,055	1,886
Amortization of deferred gains against charter expense			(8,037)
Amortization of employee share awards	4,069	5,046	3,494
Restricted stock vesting	(178)	(577)	(88)
Director share awards	755	894	893
Debt discount amortization	6,672	5,662	5,348
Provision for expected credit losses	230	(404)	(880)
Losses from equipment sales, retirements or impairments	17,588	6,461	11,989
Loss from sale of Boston Putford Offshore Safety		9,106
Gain from other sales			(428)
Derivative gains	(4,310)	(71)	(2,854)
Cash settlement payments on derivative transactions, net	(1,331)	(482)	1,407
Currency losses	1,294	2,541	1,328
Deferred	2,258	(12,890)	(22,760)
Equity losses	8,163	14,459	4,009
Dividends received from equity investees	2,117	2,073	1,724
Changes in operating assets and liabilities:
Accounts Receivables	(30,165)	10,182	(18,734)
Other Assets	6,530	554	925
Accounts payable and accrued liabilities	(18,343)	957	(21,253)
Net cash (used in) provided by operating activities	(29,723)	1,662	(63,591)
Cash Flows from Investing Activities:
Purchases of property and equipment	(20,808)	(44,775)	(35,645)
Proceeds from disposition of property and equipment	20,674	55,321	10,655
Cash impact of sale of ERRV fleet		(5,140)
Purchase of subsidiary from joint venture	(8,445)		8,017
Investments in and advances to 50% or less owned companies	(2,206)	(17,395)	(43,386)
Return of investments and advances from 50% or less owned companies		461	16,263
Construction reserve funds transferred to short-term cash	3,745
Construction reserve funds utilized	9,148	15,168	17,300
Principal payments on notes due from equity investees	1,715
Net cash provided by (used in) investing activities	3,823	31,030	(26,796)
Cash Flows from Financing Activities:
Payments on long-term debt	(22,601)	(23,974)	(41,932)
Proceeds from issuance of long-term debt			53,546
Proceeds from exercise of stock options and warrants	2	1,424	833
Interest on Finance Leases	1
Issuance of stock			42,996
Issuance of warrants			12,809
Purchase of subsidiary shares from noncontrolling interests		(3,392)
Net cash (used in) provided by financing activities	(22,598)	(25,942)	68,252
Effects of Exchange Rate Changes on Cash, Cash Equivalents and Restricted Cash	30	(16,619)	299
Net Decrease in Cash, Cash Equivalents and Restricted Cash, Continuing Operations	(48,468)	(9,869)	(21,836)
Cash Flows from Discontinued Operations:
Operating Activities	8,217	13,778	10,566
Investing Activities	(8,318)	(15,388)	(4,353)
Financing Activities	941	0	998
Effects of Exchange Rate Changes on Cash, Restricted Cash and Cash Equivalents	119	1,674	(1,074)
Net Increase in Cash, Restricted Cash and Cash Equivalents on Discontinued Operations	959	64	6,137
Net Decrease in Cash, Cash Equivalents and Restricted Cash	(47,509)	(9,805)	(15,699)
Cash, Cash Equivalents and Restricted Cash, Beginning of Year	87,047	96,852	112,551
Cash, Cash Equivalents and Restricted Cash, End of Year	39,538	87,047	96,852
Supplemental disclosures:
Cash paid for interest, excluding capitalized interest	21,977	21,479	20,014
Income taxes refunded, net	1,094	1,999	321
Noncash Investing and Financing Activities:
Increase in property, plant and equipment related to an acquisition	142,282		140,257
Decrease in joint venture investments related to an acquisition	22,222
Increase in long-term debt related to an acquisition	75,569		$ 106,640
Increase in long-term debt related to asset purchases	21,252	10,626
Increase in capital expenditures in accounts payable and accrued liabilities	$ 3,193	2,409
ERRV Fleet Business
Cash Flows from Investing Activities:
Proceeds from disposition of property and equipment		$ 27,390

Nature of Operations and Accoun

Nature of Operations and Accounting Policies	12 Months Ended
	Dec. 31, 2020
Nature Of Operation And Accounting Policies [Abstract]
Nature of Operations and Accounting Policies	1. NATURE OF OPERATIONS AND ACCOUNTING POLICIES Nature of Operations and Segmentation. The consolidated financial statements include the accounts of SEACOR Marine and its consolidated subsidiaries (collectively referred to as the “Company”). The Company provides global marine and support transportation services to offshore oil, natural gas and windfarm facilities worldwide. The Company and its joint ventures operate a diverse fleet of offshore support and specialty vessels that (i) deliver cargo and personnel to offshore installations, (ii) handle anchors and mooring equipment required to tether rigs to the seabed, (iii) tow rigs and assist in placing them on location and moving them between regions, (iv) provide construction, well work-over and decommissioning support and (v) carry and launch equipment used underwater in drilling and well installation, maintenance, inspection and repair. Additionally, the Company’s vessels provide accommodations for technicians and specialists, safety support and emergency response services. The Company’s fleet also includes crew transfer vessels (“CTVs”) used primarily in windfarm operations. Accounting standards require public business enterprises to report information about each of their operating business segments that exceed certain quantitative thresholds or meet certain other reporting requirements. Operating business segments have been defined as a component of an enterprise about which separate financial information is available and is evaluated regularly by the chief operating decision maker in assessing performance. As a result of the announced sale of Windcat Workboats Holdings Ltd (“Windcat Workboats”), the Company’s indirect wholly owned subsidiary, and the CTV business of Windcat Workboats (the “Windcat Workboats CTV Business”) on December 18, 2020, the Company classified the CTV assets of the Windcat Workboats CTV Business as Assets held for sale as of December 31, 2020. Unless the context indicates otherwise, all of the results presented exclude the CTV operations of the Windcat Workboats CTV Business which are classified as Assets held for sale. The Company has identified the following five principal geographic regions as its reporting segments: United States, primarily Gulf of Mexico. As of December 31, 2020, 23 vessels were located in the U.S. Gulf of Mexico, including 17 owned, three leased-in, two joint-ventured and one managed-in. The Company’s vessels in this market support deep-water anchor handling, fast cargo transport, general cargo transport, well intervention, work-over, decommissioning and diving support operations. Africa, primarily West Africa. As of December 31, 2020, 15 vessels were located in West Africa, including 13 owned, one leased-in and one joint-ventured. The Company’s vessels in this area generally support projects for major oil companies, primarily in Angola and Nigeria. Middle East and Asia. As of December 31, 2020, 23 vessels were located in the Middle East and Asia, including 20 owned, two joint-ventured and one managed. The Company’s vessels in this area generally support exploration, personnel transport and seasonal construction activities in Egypt, Israel and Malaysia and countries along the Arabian Gulf and Arabian Sea, such as Saudi Arabia, the United Arab Emirates and Qatar. Latin America. As of December 31, 2020, 38 vessels were located in this region, including eight owned and 30 joint ventured. Of these joint-ventured vessels, (i) 16 are owned by Mantenimiento Express Maritimo, S.A.P.I. de C.V. (“MexMar”), a joint venture company that is 49% owned by SEACOR Marine International LLC (“SMI”), a wholly owned subsidiary of SEACOR Marine, and 51% owned by subsidiaries of Proyectos Globales de Energía y Servicios CME, S.A. de C.V. (“CME”), and (ii) 13 are owned by MEXMAR Offshore International LLC (“MEXMAR Offshore”), a joint venture company that is 49% owned by SMI and 51% owned by a subsidiary of CME. These vessels, consisting of a fleet of FSVs, supply, specialty and liftboat vessels, provide support for exploration and production activities in Mexico, Brazil and Guyana. From time to time, the Company’s vessels also work in Trinidad and Tobago, and Colombia. Europe, primarily North Sea. As of December 31, 2020, the Company had two owned vessels that are were classified in our continuing operations, located in this region, supporting the construction and maintenance of offshore wind turbines as well as supporting oil and gas explorations and production operations in the North Sea. On December 18, 2020, the Company announced the sale of its Windcat Workboats CTV Business (“Windcat Sale”), comprised of 46 CTVs located in Europe providing crew transfer to offshore wind platforms, which closed on January 12, 2021. As a result of the announced sale of the Windcat Workboats CTV Business on December 18, 2020, the Company classified the CTV assets of the Windcat Workboats CTV Business as Assets held for sale as of December 31, 2020 Basis of Consolidation. The consolidated financial statements include the accounts of SEACOR Marine and its controlled subsidiaries. Control is generally deemed to exist if the Company has greater than 50% of the voting rights of a subsidiary. All significant intercompany accounts and transactions are eliminated in the combination and consolidation. Noncontrolling interests in consolidated subsidiaries are included in the consolidated balance sheets as a separate component of equity. The Company reports consolidated net income (loss) inclusive of both the Company ’ s and the noncontrolling interests' share, as well as the amounts of consolidated net income (loss) attributable to each of the Company and the noncontrolling interests. If a subsidiary is deconsolidated upon a change in control, any retained noncontrolled equity investment in the former controlled subsidiary is measured at fair value and a gain or loss is recognized in net income (loss) based on such fair value. If a subsidiary is consolidated upon a change in control, any previous noncontrolled equity investment in the subsidiary is measured at fair value and a gain or loss is recognized in net income (loss) based on such fair value. The Company employs the equity method of accounting for investments in 50% or less owned companies that it does not control but has the ability to exercise significant influence over the operating and financial policies of the business venture. Significant influence is generally deemed to exist if the Company has between 20% and 50% of the voting rights of a business venture, but may exist when the Company’s ownership percentage is less than 20%. In certain circumstances, the Company may have an economic interest in excess of 50% but may not control and consolidate the business venture. Conversely, the Company may have an economic interest less than 50% but may control and consolidate the business venture. The Company reports its investments in and advances to these business ventures in the accompanying consolidated balance sheets as investments, at equity, and advances to 50% or less owned companies. The Company reports its share of earnings from investments in 50% or less owned companies in the accompanying consolidated statements of loss as equity in earnings (losses) of 50% or less owned companies, net of tax. The Company reports its qualifying investments at cost, less impairment if any, plus or minus observable price changes in orderly transactions for an identical or similar investment of the same issuer for its investments in 50% or less owned companies it does not control or exercise significant influence. These investments in private companies are adjusted for capital distributions and other-than-temporary declines in fair value. Certain reclassifications were made to previously reported amounts in the consolidated financial statements and notes thereto to make them consistent with the current period presentation. Use of Estimates. The preparation of financial statements in conformity with accounting principles generally accepted in the U.S. requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Such estimates include those related to deferred revenues, allowance for credit losses, useful lives of property and equipment, impairments, income tax provisions and certain accrued liabilities. Actual results could differ from estimates and those differences may be material. Revenue Recognition. The Company contracts with various customers to carry out management services for vessels as agents for and on behalf of ship owners. These services include crew management, technical management, commercial management, insurance arrangements, sale and purchase of vessels, provisions and bunkering. As the manager of the vessels, the Company undertakes to use its best endeavors to provide the agreed management services as agents for and on behalf of the owners in accordance with sound ship management practice and to protect and promote the interest of the owners in all matters relating to the provision of services hereunder. The Company also contracts with various customers to carry out management services regarding engineering for vessel construction and vessel conversions. The vast majority of the ship management agreements span over the length of one to three years and are typically billed on a monthly basis. The Company transfers control of the service to the customer and satisfies its performance obligation over the term of the contract, and therefore recognized revenue over the term of the contract while related costs are expensed as incurred. Revenue that does not meet these criteria is deferred until the criteria is met and such revenue is considered a contract liability. Contract liabilities, which are included in other current liabilities from continuing operations in the accompanying consolidated balance sheets, for the years ended December 31 were as follows (in thousands): 2020 2019 2018 Balance at beginning of year $ 4,755 $ 1,327 $ 10,104 Revenues deferred during the year 2,042 8,134 3,518 Revenues recognized during the year (3,490 ) (4,706 ) (12,295 ) Balance at end of year $ 3,307 $ 4,755 $ 1,327 As of December 31, 2020 the Company deferred revenues of $3.3 million primarily related to $2.0 million of prepaid vessel management fees, $0.8 million related to the time charter of offshore support vessels to customers from which collections were not reasonably assured and $0.5 million of prepaid charter modification and reservation fees. The Company earns revenue primarily from the time charter and bareboat charter of vessels to customers. Since the Company charges customers based upon daily rates of hire, vessel revenues are recognized on a daily basis throughout the contract period. Under a time charter, the Company provides a vessel to a customer and is responsible for all operating expenses, typically excluding fuel. Under a bareboat charter, the Company provides a vessel to a customer and the customer assumes responsibility for all operating expenses and assumes all risks of operation. In the U.S. Gulf of Mexico, time charter durations and rates are typically established in the context of master service agreements that govern the terms and conditions of the charter. From time to time, the Company may also participate in pooling arrangements. In a pooling arrangement, the time charter revenues of certain of the Company’s vessels are shared with the time charter revenues of certain vessels of similar type owned by non-affiliated vessel owners based upon an agreed formula. On January 9, 2019, the only active pooling arrangement was terminated, and three FSV’s were purchased by the Company. Contract or charter durations may range from several days to several years. Charters vary in length from short-term to multi-year periods, many with cancellation clauses and without early termination penalties. As a result of options and frequent renewals, the stated duration of charters may have little correlation with the length of time the vessel is contracted to provide services to a particular customer. Cash Equivalents. The Company considers all highly liquid investments with an original maturity of three months or less, when purchased, to be cash equivalents. Cash equivalents consist of U.S. treasury securities, money market instruments, time deposits and overnight investments. Restricted Cash. Restricted cash primarily relates to banking facility requirements. For the year ended December 31, cash, cash equivalents and restricted cash from continuing operations consists of: 2020 2019 Cash $ 32,666 $ 81,382 Restricted cash 3,352 3,104 Total $ 36,018 $ 84,486 Trade and Other Receivables. Customers are primarily major integrated national and international oil companies, large independent oil and natural gas exploration and production companies, and offshore windfarm operations. Customers are granted credit on a short-term basis and the related credit risks are minimal. Other receivables consist primarily of operating expenses the Company incurs in relation to vessels it manages for other entities, as well as insurance and income tax receivables. The Company routinely reviews its receivables and makes provisions for credit losses; however, those provisions are estimates and actual results may materially differ from those estimates. Trade receivables are deemed uncollectible and are removed from accounts receivable and the allowance for credit losses when collection efforts have been exhausted. Derivative Instruments. The Company accounts for derivatives through the use of a fair value concept whereby all of the Company’s derivative positions are stated at fair value in the accompanying consolidated balance sheets. Realized and unrealized gains and losses on derivatives not designated as hedges are reported in the accompanying consolidated statements of loss as Derivative gains (losses), net. Realized and unrealized gains and losses on derivatives designated as fair value hedges are recognized as corresponding increases or decreases in the fair value of the underlying hedged item to the extent they are effective, with any ineffective portion reported in the accompanying consolidated statements of loss as Derivative gains (losses), net. Realized and unrealized gains and losses on derivatives designated as cash flow hedges are reported as a component of other comprehensive loss in the accompanying consolidated statements of comprehensive loss to the extent they are effective and reclassified into earnings on the same line item associated with the hedged transaction and in the same period the hedged transaction affects earnings. Any ineffective portions of cash flow hedges are reported in the accompanying consolidated statements of loss as Derivative gains (losses), net. Realized and unrealized gains and losses on derivatives designated as cash flow hedges that are entered into by the Company’s 50% or less owned companies are also reported as a component of the Company’s other comprehensive loss in proportion to the Company’s ownership percentage, with reclassifications and ineffective portions being included in Equity in earnings (losses) of 50% or less owned companies, net of tax, in the accompanying consolidated statements of loss. Concentrations of Credit Risk. The Company is exposed to concentrations of credit risk associated with its cash and cash equivalents, restricted cash, construction reserve funds and derivative instruments. The Company minimizes its credit risk relating to these positions by monitoring the financial condition of the financial institutions and counterparties involved and by primarily conducting business with large, well-established financial institutions and diversifying its counterparties. The Company does not currently anticipate nonperformance by any of its significant counterparties. The Company is also exposed to concentrations of credit risk relating to its receivables due from customers described above. The Company does not generally require collateral or other security to support its outstanding receivables. The Company minimizes its credit risk relating to receivables by performing ongoing credit evaluations and, to date, credit losses have not been material. Inventories. Inventories, which consist of fuel and supplies, are stated at the lower of cost (using the first-in, first-out method) or market. The Company records write-downs, as needed, to adjust the carrying amount of inventories to the lower of cost or market. In the year ended December 31 , 2020, 201 9 and 201 8 , t here were no inventory reserves . Property and Equipment. Equipment, stated at cost, is depreciated using the straight-line method over the estimated useful life of the asset to an estimated salvage value. With respect to offshore support vessels, the estimated useful life is typically based upon a newly built vessel being placed into service and represents the point at which it is typically not justifiable for the Company to continue to operate the vessel in the same or similar manner. From time to time, the Company may acquire older vessels that have already exceeded the Company’s useful life policy, in which case the Company depreciates such vessels based on its best estimate of remaining useful life, typically the next regulatory survey or certification date. As of December 31, 2020, the estimated useful life (in years) of each of the Company’s major categories of new offshore support vessels was as follows: Offshore Support Vessels: CTVs 10 All other offshore support vessels (excluding crew transfer) 20 The Company’s property and equipment from continuing operations as of December 31 was as follows (in thousands): Historical Cost (1) Accumulated Depreciation Net Book Value 2020 Offshore support vessels: AHTS ( 2) $ 50,189 $ (31,779 ) $ 18,410 FSV ( 3) 375,747 (104,739 ) 271,008 Supply 238,624 (15,991 ) 222,633 Liftboats 321,751 (117,364 ) 204,387 Crew transfer 3,163 (3,138 ) 25 General machinery and spares 7,746 (7,733 ) 13 Other (4) 15,653 (10,794 ) 4,859 $ 1,012,873 $ (291,538 ) $ 721,335 2019 Offshore support vessels: AHTS ( 2) $ 94,078 $ (73,095 ) $ 20,983 FSV ( 3) 388,460 (101,295 ) 287,165 Supply 44,958 (8,471 ) 36,487 Specialty 14,805 (10,466 ) 4,339 Liftboats 327,028 (93,166 ) 233,862 Crew transfer 5,032 (4,518 ) 514 General machinery and spares 7,650 (7,648 ) 2 Other (4) 17,013 (10,258 ) 6,755 $ 899,024 $ (308,917 ) $ 590,107 (1) Includes property and equipment acquired in business acquisitions at acquisition date fair value, and net of the impact of recognized impairment charges. (2) Anchor Handling Towing (“AHTS”). (3) Fast support vessels (“FSVs”). ( 4 ) Includes land, buildings, leasehold improvements, vehicles and other property and equipment. Depreciation and amortization expense from continuing operations totaled $57.2 million, $57.2 million and $61.4 million in 2020, 2019 and 2018, respectively. Depreciation and amortization from discontinued operations totaled $6.2 million, $ million and $ million in 2020, 2019 and 2018. On December 2, 2019, the Company completed the sale of its North Sea standby business, comprised of 18 emergency response and rescue vehicles (“ERRVs”) with a net book value of $24.3 million. Depreciation and amortization expense totaled $3.5 million and $3.4 million in 2019 and 2018, respectively. Equipment maintenance and repair costs and the costs of routine overhauls, drydockings and inspections performed on vessels and equipment are charged to operating expense as incurred. Expenditures that extend the useful life or improve the marketing and commercial characteristics of vessels, as well as major renewals and improvements to other properties, are capitalized. Certain interest costs incurred during the construction of vessels are capitalized as part of the vessels’ carrying values and are amortized over such vessels estimated useful lives. Capitalized interest totaled $0.7 million, $1.5 million and $2.4 million in 2020, 2019 and 2018, respectively. Impairment of Long-Lived Assets. The Company performs an impairment analysis of long-lived assets used in operations, including intangible assets, when indicators of impairment are present. These indicators may include a significant decrease in the market price of a long-lived asset or asset group, a significant adverse change in the extent or manner in which a long-lived asset or asset group is being used or in its physical condition, or a current period operating or cash flow loss combined with a history of operating or cash flow losses or a forecast that demonstrates continuing losses associated with the use of a long-lived asset or asset group. If the carrying values of the assets are not recoverable, as determined by their estimated future undiscounted cash flows, the estimated fair value of the assets or asset groups are compared to their current carrying values and impairment charges are recorded if the carrying value exceeds fair value. As a result of the difficult conditions experienced in the offshore oil and natural gas markets beginning in the second half of 2014 and the corresponding reductions in utilization and rates per day worked of its fleet, the Company identified indicators of impairment and recognized impairment charges primarily associated with its AHTS fleet, its liftboat fleet, certain specialty vessels, vessels removed from service and goodwill. When reviewing its fleet for impairment, the Company groups vessels with similar operating and marketing characteristics, including cold-stacked vessels expected to return to active service, into vessel classes. All other vessels, including vessels retired and removed from service, are evaluated for impairment on a vessel by vessel basis. During the year ended December 31, 2020, the Company recorded non-cash impairment charges totaling million. The Company recorded partial impairments ($5.3 million) on the five-company owned liftboat vessels based on outside valuations of its remaining fleet. Estimated fair values for the Company owned vessels were established by independent appraisers based on researched market information, replacement cost information and other data. If market conditions further decline from the depressed utilization and rates per day worked experienced over the last three years, fair values based on future appraisals could decline significantly. In addition, the Company impaired ($7.0 million) on two leased-in liftboat vessels that based on current market environment, were determined that neither of these two leased-in vessels would return to active service during their remaining lease terms. Additionally, one leased-in anchor-handling towing supply (“AHTS”) was impaired ($0.5 million), one specialty vessel was impaired ($1.2 million) and one hull that was included in construction in progress was impaired ($4.8 million). During the year ended December 31, 2019, the Company recorded non-cash impairment charges of $12.0 million, primarily related to four AHTS vessels previously removed from service and adjusted to scrap value, and four fast support vessels (“FSV”), each of which has been adjusted to indicative sales price, and two leased-in vessels (one AHTS and one platform supply vessel “PSV”), adjusted for indicative future cash flows . During the year ended December 31, 2018, the Company recorded non-cash impairment charges of $14.6 million primarily associated with its AHTS fleet (four owned vessels and three leased-in vessels) and one specialty vessel. The Company’s other vessel classes and other individual vessels in active service and cold-stacked status, for which no impairment was deemed necessary, have generally experienced a less severe decline in utilization and rates per day worked based on specific market factors. The market factors include vessels with more general utility to a broad range of customers (e.g., FSVs), vessels required for customers to meet regulatory mandates and operating under multiple year contracts or vessels that service customers outside of the offshore oil and natural gas market (e.g., CTVs). For vessel classes and individual vessels with indicators of impairment but not recently impaired as of December 31, 2020 the Company has estimated that their future undiscounted cash flows exceed their current carrying values. The Company’s estimates of future undiscounted cash flows are highly subjective as utilization and rates per day worked are uncertain, including the timing of an estimated market recovery in the offshore oil and natural gas markets and the timing and cost of reactivating cold-stacked vessels. If market conditions decline further, changes in the Company’s expectations on future cash flows may result in recognizing additional impairment charges related to its long-lived assets in future periods. Impairment of 50% or Less Owned Companies. Investments in 50% or less owned companies are reviewed periodically to assess whether there is an other-than-temporary decline in the carrying value of the investment. In its evaluation, the Company considers, among other items, recent and expected financial performance and returns, impairments recorded by the investee and the capital structure of the investee. When the Company determines the estimated fair value of an investment is below carrying value and the decline is other-than-temporary, the investment is written down to its estimated fair value. Actual results may vary from the Company’s estimates due to the uncertainty regarding projected financial performance, the severity and expected duration of declines in value, and the available liquidity in the capital markets to support the continuing operations of the investee, among other factors. Although the Company believes its assumptions and estimates are reasonable, the investee’s actual performance compared with the estimates could produce different results and lead to additional impairment charges in future periods. No impairment charges of investments in 50% or less owned companies were incurred for the years ended December 31, 2020 and 2019. During the year ended December 31, 2018 the Company recognized impairment charges of $1.2 million net of tax, related to its 50% or less owned companies (see “Note 5. Investments, at Equity, and Advances to 50% or Less Owned Companies”). Business Combinations. The Company recognizes 100% of the fair value of assets acquired, liabilities assumed, and noncontrolling interests when the acquisition constitutes a change in control of the acquired entity. Shares issued in consideration for a business combination, contingent consideration arrangements and pre-acquisition loss and gain contingencies are all measured and recorded at their acquisition-date fair value. Subsequent changes to fair value of contingent consideration arrangements are generally reflected in earnings. Acquisition-related transaction costs are expensed as incurred and any changes in an acquirer’s existing income tax valuation allowances and tax uncertainty accruals are recorded as an adjustment to income tax expense. The operating results of entities acquired are included in the accompanying consolidated statements of loss from the date of acquisition (see “Note 3 Business Acquisitions”). Debt Discount and Issue Costs . Debt discounts and costs incurred in connection with the issuance of debt are amortized over the life of the related debt using the effective interest rate method for term loans and straight-line method for revolving credit facilities and are included in interest expense in the accompanying consolidated statements of loss. Self-insurance Liabilities . The Company maintains marine hull, liability and war risk, general liability, workers compensation and other insurance customary in the industry in which it operates. Both the marine hull and liability policies have annual aggregate deductibles. Marine hull annual aggregate deductibles are accrued as claims are incurred while marine liability annual aggregate deductibles are accrued based on historical loss experience. Exposure to the health benefit plans are limited by maintaining stop-loss and aggregate liability coverage. To the extent that estimated self-insurance losses, including the accrual of annual aggregate deductibles, differ from actual losses realized, the Company’s insurance reserves could differ significantly and may result in either higher or lower insurance expense in future periods. Income Taxes . Deferred income tax assets and liabilities have been provided in recognition of the income tax effect attributable to the book and tax basis differences of assets and liabilities reported in the accompanying consolidated financial statements. Deferred tax assets or liabilities are provided using the enacted tax rates expected to apply to taxable income in the periods in which they are expected to be settled or realized. Interest and penalties relating to uncertain tax positions are recognized in interest expense and administrative and general, respectively, in the accompanying consolidated statements of loss. The Company records a valuation allowance to reduce its deferred tax assets if it is more likely than not that some portion or all of the deferred tax assets will not be realized. The Global Intangible Low Taxed Income (“GILTI”) regime effectively imposes a minimum tax on worldwide foreign earnings and subjects U.S. shareholders of controlled foreign corporations (“CFCs”) to current taxation on certain income earned through a CFC. The Company has made the policy election to record any liability, associated with GILTI in the period in which it is incurred. SEACOR Marine was included in the consolidated U.S. federal income tax return of SEACOR Holdings Inc. (“SEACOR Holdings”) through 2016. SEACOR Holdings’ policy for allocation of U.S. federal income taxes required its domestic subsidiaries included in the consolidated U.S. federal income tax return to compute their provision for U.S. federal income taxes on a separate company basis and settle with SEACOR Holdings. In the normal course of business, the Company or SEACOR Holdings may be subject to challenges from tax authorities regarding the amount of taxes due for the Company. These challenges may alter the timing or amount of taxable income or deductions. As part of the calculation of income tax expense, the Company determines whether the benefits of its tax positions are at least more likely than not of being sustained based on the technical merits of the tax position. For tax positions that are more likely than not of being sustained, the Company accrues the largest amount of the tax benefit that is more likely than not of being sustained. Such accruals require management to make estimates and judgments with respect to the ultimate outcome of its tax benefits and actual results could vary materially from these estimates. On June 26, 2020, the Company entered into the Tax Refund Agreement with SEACOR Holdings (see “Note 17. Related Party Transactions”). Deferred Gains - Vessel Sale-Leaseback Transactions and Financed Vessel Sales . Prior to the implementation of ASC 842, the Company entered into vessel sale-leaseback transactions with finance companies or provided seller financing on sales of its vessels to third-parties or to 50% or less owned companies. A portion of the gains realized from these transactions was not immediately recognized in income but rather was recorded in the accompanying consolidated balance sheets in deferred gains and other liabilities. In sale-leaseback transactions, gains were deferred to the extent of the present value of future minimum lease payments and were amortized as reductions to rental expense over the applicable lease terms (see “Note 7. Leases”). When the Company determines that future cash inflows do not support future lease cash obligations, the Company records an impairment expense for the amount of the cash flow shortage of all future lease costs, costs to maintain the vessel to the end of the lease term, and costs to return the vessel to its owner, less the amount of any unamortized deferred gains. In financed vessel sales, gains were deferred to the extent that the repayment of purchase notes were dependent on the future operations of the sold vessels and were amortized based on cash received from the buyers. Unamortized deferred gains for four vessels under sale-leaseback agreements were fully recognized in 2019 as an

Transformation, Facility Restru

Transformation, Facility Restructuring and Severance Charges	12 Months Ended
	Dec. 31, 2020
Restructuring And Related Activities [Abstract]
Transformation, Facility Restructuring and Severance Charges	2. TRANSFORMATION, FACILITY RESTRUCTURING AND SEVERANCE CHARGES Due to the highly competitive nature of the Company’s business and the continuing losses incurred over the last few years, the Company reduced its overall cost structure and workforce to better align the Company with current activity levels. The transformation plan, which began in the third quarter of 2019 and extended through the third quarter of 2020 (the “Transformation Plan”), included a workforce reduction, organization restructuring, facility consolidations and other cost reduction measures and efficiency initiatives across the Company’s geographic regions. These initiatives impacted all of the Company’s reportable segments and are expected to result in annualized recurring savings of at least $8.0 million. In connection with the Transformation Plan, for the twelve months ended December 31, 2020, the Company recognized year-to-date restructuring and transformation charges of $1.2 million, The components of restructuring charges for the years ended December 31, 2020 and 2019, were as follows (in thousands): December 31, 2020 United States (primarily Gulf of Mexico) Africa (primarily West Africa) Middle East and Asia Latin America Europe (primarily North Sea) Total Transformation Plan Severance Charges $ 275 $ — $ 665 $ — $ 185 $ 1,125 Other Charges 31 — 31 — — 62 Total Charges $ 306 — $ 696 — $ 185 $ 1,187 December 31, 2019 United States (primarily Gulf of Mexico) Africa (primarily West Africa) Middle East and Asia Latin America Europe (primarily North Sea) Total Transformation Plan Severance Charges $ 2,995 $ — $ 184 $ — $ 200 $ 3,379 Other Charges 307 — 31 — — 339 Total Charges $ 3,302 — $ 215 — $ 200 $ 3,718 The severance and other restructuring charges gave rise to certain liabilities primarily related to liabilities accrued as part of the Transformation Plan. As of December 31, 2020, all related liabilities associated with the Transformation Plan have been recognized. The Transformation Plan was completed during the third quarter of 2020. No material future costs related to these efforts are expected, but to the extent the Company identifies additional opportunities for further costs reductions beyond the Transformation Plan, these opportunities may give rise to restructuring charges. On a cumulative basis, the Company recognized $4.9 million in restructuring charges.

Seacosco Acquisition

Seacosco Acquisition	12 Months Ended
	Dec. 31, 2020
Business Combinations [Abstract]
Business Acquisitions	3. BUSINESS ACQUISITIONS On May 31, 2020, SEACOR Offshore Asia LLC (“SEACOR Offshore Asia”), an indirect wholly-owned subsidiary of SEACOR Marine, entered into a Sale and Purchase Agreement (“SEACOSCO SPA”) with China Shipping Fan Tai Limited, a company incorporated under the laws of the British Virgin Islands, and China Shipping Industry (Hong Kong) Co., Limited, a company incorporated under the laws of the Hong Kong Special Administrative Region (together, the “SEACOSCO Sellers”), pursuant to which SEACOR Offshore Asia agreed to acquire the 50% membership interest in SEACOSCO Offshore LLC (such remaining interest, the “SEACOSCO Interests”) held by the SEACOSCO Sellers that the Company did not already own. On June 30, 2020, SEACOR Offshore Asia completed the acquisition of the SEACOSCO Interests from the SEACOSCO Sellers (the “SEACOSCO Acquisition”). As a result of the completion of the acquisition, the Company owns 100% of the membership interests in SEACOSCO Offshore LLC. On July 14, 2020, the name of SEACOSCO Offshore LLC was changed to SEACOR Offshore Delta LLC (“SEACOR Offshore Delta”). The price payable by SEACOR Offshore Asia for the membership interests was $28.2 million (the “SEACOSCO Purchase Price”), $8.4 million of which was paid to the Sellers at the closing of the transaction, with annual installment payments of $1.0 million, $2.5 million and $2.5 million payable in the first, second and third year after the signing date (the “SEACOSCO SPA Signing Date”), respectively, and the remaining $13.7 million due four years after such signing date. The deferred portion of the SEACOSCO Purchase Price accrues interest at a fixed rate of 1.5 %, 7.0 %, 7.5 % and 8.0 % for the first through fourth years after the SEACOSCO SPA Signing Date, respectively. SEACOR Offshore Delta is the owner of eight PSVs built by COSCO Shipping Heavy Industry (Guangdong) Co., Ltd. (the “COSCO (Guangdong) Shipyard” and such PSVs, the “SEACOR Delta PSVs”). The SEACOSCO Sellers obtained a second lien mortgage on the SEACOR Delta PSVs to secure the payment of the deferred portion of the SEACOSCO Purchase Price, and SEACOR Marine provided a limited deficiency guarantee solely with respect to the short-fall in vessel collateral value, if any, in the event the SEACOSCO Sellers exercise their remedies under the mortgages. The SEACOR Delta PSVs were initially acquired by vessel owning subsidiaries (“SEACOR Delta SPVs”) of SEACOR Offshore Delta pursuant to existing deferred purchase agreements with the COSCO (Guangdong) Shipyard (“Guangdong DPAs”) under which an aggregate of approximately $100.8 million was outstanding as of June 30, 2020 (the “SEACOR Delta Shipyard Financing”). As of December 31, 2020, $95.3 million was outstanding. The Guangdong DPAs provide for amortization of the purchase price for each vessel over a period of 10 years from delivery bearing floating interest rate of three-month LIBOR plus 4.0%. SEACOR Offshore Delta has taken delivery of all eight SEACOR Delta PSVs, seven with a 2018 or 2019 year of build, and one with a 2020 year of build. The payment obligations of the SEACOR Delta SPVs under the Guangdong DPAs for each vessel is secured by a first lien mortgage on the vessel and a pledge of the SEACOR Delta SPV’s equity, and SEACOR Marine provided a limited deficiency guarantee solely with respect to the short-fall in vessel collateral value, if any, in the event the COSCO (Guangdong) Shipyard exercises its remedies under the mortgages. Purchase Price Allocation. The eight SEACOR Delta PSVs are all based on plans from the same designer, have a similar age of construction (2018-2020) and were constructed at the same shipyard. Two of the vessels are high specification diesel/electric powered PSVs. The other six vessels are all “sister” vessels with identical specifications. These six vessels are high specification diesel/electric/hybrid powered vessels. In accordance with ASU No. 2017-01-Business Combinations (Topic 805): Clarifying the Definition of a Business, due to the fact that the assets acquired have substantially all of their fair value concentrated as a group of similar assets, this acquisition qualified as an asset purchase. The allocation of the purchase price for the Company’s acquired assets for the six months ended June 30 was as follows (in thousands): Assets Acquired (In Thousands): June 30, 2020 Current Assets 7,700 Fixed Assets 142,282 Current Liabilities (23,929 ) Book Value of Debt Acquired (100,759 ) Discount on Debt Acquired 25,190 Fair Value of Debt Acquired (75,569 ) Total Cost Basis for Purchase 50,484 Purchase Price $ (28,150 ) Acquisition costs (112 ) Equity Investment In SEACOR Offshore Delta (f/k/a SEACOSCO) (22,222 ) (50,484 )

Equipment Acquisitions and Disp

Equipment Acquisitions and Dispositions	12 Months Ended
	Dec. 31, 2020
Property Plant And Equipment [Abstract]
Equipment Acquisitions and Dispositions	4. EQUIPMENT ACQUISITIONS AND DISPOSITIONS Equipment Additions. The Company’s capital expenditures and payments on equipment were $20.8 million, $44.8 million, and $35.6 million in 2020, 2019 and 2018, respectively. Deliveries of offshore support vessels for the years ended December 31 were as follows: 2020 (1) 2019 (2) 2018 (3) FSV — 2 6 Supply 4 2 5 Liftboat — — — 4 4 11 (1) Excludes three CTVs as assets held for sale and seven PSVs acquired as part of the SEACOSCO Acquisition (See “Note 3. Business Acquisitions”). (2) Ex cludes two CTVs as assets held for sale. ( 3 ) Ex Equipment Dispositions. On January 12, 2021, a wholly-owned subsidiary of SEACOR Marine Holdings Inc. (the “Company”), completed the sale of the Company’s Windcat Workboats CTV business through the sale of 100% of the equity of Windcat Workboats, a wholly-owned subsidiary of the Company (“Windcat” and together with its subsidiaries, the “Windcat Group”), to CMB N.V. (the “Windcat Buyer”) pursuant to a Sale and Purchase Agreement entered into on December 18, 2020. At closing, the Windcat Buyer paid to the Company an aggregate purchase price of £32.8 million. After deducting transaction costs and expenses and giving effect to foreign exchange rate hedges, the Company received net cash proceeds of approximately US$42.6 million. The Windcat Buyer also assumed all of the approximately £20.4 million of debt outstanding under Windcat Workboat’s existing revolving credit facility. As of December 31, 2020, the Windcat Group owned a total of 41 CTVs and held interests in an additional five CTVs through its joint ventures, all of which were included in the sale. These vessels have been classified as and included as Assets held for sale as of December 31, 2020. The Company recognized a gain on the sale of Windcat Workboats in January 2021 of approximately $22.8 million. During the year ended December 31, 2020, the Company sold two anchor handling towing supply (“AHTS”) vessels and one specialty vessel previously removed from service, four FSVs, one specialty vessels, one vessel under construction and other equipment for $21.6 million ($20.7 million cash and $0.9 million in previously received deposits) and gains of $1.2 million. For the year ended December 31, 2019, the Company completed the sale of its ERRV fleet business, which consisted of 18 vessels with a net book value of $23.4 million. The net proceeds from the sale of the ERRV fleet, including property and equipment, were approximately $27.4 million resulting in a net loss on dispositions of $9.1 million. Additional consideration of up to £4 million (equivalent to approximately $5.2 million based on the exchange rate at the time of the sale) may be payable to the Company based on revenue targets being achieved in 2021. The revenue targets were not achieved in 2020 and as such no additional consideration payments were made. In addition to the sale of the North Sea ERRV fleet, for the year ended December 31, 2019, the Company sold one AHTS vessels, five During the year ended December 31, 2018, the Company sold property and equipment for net proceeds of $12.3 million ($12.2 million in cash and $0.1 million in cash deposits previously received) and recorded gains of $5.7 million, all of which were recognized at the time of sale. Major equipment dispositions for the years ended December 31 were as follows: 2020 (1) 2019 2018 ( 2 ) AHTS 2 1 1 FSV 4 5 9 Supply 1 5 — CTV — — — Liftboats 1 3 2 Specialty 2 — — 10 14 12 (1) Excludes three (2) Excludes one CTV from assets held for sale.

Investments, at Equity, and Adv

Investments, at Equity, and Advances to 50% or Less Owned Companies	12 Months Ended
	Dec. 31, 2020
Schedule Of Investments [Abstract]
Investments, at Equity, and Advances to 50% or Less Owned Companies	5. Investments, at equity, and advances to 50% or less owned companies as of December 31 were as follows (in thousands): Ownership 2020 2019 MexMar 49.0 % $ 50,037 $ 54,249 SEACOSCO ( 1) 50.0 % — 37,480 OSV Partners ( 2) 30.4 % 9,094 10,668 SEACOR Marlin 49.0 % 7,979 7,929 MEXMAR Offshore ( 3) 49.0 % 1,960 — Offshore Vessel Holdings 49.0 % 2,388 7,905 Other 20.0% — 50.0% 3,850 2,600 $ 75,308 $ 120,831 (1) The Company acquired the remaining 50% of the SEACOSCO Joint Venture that it did not own on June 30, 2020. (2) The Company owns 66.7 % of the General Partner and 29.7 % of the limited Partner . (3) This Joint Venture holds the investment in UP Offshore . Combined Condensed Financial Information of Other Investees. Summarized financial information of the Company’s other investees, at equity, as of and for the years ended December 31 was as follows (in thousands): 2020 2019 Current assets $ 109,687 $ 106,051 Noncurrent assets 259,424 607,541 Current liabilities 109,074 104,423 Noncurrent liabilities 115,626 331,357 2020 2019 2018 Operating Revenues $ 160,781 $ 136,690 $ 105,163 Costs and Expenses: Operating and administrative 142,228 116,517 75,529 Depreciation 27,044 27,412 25,359 169,272 143,929 100,888 Loss on Asset Dispositions and Impairments, Net — (166 ) (262 ) Operating (Loss) Income $ (8,491 ) $ (7,405 ) $ 4,013 Net Loss $ (18,229 ) $ (36,816 ) $ (14,861 ) As of December 31, 2020 and 2019, cumulative undistributed net earnings of all 50% or less owned companies included in the Company’s consolidated retained earnings were $20.7 million and $14.7 million, respectively. MexMar. MexMar owns and operates 16 offshore support vessels in Mexico and manages four PSV’s and one FSV on behalf of OVH in Mexico. During the years ended December 31, 2020 and 2019, there were no returns of capital advances or distributions to shareholders. During the year ended December 31, 2018, MexMar returned previously provided capital advances of $9.8 million. During the years ended December 31, 2020, 2019 and 2018 the Company charged $0.3 million of vessel management fees to MexMar. SEACOSCO. On May 31, 2020, SEACOR Offshore Asia, entered into the SEACOSCO SPA, pursuant to which SEACOR Offshore Asia agreed to acquire the SEACOSCO Interests held by the SEACOSCO Sellers that the Company did not already own. On June 30, 2020, SEACOR Offshore Asia completed the SEACOSCO Acquisition OSV Partners. SEACOR OSV Partners GP LLC and SEACOR OSV Partners I LP (collectively “OSV Partners”) own and operate five offshore support vessels. On September 28, 2018, OSV Partners amended its term loan facility to, among other things, extend its maturity to September 28, 2021, and in connection therewith, the Company participated in a $5.0 million preferred equity offering by OSV Partners and subordinated loan in the amount of $5.0 million issued by OSV Partners, investing $1.1 million in such preferred equity (and committing to invest an additional $1.1 million in such preferred equity if called by the general partner of OSV Partners prior to September 30, 2020) and providing $2.1 million of such loan. On December 18, 2019, the general partner of OSV Partners called the remaining commitments of the Company and other limited partners and the Company satisfied its commitment with an additional $1.1 million investment in such preferred equity. The Company has no further commitments to OSV Partners. On December 23, 2019, OSV Partners further amended its term loan facility to, among other things, provide for interest-only payments during 2020 with the next principal payment due March 31, 2021. The lenders to OSV Partners have no recourse to the Company for outstanding amounts under the facility, and the Company is not obligated to participate in any future investment in or loan any money to OSV Partners. For the years ended December 31, 2020 and 2019, vessel management fees were abated and not charged. For the year ended December 31, 2018, the Company received $0.6 million, of vessel management fees from OSV Partners. SEACOR Marlin. SEACOR Marlin LLC (“SEACOR Marlin”) own and operate Seacor Marlin supply vessel. On September 13, 2018, the Company sold 51% of SEACOR Marlin to MEXMAR Offshore (MI) LLC, a wholly owned subsidiary of MexMar, for $8.0 million in cash, which generated a gain of $0.4 million. The Seacor Marlin supply vessel was pledged as collateral under the MexMar credit facility, for which the Company receives an annual collateral fee. MEXMAR Offshore. On December 20, 2018, UP Offshore (Bahamas) Ltds (“UP Offshore”), a provider of offshore support vessel services to the energy industry in Brazil, was acquired by MEXMAR Offshore, a new joint venture company that is 49% owned by the Company, and 51% owned by a subsidiary of CME. MEXMAR Offshore acquired UP Offshore for nominal consideration, re-financed its existing debt to fund capital expenditures on two vessels and a $10.0 million loan to fund new working capital requirements. During the year ended December 31, 2019, UP Offshore sold one PSV to a third party and repositioned three PSV’s to Mexico. Offshore Vessel Holdings (“OVH”). On December 28, 2018, the Company invested $4.9 million for a 49% interest in OVH, the remaining 51% is owned by a subsidiary of CME. OVH invests in offshore assets and charters marine equipment. During the year ended December 31, 2019 OVH loaned $10.0 million to Operadora Productura Mexsicana, a drilling company in Mexico which owns and operates two jackup drilling rigs (“OPM”), chartered in three PSV’s from UP Offshore and purchased one FSV from the Company for $2.4 million through a seller’s finance agreement. Other. The Company’s other 50% or less owned companies own and operate no vessels. During the year ended December 31, 2020, the Company received dividends of $2.1 million from these 50% or less owned companies. During the year ended December 31, 2019, the Company received dividends of $2.1 million and $0.5 million of return capital from these 50% or less owned companies. During the year ended December 31, 2018, the Company recognized impairment charges of $1.2 million, net of tax, to reduce its investment carrying value in a certain 50% or less owned company to zero. During the year ended December 31, 2020, no vessel management fees were received from these 50% or less owned companies. In the years ended December 31, 2019 and 2018, the Company received less than $0.1 million and $0.3 million, respectively.

Construction Reserve Funds

Construction Reserve Funds	12 Months Ended
	Dec. 31, 2020
Restricted Cash And Investments [Abstract]
Construction Reserve Funds	6. The Company has established, pursuant to Section 511 of the Merchant Marine Act, 1936, as amended, construction reserve fund accounts subject to agreements with the Maritime Administration (“MARAD”). In accordance with this statute, the Company is permitted to deposit proceeds from the sale of certain vessels into the construction reserve fund accounts and defer the taxable gains realized from the sale of those vessels. Qualified withdrawals from the construction reserve fund accounts are only permitted for the purpose of acquiring qualified U.S.-flag vessels as defined in the statute and approved by MARAD. To the extent that sales proceeds are reinvested in replacement vessels, the carryover depreciable tax basis of the vessels originally sold is attributed to the U.S.-flag vessels acquired using such qualified withdrawals. The construction reserve funds must be committed for expenditure within three years of the date of sale of the equipment, subject to two one-year As of December 31, 2020, the Company had $4.2 million in short-term construction reserve funds included in cash and cash equivalents.

Leases

Leases	12 Months Ended
	Dec. 31, 2020
Leases [Abstract]
Leases	7. LEASES On February 25, 2016, the FASB issued a comprehensive new leasing standard, ASC 842, Leases, As of December 31, 2020, the Company leases two AHTS vessels, one liftboat, one FSV and certain facilities and other equipment. The leases typically contain purchase and renewal options or rights of first refusal with respect to the sale or lease of the equipment. As of December 31, 2020, the remaining lease terms of the vessels have remaining durations from eight to 12 months. The lease terms of the other equipment range in duration from 11 to 312 months. As of December 31, 2020, future minimum payments for leases for the years ended December 31 were as follows (in thousands): Operating Leases Finance Leases 2021 $ 7,855 $ 42 2022 639 39 2023 628 39 2024 559 36 2025 539 — Years subsequent to 2025 4,215 — 14,435 156 Interest component (3,060 ) (15 ) 11,375 141 Current portion of long-term operating lease liabilities (7,030 ) (36 ) Long-term operating lease liabilities $ 4,345 $ 105 For the years ended December 31, the components of lease expense were as follows (in thousands): 2020 2019 Operating lease expense (1) $ 6,205 $ 13,442 Finance lease cost: Amortization of finance lease asset (1) 11 — Interest on lease liabilities (2) 1 — Short-term lease costs (1) 1,320 2,398 $ 7,537 $ 15,840 (1) Included in selling, general and administrative expenses and amortization costs in the consolidated statements of loss. (2) Included in interest expense in the consolidated statements of loss. For the year ended December 31, 2020, supplemental cashflow information related to leases were as follows (in thousands): 2020 Operating cash flows from operating leases $ 14,785 Right-of-use assets obtained for operating lease liabilities 1,706 Right-of-use assets obtained for finance lease liabilities 140 For the year ended December 31, 2020, other information related to leases were as follows: 2020 Weighted average remaining lease term, in years - operating leases 7.6 Weighted average remaining lease term, in years - finance leases 4.2 Weighted average discount rate - operating leases 4.7 % Weighted average discount - finance leases 5.3 % The Company performed an impairment analysis and determined that some of the leased offshore support vessels are impaired due to an operating or cash flow loss currently and in the forecasted future. The Company recorded impairment losses of $5.9 million for two such leases for the year ended December 31, 2020 and $5.3 million for one such lease for the year ended December 31, 2019.

Long Term Debt

Long Term Debt	12 Months Ended
	Dec. 31, 2020
Debt Disclosure [Abstract]
Long Term Debt	8. The Company’s long-term debt obligations as of December 31 were as follows (in thousands): December 31,2020 December 31, 2019 Recourse Long-term debt ( 1) Convertible Senior Notes $ 125,000 $ 125,000 SEACOR Marine Foreign Holdings Credit Facility 100,750 113,750 Sea-Cat Crewzer III Term Loan Facility 21,653 24,128 SEACOR Offshore Delta (f/k/a SEACOSCO) Acquisition Debt 19,705 — SEACOR Delta (f/k/a SEACOSCO) Shipyard Financing ( 2) 95,317 — SEACOR Alpine Shipyard Financing ( 3) 31,103 10,534 SEACOR 88/888 Term Loan 5,500 5,500 BNDES Equipment Construction Finance Notes - 3,332 Total recourse Long-term debt 399,028 282,244 Non-recourse Long-term debt ( 4) Falcon Global USA Term Loan Facility 102,349 102,349 Falcon Global USA Revolver 15,000 15,000 SEACOR 88/888 Term Loan 5,500 5,500 Total non-recourse Long-term debt 122,849 122,849 Total principal due for long-term debt 521,877 405,093 Current portion due within one year (32,377 ) (17,802 ) Unamortized debt discount (44,864 ) (26,343 ) Deferred financing costs (4,126 ) (5,234 ) Long-term debt, less current portion $ 440,510 $ 355,714 Long-Term Debt included in current liabilities associated with assets held for sale - Windcat Workboats Facilities $ 27,626 $ 24,537 (1) Recourse debt represents debt issued by SEACOR Marine and/or its subsidiaries and guaranteed by SEACOR Marine as defined in the relevant debt agreements. (2) SEACOR Delta Shipyard Financing includes vessel financing on the eight vessels acquired in the SEACOSCO Acquisition (see “Note 3. Business Acquisitions ”). (3) SEACOR Alpine Shipyard Financing includes vessel financing on the SEACOR Alps, the SEACOR Andes and the SEACOR Atlas vessels. (4) Non-recourse debt represents debt issued by the Company’s Consolidated Subsidiaries with no recourse to SEACOR Marine or its other non-debtor subsidiaries, other than certain limited support obligations as defined in the respective debt agreements, which in aggregate are not considered to be material to the Company’s business and financial condition. The Company’s contractual long-term debt maturities from continuing operations for the years ended December 31 were as follows (in thousands): 2021 $ 32,377 2022 38,484 2023 244,983 2024 134,523 2025 11,365 Years subsequent to 2025 60,145 $ 521,877 As of December 31, 2020, the Company is in compliance with all debt covenants and lender requirements. Falcon Global. On February 24, 2021, SEACOR Marine, Falcon Global USA LLC, an indirect wholly owned subsidiary of SEACOR Marine (“FGUSA”), and certain subsidiaries of FGUSA, entered into a Seventh Consent, Agreement and Omnibus Amendments (the “Seventh FGUSA Credit Facility Amendment”) to that certain (i) $131.1 million term and revolving loan facility, dated as of February 8, 2018, with a syndicate of lenders administered by JP Morgan Chase Bank, N.A. (as amended, the “FGUSA Credit Facility”) and (ii) obligation guaranty issued by SEACOR Marine, dated February 8, 2018, pursuant to which SEACOR Marine provides a guarantee of certain limited obligations of FGUSA under the Credit Facility (as amended, the “FGUSA Guaranty”). The Seventh FGUSA Credit Facility Amendment provides for, among other things, (i) the extension from March 2021 to June 2021 of the commencement of monthly repayment of the term loan, with payments being the lesser of (a) $0.8 million and (b) the amount outstanding under the term loan, (ii) the extension of the FGUSA Guaranty for an additional three months from February 8, 2021 to May 8, 2021, (iii) that the audited financial statements of FGUSA and its consolidated subsidiaries for the fiscal year ended December 31, 2020 are not required to be without a “going concern” or like qualification, commentary or exception, and (iv) the extension of the deadline for delivery of certain physical vessel appraisals from April 30, 2021 to December 31, 2021. Except as provided in the Guaranty, the FGUSA Credit Facility, is non-recourse to SEACOR Marine and its subsidiaries other than FGUSA . SEACOR Alpine. In 2019, the Company committed to take possession of three Rolls Royce UT1771 CDL designed diesel electric powered PSVs of 3,800 tons delivered deadweight capacity with dynamic position class 2 and firefighting class 1 notations. As part of this transaction, the shipbuilder, COSCO Shipping Heavy Industry (Zhoushan) Co. Ltd., agreed to finance 70% of the cost of each of these vessels pursuant to a deferred payment agreement. The deferred payment agreement calls for increasing quarterly payments of principal and interest payments that bear interest at an annual rate of 5% over a four-year Windcat Workboats. On March 3, 2020, Windcat Workboats, together with certain other obligors that are its subsidiaries entered into an agreement (the “RCF Amendment”) with Coöperatieve Rabobank U.A. to amend the €25 million revolving credit facility agreement, originally dated as of May 24, 2016, as amended and restated from time to time. Amended provisions included, among other things, the extension of the maturity date from December 31, 2021 to December 31, 2022. Applicable fees in the amount of €0.1 million were paid in conjunction with the RCF Amendment and will be amortized over the credit facility term. During the year ended December 31, 2020, the Company borrowed an additional €1.0 million under the Windcat Workboats credit facilities, resulting in a net increase in USD borrowings of $1.1 million. On December 18, 2020, the Company announced the sale of Windcat Workboats, which was completed on January 12, 2021. Upon completion of the sale, the Windcat Buyer assumed all financial obligations related to Windcat Workboats. The long-term debt obligations as of December 31, 2020 are classified as liabilities associated with assets held for sale. SEACOR Offshore Delta (f/k/a SEACOSCO). On June 30, 2020, the Company completed the acquisition of the SEACOSCO Interests that it did not already own. The deferred portion of the SEACOSCO Purchase Price is payable in annual installment payments of $1.0 million, $2.5 million and $2.5 million in the first, second and third year after the SEACOSCO SPA Signing Date, respectively, with the remaining $13.7 million due four years after such date. The deferred portion of the SEACOSCO Purchase Price accrues interest at a fixed rate of 1.5%, 7.0%, 7.5% and 8.0% for the first through fourth years after the signing date, respectively. The Guangdong DPAs comprising the SEACOR Delta Shipyard Financing provide for amortization of the purchase price for each vessel over a period of 10 years from delivery with the unpaid amount bearing floating interest rate of three-month LIBOR plus 4.0% (see “Note 3. Business Acquisitions”). SEACOR Marine Foreign Holdings. On September 26, 2018, SEACOR Marine Foreign Holdings Inc. (“SMFH”), a wholly-owned subsidiary of the Company, entered into a $130.0 million loan facility with a syndicate of lenders administered by DNB Bank ASA (as amended from time to time, the “SMFH Loan Facility”). Subject to Amendment No. 1, Amendment No. 2, Amendment No. 3 and the Letter Agreement described below, SMFH’s obligations pursuant to the SMFH Loan Facility were initially secured by mortgages on 20 vessels owned by the Company’s vessel owning subsidiaries as well as an assignment of earnings from those subsidiaries. The loan matures in 2023 and bears interest at a variable rate based on LIBOR (currently 4%). The obligations of SMFH under the SMFH Loan Facility are guaranteed by SEACOR Marine (the “SMFH Loan Facility Guaranty”). The proceeds from the SMFH Loan Facility were used to pay off all obligations under other credit facilities of subsidiaries of the Company (Falcon Global International Term Loan Facility, Sea-Cat Crewzer II Term Loan Facility, Sea-Cat Crewzer Term Loan Facility and C-Lift Acquisition Notes totaling $101.3 million, consisting of $99.9 million principal and $1.4 million accrued interest), resulting in a net increase in term debt of $30.1 million. Principal payments of $3.3 million per quarter under the SMFH Loan Facility began in December 2018. As a result of this transaction, the Company recognized a loss of $0.6 million upon the extinguishment of debt. In October 2018, the Company entered into an interest rate swap agreement on the notional value at inception of $65.0 million related to this debt. The SMFH Loan Facility provides for customary events of default and has customary affirmative and negative covenants for transactions of this type that are applicable to SEACOR Marine, SMFH and its subsidiaries. On August 6, 2019, SEACOR Marine, SMFH, and certain vessel-owning subsidiaries of SEACOR Marine, entered into Amendment No. 1 to the SMFH Loan Facility and SMFH Loan Facility Guaranty (the “Amendment No. 1”), which provided for, among other things, (i) the release of one vessel from a mortgage securing the SMFH Loan Facility and the substitution of mortgages over two other vessels owned by vessel-owning subsidiaries of SEACOR Marine, and (ii) the modification of certain financial maintenance and restrictive covenants contained in the SMFH Loan Facility or the SMFH Loan Facility Guaranty, including with respect to asset maintenance, vessel collateral releases, EBTIDA coverage ratios and the payment of dividends and distributions. On November 26, 2019, SEACOR Marine, SMFH, and certain vessel-owning subsidiaries of SEACOR Marine, entered into Amendment No. 2 to the SMFH Loan Facility, as amended (the “Amendment No. 2”), which provided for, among other things, (i) the release of six vessels from mortgages securing the SMFH Loan Facility and the substitution of mortgages over three other vessels owned by vessel-owning subsidiaries of SEACOR Marine and (ii) the bareboat registration in Nigeria of a vessel subject to a mortgage securing the SMFH Loan Facility. On June 29, 2020, SEACOR Marine, SMFH, and certain vessel-owning subsidiaries of SEACOR Marine, entered into Amendment No. 3 to the SMFH Loan Facility, as amended (the “Amendment No. 3”), which provides for, among other things, (i) the modification of certain financial maintenance and restrictive covenants contained in the SMFH Loan Facility or the guaranty provided by SEACOR Marine with respect thereto, including with respect to EBITDA coverage ratios, mandatory prepayment events, and the exclusion of certain indebtedness associated with the acquisition of the SEACOSCO Interests, and (ii) the placement of mortgages on two additional vessels owned by vessel-owning subsidiaries of SEACOR Marine as security for the indebtedness under the SMFH Loan Facility. On December 18, 2020, SEACOR Marine, SMFH and DNB Bank ASA, New York Branch, as facility agent on behalf of the lenders under the SMFH Loan Facility, and , entered into a letter agreement (the “Letter Agreement”) pursuant to which an estimated $31,200,000 tax refund receivable from the IRS under the Coronavirus Aid, Relief, and Economic Security Act (“CARES Act”) will be treated as cash or cash equivalents, for the period up to and including January 31, 2021, for purposes of calculating the Company’s cash or cash equivalent balances required under the . BNDES. In October 2019, Oceanpact purchased from the Company the two vessels securing the BNDES Equipment Construction Finance Notes, but the transfer of title of the vessels from the Company to Oceanpact was subject to the assignment of the BNDES Equipment Construction Finance Notes to Oceanpact. On June 9, 2020, Banco Nacional de Desenvolvimento Economico e Social (“BNDES”), a Brazilian government-owned entity, provided a suspension for a period of six months, from May 11, 2020 to October 10, 2020, on the payment of principal and compensatory interest under the BNDES Equipment Construction Finance Notes, without changing the final term of the debt amortization period nor the interest rate thereunder. Collection on the receivable balance from Oceanpact was also deferred. Oceanpact continued to work with BNDES to follow through with the assignment of the loan or accept another form of guarantee provided by Oceanpact in order to obtain a debt release from BNDES. On October 15, 2020, the Company’s outstanding debt balance to BNDES was paid in full and the receivable from OceanPact was paid in full. In addition, on October 23, 2020, the Company received a notification that the guarantor letter of credit had been released. The Company has no further obligations under the BNDES Equipment Construction Finance Notes. Convertible Senior Notes. On December 1, 2015, the Company issued $175.0 million in aggregate principal amount of its Convertible Senior Notes (the “Convertible Senior Notes”), at an interest rate of 3.75%, initially due December 1, 2022, (subsequently amended to December 2, 2023 as described below) to investment funds managed and controlled by the Carlyle Group (collectively “Carlyle”). The Convertible Senior Notes are convertible into shares of Common Stock at a conversion rate of 23.26 shares per $1,000 in principal amount of such notes, subject to certain conditions, or, into warrants to purchase an equal number of shares of Common Stock at an exercise price of $0.01 per share in order to facilitate the Company’s compliance with the provisions of the Jones Act. The indenture governing the Convertible Senior Notes contains customary events of default with respect to the Convertible Senior Notes. Upon completion of the Spin-off, the Company bifurcated the embedded conversion option liability of $27.3 million from the Convertible Senior Notes and recorded an additional debt discount (see “Note 10. Derivative Instruments and Hedging Strategies” and “Note 11. Fair Value Measurements”). The adjusted unamortized debt discount and issue costs are being amortized as additional non-cash interest expense over the remaining maturity of the debt for an overall effective interest rate of 7.95% and the changes in the fair value of the bifurcated derivative are recorded as derivative income or loss. On May 2, 2018, the Company and Carlyle entered into an exchange transaction (the “Exchange”) pursuant to which Carlyle exchanged $50 million in principal amount of the Convertible Senior Notes for Warrants to purchase 1,886,792 shares of Common Stock (to facilitate compliance with the provisions of the Jones Act) at an exercise price of $0.01 per share, subject to adjustments (the “Carlyle Warrants”), representing an implied exchange rate of approximately 37.73 shares per $1,000 in principal amount of the Convertible Senior Notes (equivalent to an exchange price of $26.50 per share). The Carlyle Warrants have a 25-year term, which commenced May 2, 2018. The Company and Carlyle also amended the $125.0 million in principal amount of Convertible Senior Notes that remained outstanding following the Exchange to (i) increase the interest rate from 3.75% per annum to 4.25% per annum and (ii) extend the maturity date of the Convertible Senior Notes by 12 months to December 1, 2023. Interest on the Convertible Senior Notes is payable semi-annually on June 15 and December 15 of each year. Sea-Cat Crewzer III Term Loan Facility. On April 21, 2016, Sea-Cat Crewzer III LLC ( “ Sea-Cat Crewzer III ” ) entered into a € 27.6 million term loan facility (payable in U . S . dollars) secured by the vessel owned by Sea-Cat Crewzer III and fully guaranteed by SEACOR Marine (the “Sea-Cat Crewzer III Loan Facility”) . Borrowings under the facility bear interest at a Commercial Interest Reference Rate, currently 2.76 %. During the years ended December 31, 2017 and 2016, Sea-Cat Crewzer III drew $ 7.1 million and $ 22.8 million, respectively, under the facility and incurred issue costs of $ 2.7 million in 2016 related to this facility. During the years ended December 31, 2018 Sea-Cat Crewzer III made scheduled payments of $ 3.1 million, related to this facility. On December 26, 2019, Sea-Cat Crewzer III, SEACOR Marine, Banco Santander S.A. (as mandated lead arranger and agent), and Santander Bank, N.A. (as lender) entered into A mendment N o. 1 to the Sea-Cat Crewzer III Loan Facility, which provide d for, among other things, an increase to the maximum debt to capitalization ratio required to be maintained thereunder. On December 24, 2020, Sea-Cat Crewzer III, SEACOR Marine, Banco Santander S.A. (as mandated lead arranger and agent), and Santander Bank, N.A. (as lender) entered into Amendment No. 2 to the Sea-Cat Crewzer III Loan Facility, which provided for, among other things, a waiver of the covenant breaches related to maximum debt to capitalization ratio and the exclusion of certain obligations of the g uarantor from the g uarantor’s n et f inancial debt for purposes of calculating the g uarantor’s permitted n et f inancial d ebt to e quity. The original loan agreement did not expressly exclude certain obligation of the g uarantor, including but not limited to non-recourse obligations. This amendment allows Sea-Cat Crewzer III to be in compliance with its debt agreements. SEACOR 88/888. On July 5, 2018, a wholly owned subsidiary of SEACOR Marine entered into a new term loan of $11.0 million and used the funds to acquire two vessels, the SEACOR 88 and SEACOR 888, that were previously managed (but not owned) by the Company. The term loan matures in 2023, bears interest at a variable rate (currently 3.75%) and is secured by the two vessels. SEACOR Marine provided a limited guaranty of such loan under which claims recoverable from SEACOR Marine shall not exceed the lesser of (x) $5.5 million and (y) 50% of the obligations outstanding at the time a claim is made thereunder. In October 2018, the Company entered into an interest rate swap agreement on the notional value at inception of $5.5 million related to this loan. Letters of Credit. As of December 31, 2020, the Company had outstanding letters of credit totaling $0.5 million for one lease obligation and labor and performance guarantees.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Income Taxes	9. INCOME TAXES In late 2017, the U.S. Tax Cuts and Jobs Act (the “Tax Act”) was enacted into law. This law significantly impacted our corporate income taxes commencing in 2018 and will continue to do so in future years. The most significant provisions included reducing the corporate tax rate from 35% to 21%; eliminating U.S. federal tax on dividends from foreign subsidiaries, creating a limitation on deductible interest expense, further restricting the compensation deduction, and changing the utilization of Net Operating Losses (“NOL’s”). In arriving at the 2020 results the Company took into account the impacts of the Tax Act based on our interpretation of the provisions enacted and the regulations issued as of this date On March 27, 2020 the Coronavirus Aid, Relief, and Economic Security Act (“CARES Act”) was enacted into law in response to the COVID-19 pandemic. The CARES Act lifts certain deduction limitations originally imposed by the 2017 Tax Act. Under the CARES Act, corporate taxpayers may carry back NOLs realized during 2018 through 2020 for up to five years. The CARES Act also eliminates the 80% of taxable income limitations by allowing corporate entities to fully utilize NOL carryforwards to offset taxable income in 2018 through 2020, and increased the deductible interest expense limit, as discussed in further detail below. As a result of the CARES Act, On June 26, 2020 the Company entered into a Tax Refund and Indemnification Agreement (the “Tax Refund Agreement”) with SEACOR Holdings, the Company’s former parent company (see “Note 17. Related Party Transactions”). SEACOR Holdings will retain certain of the funds to facilitate tax savings realized by SEACOR Holdings of no less than 35% of the amount of its own 2019 NOLs. Additionally, a $3.0 million transaction fee was paid to SEACOR Holdings concurrently with the signing of the agreement as consideration for its cooperation in connection with the filing of the applicable tax refund returns. As of December 31, 2020, the Tax Refund Agreement does not restrict the use of approximately $23.1 million of the refund, with the remaining approximately $8.1 million required to be deposited into an account to be used solely to satisfy certain of the Company’s obligations that remain guaranteed by SEACOR Holdings. Loss before income tax benefit and equity in earnings (losses) of 50% or less owned companies derived from U.S. and foreign companies for the years ended December 31 were as follows (in thousands): 2020 2019 2018 United States $ (83,560 ) $ (71,833 ) $ (72,540 ) Foreign (17,748 ) (23,663 ) (28,675 ) Eliminations 3,201 11,022 8,782 $ (98,107 ) $ (84,474 ) $ (92,433 ) The components of income tax expense (benefit) for the years ended December 31 were as follows (in thousands): 2020 2019 2018 Current: Federal $ (30,838 ) $ (6 ) $ 5,987 State 123 (78 ) 3 Foreign 5,533 5,005 3,307 (25,182 ) 4,921 9,297 Deferred: Federal 2,435 (12,594 ) (21,466 ) State (139 ) (224 ) (1,404 ) Foreign (38 ) (72 ) 110 2,258 (12,890 ) (22,760 ) $ (22,924 ) $ (7,969 ) $ (13,463 ) For the year ending December 31, 2020 For the year ending December 31, 2019, the Company recorded a return to provision adjustment related to losses from a consolidated joint venture for the 2018 tax year. The resulting additional liability of $2.3 million was recorded in the Company’s financial statements during the third quarter of 2019. For 2018, the Company incurred a current tax liability of $1.4 million related to the non-qualified withdrawal of funds from a Capital Construction Fund (“CCF”) by a partnership in which the Company held a 50% interest. The Company had previously recorded a deferred tax liability in connection with this CCF fund. The following table reconciles the difference between the statutory federal income tax rate for the Company and the effective income tax rate for the years ended December 31: 2020 2019 2018 Statutory rate (21.0 )% (21.0 )% (21.0 )% U.S. federal income tax law changes (11.8 )% — % — % SEACOR Holdings share awards to Company personnel 0.3 % — % 0.2 % Non-deductible expenses — % — % — % Exclusion of foreign subsidiaries with accumulated losses and withholding tax 7.7 % 7.4 % 9.3 % Noncontrolling interests 1.3 % 1.7 % (1.6 )% State taxes — % (0.3 )% (1.5 )% Return to provision (0.4 )% 2.8 % (0.5 )% Other 0.5 % — % 0.5 % Effective Tax Rate (23.4 )% (9.4 )% (14.6 )% For the year ending December 31, 2020, the Company’s effective income tax rate of 23.4% was primarily due to the effect of the NOL carrybacks pursuant to the CARES Act, foreign subsidiaries with current losses for which there is no federal income tax benefit, foreign taxes not creditable against U.S. income taxes, and taxes on income attributable to noncontrolling interests. For the year ending December 31, 2019, the Company’s effective income tax rate of 9.4% was lower than the statutory tax rate of 21% primarily due to foreign subsidiaries with current losses for which there is no federal income tax benefit, foreign taxes not creditable against U.S. income taxes, and noncontrolling interests. For the year ending December 31, 2018, the Company’s effective income tax rate of 14.6% was lower than the Company’s statutory tax rate of 21% primarily due to foreign subsidiaries with current losses for which there is no federal income tax benefit, foreign taxes not creditable against U.S. income taxes, and noncontrolling interests. The components of net deferred income tax liabilities as of December 31 were as follows (in thousands): 2020 2019 Deferred tax liabilities: Property and equipment $ 58,676 $ 63,827 Investments in 50% or Less Owned Companies 2,925 3,039 Other 4,819 10,612 Total deferred tax liabilities 66,420 77,478 Deferred tax assets: Federal Net Operating Loss Carryforwards 23,061 28,664 Other 10,073 16,561 33,134 45,225 Valuation Allowance (2,536 ) (1,311 ) Total deferred tax assets 30,598 43,914 Net deferred tax liabilities $ 35,822 $ 33,564 The Section 163(j) interest deduction limitations were amended to limit the ability of the Company to deduct net interest expense to thirty Future utilization of NOL’s arising in tax years after December 31, 2017 are limited to eighty As of December 31, 2020, the Company's valuation allowance of $2.5 million related primarily to foreign tax credit carryforwards which the Company expects to expire unutilized and Louisiana state net operating loss carryforwards.

Derivative Instruments and Hedg

Derivative Instruments and Hedging Strategies	12 Months Ended
	Dec. 31, 2020
Derivative Instruments And Hedging Activities Disclosure [Abstract]
Derivative Instruments and Hedging Strategies	10. DERIVATIVE INSTRUMENTS AND HEDGING STRATEGIES Derivative instruments are classified as either assets or liabilities based on their individual fair values. The fair values of the Company’s derivative instruments from continuing operations as of December 31 were as follows (in thousands): 2020 2019 Balance Sheet Classification Derivative Asset Derivative Liability Derivative Asset Derivative Liability Derivatives designated as hedging instruments: Interest rate swap agreements (cash flow hedges) Current $ — $ 3,698 $ — $ 2,925 — 3,698 — 2,925 Derivatives not designated as hedging instruments: Forward Exchange Contract Current — 893 — — Conversion option liability on Convertible Senior Notes Long-Term — 2 — 5,205 $ — $ 895 $ — $ 5,205 Economic Hedges. The Company enters and settles forward currency exchange, option and future contracts with respect to various foreign currencies. These contracts enable the Company to buy currencies in the future at fixed exchange rates, which could offset possible consequences of changes in currency exchange rates with respect to the Company’s business conducted outside of the U.S. The Company generally does not enter into contracts with forward settlement dates beyond twelve to eighteen months. During the year ended December 31, 2020, the Company recognized losses of $0.9 million on these contracts which were recognized concurrently in earnings and included in derivative liabilities in the accompanying consolidated balance sheets. Cash Flow Hedges. The Company and certain of its 50% or less owned companies have interest rate swap agreements designated as cash flow hedges at their inception. By entering into these interest rate swap agreements, the Company and its 50% or less owned companies have converted the variable LIBOR or EURIBOR component of certain of their outstanding borrowings to a fixed interest rate. The Company recognized losses on derivative instruments designated as cash flow hedges of $0.7 million for the year ended December 31, 2020, losses of $1.3 million for the year ended December 31, 2019 and gains of $1.6 million for the year ended December 31, 2018 as a component of other comprehensive loss. As of December 31, 2020, the interest rate swaps held by the Company and certain of the Company’s 50% or less owned companies were as follows: • Windcat Workboats had two interest rate swap agreements maturing in 2021 that call for the Company to pay a fixed rate of interest of (0.03%) plus margin on the aggregate notional value of €15.0 million ($20.4 million) and receive a variable interest rate based on EURIBOR on the aggregate notional value. The swap agreements are classified in liabilities associated with assets held for sale; • SEACOR Marine Foreign Holdings had an interest rate swap agreement maturing in 2023 that calls for SMFH to pay a fixed rate of interest of 3.32% plus margin on the amortized notional value of $7.8 million and receive a variable interest rate based on LIBOR on the amortized notional value; • SEACOR Marine Foreign Holdings had an interest rate swap agreement maturing in 2023 that calls for SMFH to pay a fixed rate of interest of 3.195% plus margin on the amortized notional value of $43.0 million and receive a variable interest rate based on LIBOR on the amortized notional value; • SEACOR 88/888 had an interest rate swap agreement maturing in 2023 that calls for Seacor 88/888 to pay a fixed rate of interest of 3.175% plus margin on the amortized notional value of $5.5 million and receive a variable interest rate based on LIBOR on the amortized notional value; and • MexMar, in which the Company has a 49% noncontrolling interest, had five interest rate swap agreements with maturities in 2023 that call for MexMar to pay a fixed rate of interest ranging from 1.71% to 2.10% per annum on the aggregate amortized notional value of plus margin on the aggregate amortized notional value of $69.4 million and receive a variable interest rate based on LIBOR on the aggregate amortized notional value. Derivative Instruments. The Company utilizes derivative instruments to manage the volatility of cash flows due to fluctuating interest rates. All derivative instruments not qualifying for the normal purchase and normal sale exception are recorded on the balance sheets at fair value. The treatment of the periodic changes in fair value will depend on whether the derivative is designated and effective as a hedge for accounting purposes. If a derivative qualifies for hedge accounting and is designated as a cash flow hedge, the effective portion of the change in fair value of the derivative is deferred in Accumulated Other Comprehensive Income (“AOCI”), a component of owners’ equity, and reclassified to earnings when the forecasted transaction occurs. Cash flows from a derivative instrument designated as a hedge are classified in the same category as the cash flows from the item being hedged. As such, we include the cash flows from interest rate derivative instruments in interest expense. If a derivative does not qualify as a hedge or is not designated as a hedge, the gain or loss resulting from the change in fair value on the derivative is recognized currently in earnings as a component of other income (expense). We formally document all relationships between hedging instruments and hedged items, as well as its risk management objectives and strategy for undertaking the hedge. This documentation includes the specific identification of the hedging instrument and the hedged item, the nature of the risk being hedged and the manner in which the hedging instrument’s effectiveness will be assessed. At the inception of the hedge, and on an ongoing basis, we assess whether the derivatives used in hedging transactions are highly effective in offsetting changes in cash flows of hedged items. The relationship between the hedging instrument and the hedged item must be highly effective in achieving the offset of changes in cash flows attributable to the hedged risk both at the inception of the contract and on an ongoing basis. We measure hedge ineffectiveness on a quarterly basis and reclassify any ineffective portion of the gain or loss related to the change in fair value to earnings in the current period. We will discontinue hedge accounting on a prospective basis when a hedge instrument is terminated or ceases to be highly effective. Gains and losses deferred in AOCI related to cash flow hedges for which hedge accounting has been discontinued remain deferred until the forecasted transaction occurs. If it is no longer probable that a hedged forecasted transaction will occur, deferred gains or losses on the hedging instrument are reclassified to earnings immediately. For balance sheet classification purposes, we analyze the fair values of the derivative instruments on a contract by contract basis and report the related fair values and any related collateral by counterparty on a gross basis. Realized and unrealized gains and losses on derivatives designated as cash flow hedges that are entered into by the Company’s 50% or less owned companies are also reported as a component of the Company’s other comprehensive loss in proportion to the Company’s ownership percentage, with reclassifications and ineffective portions being included in equity in earnings (losses) of 50% or less owned companies, net of tax, in the accompanying consolidated statements of loss. The fair value of our derivative instruments, depending on the type of instrument, was determined by the use of present value methods or standard option valuation models with assumptions about commodity prices based on those observed in underlying markets. The estimated fair value of our derivative instruments from continuing operations was a net liability of $4.6 million as of December 31, 2020. The estimated fair value is net of an adjustment for credit risk based on the default probabilities by year as indicated by market quotes for the counterparties’ credit default swap rates. The credit risk adjustment was $0.3 million at December 31, 2020. The following tables reflect amounts recorded in Other Comprehensive Income (Loss) (“OCI”) and amounts reclassified from OCI to revenue and expense for the periods indicated: Losses Recognized in OCI on Derivatives (Effective Portion) Derivatives in Cash Flow Hedging Relationships 2020 2019 2018 Interest rate swap contracts $ (2,139 ) $ (1,901 ) $ (1,939 ) Joint venture interest rate swap contracts (156 ) (645 ) (76 ) Losses Reclassified from OCI into Income (Effective Portion) Location of Loss 2020 2019 2018 Interest expense $ 1,425 $ 552 $ 31 Our consolidated earnings are also affected by the use of the mark-to-market method of accounting for derivative instruments that do not qualify for hedge accounting or that have not been designated as hedges. The changes in fair value of these instruments are recorded on the balance sheet and through earnings rather than being deferred until the anticipated transaction settles. The use of mark-to-market accounting for financial instruments can cause non-cash earnings volatility due to changes in the underlying commodity price indices. Other Derivative Instruments. The Company recognized gains (losses) on derivative instruments not designated as hedging instruments for the years ended December 31 as follows (in thousands): Derivative gains (losses), net 2020 2019 2018 Conversion option liability on Convertible Senior Notes $ 5,203 $ 71 $ 1,556 Interest rate swap agreements — — 1,298 Forward currency exchange, option and future contracts (893 ) — — $ 4,310 $ 71 $ 2,854 The conversion option liability relates to the bifurcated embedded conversion option in the Convertible Senior Notes (See “Note 8. Long-Term Debt”). The forward currency exchange contract relates to £31.5 million swap related to the proceeds to be received from the sale of Windcat Workboats (see “Note 4. Equipment Acquisitions and Dispositions”)

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2020
Fair Value Disclosures [Abstract]
Fair Value Measurements	11. The fair value of an asset or liability is the price that would be received to sell an asset or transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. The Company utilizes a fair value hierarchy that maximizes the use of observable inputs and minimizes the use of unobservable inputs when measuring fair value and defines three levels of inputs that may be used to measure fair value. Level 1 Level 2 Level 1 Level 3 The Company’s financial assets and liabilities as of December 31 that are measured at fair value on a recurring basis were as follows (in thousands): Level 1 Level 2 Level 3 (1) 2020 LIABILITIES Derivative instruments (included in other current liabilities) $ — $ 4,591 $ — Conversion Option Liability on Convertible Senior Notes — — 2 2019 ASSETS Construction reserve funds 12,893 — — LIABILITIES Derivative instruments (included in other current liabilities) — 2,925 — Conversion Option Liability on Convertible Senior Notes — — 5,205 (1) For the year ended December 31, 2020, the Company recognized a $5.2 million gain in the fair market valuation of the Conversion Option on the Convertible Senior Notes, as valued by an independent third-party. Level 3 Measurement. The fair value of the conversion option liability on the Convertible Senior Notes is estimated with significant inputs that are both observable and unobservable in the market and therefore is considered a Level 3 fair value measurement. The Company used a binomial lattice model that assumes the holders will maximize their value by finding the optimal decision between redeeming at the redemption price or converting into shares of Common Stock. This model estimates the fair value of the conversion option as the differential in the fair value of the notes including the conversion option compared with the fair value of the notes excluding the conversion option. The significant observable inputs used in the fair value measurement include the price of Common Stock and the risk-free interest rate. The significant unobservable inputs are the estimated Company credit spread and Common Stock volatility, which were based on comparable companies in the marine transportation and energy industries. The estimated fair value of the Company’s other financial assets and liabilities as of December 31 were as follows (in thousands): Estimated Fair Value Carrying Amount Level 1 Level 2 Level 3 2020 ASSETS Cash, cash equivalents and restricted cash $ 36,018 $ 36,018 $ — $ — Investments, at cost, in 50% or less owned companies (included in other assets) 132 see below LIABILITIES Long-term debt, including current portion 472,887 — 470,561 — 2019 ASSETS Cash, cash equivalents and restricted cash $ 84,486 $ 84,486 $ — $ — Investments, at cost, in 50% or less owned companies (included in other assets) 132 see below LIABILITIES Long-term debt, including current portion 373,516 — 356,086 — The carrying value of cash, cash equivalents and restricted cash approximates fair value. The fair value of the Company’s long-term debt was estimated by using discounted cash flow analysis based on estimated current rates for similar types of arrangements. It was not practicable to estimate the fair value of the Company’s investments, at cost, in 50% or less owned companies because of the lack of a quoted market price and the inability to estimate fair value without incurring excessive costs. Considerable judgment was required in developing certain of the estimates of fair value and, accordingly, the estimates presented herein are not necessarily indicative of the amounts that the Company could realize in a current market exchange. The Company’s non-financial assets and liabilities that were measured at fair value during the years ended December 31 were as follows (in thousands): Level 1 Level 2 Level 3 2020 ASSETS Property and equipment: Liftboats $ — $ 43,005 $ — 2019 ASSETS Property and equipment: AHTS $ — $ 520 $ — FSVs — 1,858 — Property and equipment. During the years ended December 31, 2020, 2019 and 2018 the Company recognized impairment charges of $18.8 million, $12.0 million, and $14.6 million, respectively, associated with certain offshore support vessels. The Level 2 fair values were determined based on the contracted sales prices of the property and equipment, sales prices of similar property and equipment or scrap value, as applicable. The Level 3 fair values were determined based on third-party valuations using significant inputs that are unobservable in the market. Due to limited market transactions, the primary valuation methodology applied by the appraisers was an estimated cost approach less estimated economic depreciation for comparably aged and conditioned assets less estimated economic obsolescence based on market data or utilization and rates per day worked trending of the vessels since 2014. Investments, at equity, in 50% or less owned companies. During the year ended December 31, 2020, the Company marked two of its investments in 50% or less owned companies, Seabulk Tims I and Offshore Vessel Holdings, to zero due to a return of funds that exceeded the carrying value of the investment and continued losses, respectively. The Company did not make any further adjustments to any of its investments in 50% or less owned companies

Warrants

Warrants	12 Months Ended
	Dec. 31, 2020
Warrants And Rights Note Disclosure [Abstract]
Warrants	12. WARRANTS In connection with various transactions, the Company issued 2,560,456 warrants to purchase shares of Common Stock at an exercise price of $0.01 per share (“Warrants”), of which 1,488,292 remain outstanding as of December 31, 2020. On September 1, 2020 and September 18, 2020, 255,307 and 83,367 Warrants were exercised, respectively, for a penny per share, resulting in 1,488,292 Warrants outstanding as of December 31, 2020. In connection with the exercise of Warrants on September 18, 2020, 354 shares of Common Stock were withheld as payment for the exercise price of the exercised Warrants. On May 28, 2019 and June 14, 2019, 380,000 and 64,440 Warrants were exercised, respectively, for a penny per share, resulting in 1,826,966 Warrants outstanding as of December 31, 2019. In connection with the exercise of Warrants on June 14, 2019, 49 shares of Common Stock were withheld as payment for the exercise price of the exercised Warrants.

Stockholders' Equity

Stockholders' Equity	12 Months Ended
	Dec. 31, 2020
Equity [Abstract]
Stockholders' Equity	13. On September 1, 2020 and September 18, 2020, 255,307 and 83,367 Warrants were exercised, respectively, for a penny per share, resulting in 1,488,292 Warrants outstanding as of December 31, 2020. In connection with the exercise of Warrants on September 18, 2020, 354 shares of Common Stock were withheld as payment for the exercise price of the exercised Warrants. The Company has previously registered 2,174,000 shares of Common Stock for issuance under the SEACOR Marine Holdings Inc. 2017 Equity Incentive Plan (the “2017 Plan”). The Company’s shareholders approved the SEACOR Marine Holdings Inc. 2020 Equity Incentive Plan (the “2020 Plan”) at the annual meeting of shareholders held on June 9, 2020 (the “Approval Date”), which authorized the issuance of 2,080,000 shares of Common Stock under the 2020 Plan. On June 9, 2020 the Company filed a registration statement on Form S-8 with the Securities and Exchange Commission (“SEC”) with respect to the registration of 2,114,821 shares of Common Stock, representing the 2,080,000 shares of Common Stock approved by the Company’s shareholders for issuance under the 2020 Plan, plus 24,821 shares of Common Stock remaining available for issuance under the 2017 Equity Incentive Plan as of the Approval Date that will be available for issuance under the 2020 Plan, plus Common Stock subject to awards outstanding under the 2017 Plan, that pursuant to the terms of the 2017 Plan and the 2020 Plan, may be available for future issuance under the 2020 Plan. On March 20, 2020, SEACOR LB Holdings LLC, an indirect wholly-owned subsidiary of SEACOR Marine (“SEACOR LB Holdings”), entered into a membership interest purchase agreement with SEACOR Marine, Montco Offshore, LLC (“Montco”) and Lee Orgeron, the principal of Montco, pursuant to which SEACOR LB Holdings purchased the 28% minority equity interest in Falcon Global Holdings held by Montco in exchange for 900,000 shares of Common Stock issued to Montco as consideration in a private placement. The purchase resulted in the Company owning 100% of Falcon Global Holdings. On May 28, 2019 and June 8, 2019, 380,000 and 64,440 Warrants were exercised, respectively, for a penny per share. In connection with the exercise of Warrants on June 14, 2019, 49 shares of Common Stock were withheld as payment for the exercise price of the exercised Warrants. On January 25, 2019, Seabulk Overseas Transport, Inc., a wholly owned subsidiary of SEACOR Marine (“Seabulk Overseas”), acquired a 6.25% minority interest in Windcat Workboats that it did not previously own upon the exercise of certain put options by one of the two minority owners pursuant to the terms of a subscription and shareholders agreement, as amended (the “Subscription and Shareholders Agreement”), in exchange for consideration of £1.6 million (approximately $2.0 million) in cash. The Company acquired the other 6.25% minority interest in Windcat Workboats that the Company did not already own on March 15, 2019 in exchange for consideration of 50,000 shares of Common Stock and €1.2 million (approximately $1.4 million) in cash. The Common Stock was issued in a private placement in reliance upon the exemption from registration provided by Section 4(a)(2) of the Securities Act. The two acquisitions resulted in Seabulk Overseas owning (and SEACOR Marine indirectly owning) 100% of Windcat Workboats. On January 9, 2019, certain indirect wholly owned subsidiaries of SEACOR Marine acquired three FSVs in exchange for the private placement of 603,872 shares of Common Stock to domestic U.S. holders affiliated with the McCall family of Louisiana. The value of the vessels and the Common Stock was $7.8 million based on the closing price of a share of Common Stock on the NYSE on the day of the exchange. The Common Stock was issued in reliance upon the exemption from registration provided by Section 4(a)(2) of the Securities Act. The Company has operated the acquired vessels for the past ten years under a revenue sharing pooling agreement that included four of its owned FSVs of similar specification. In accordance with its terms, this pooling agreement was terminated. On January 1, 2019, the Company adopted ASC 842 regarding the recording of lease on the balance sheet. This adoption resulted in an increase of $10.4 million, net of tax, to the Company’s opening retained earnings for the current period.

Noncontrolling Interests in Sub

Noncontrolling Interests in Subsidiaries	12 Months Ended
	Dec. 31, 2020
Noncontrolling Interest [Abstract]
Noncontrolling Interests in Subsidiaries	14. Noncontrolling interests in the Company’s consolidated subsidiaries as of December 31 were as follows (in thousands): Noncontrolling Interests 2020 2019 Falcon Global Holdings — % (1) $ — $ 21,119 Other 1.8 % 319 313 $ 319 $ 21,432 (1) Before March 20, 2020, noncontrolling interest was 28 % . Falcon Global Holdings. Prior to March 20, 2020, the Company held 72% of the equity interest in Falcon Global Holdings. On March 20, 2020, the Company completed the acquisition of the remaining 28% minority interest in Falcon Global Holdings, resulting in the Company’s 100% ownership of Falcon Global Holdings. Consideration paid by the Company was 900,000 shares of Common Stock issued in a private placement to the seller of the minority interest, Montco. Prior to the acquisition of the remaining noncontrolling interest in Falcon Global Holdings the net loss attributable to Falcon Global Holdings was $16.6 million, of which $4.6 million was attributable to noncontrolling interest

Savings and Multi-employer Pens

Savings and Multi-employer Pension Plans	12 Months Ended
	Dec. 31, 2020
Compensation And Retirement Disclosure [Abstract]
Savings and Multi-employer Pension Plans	15. SEACOR Marine Savings Plan. On January 1, 2016, the Company’s eligible U.S. based employees were transferred from the SEACOR Holdings sponsored defined contribution plan to the “SEACOR Marine 401(k) Plan,” a new Company sponsored defined contribution plan (the “Savings Plan”). Effective upon the June 1, 2017 Spin-off, the Company discontinued its contribution to the Savings Plan up until January 1, 2019, at which time the Company’s contribution were limited to 1% of an employee’s wages. In 2020, the Company increased its contributions to 2% of an employee’s wages. The Savings Plan costs for the year ended December 31, 2020 and 2019 were $0.3 million and $0.2 million, respectively. MNOPF and MNRPF. Certain of the Company’s subsidiaries are participating employers in two industry-wide, multi-employer, defined benefit pension funds in the United Kingdom: the U.K Merchant Navy Officers Pension Fund (“MNOPF”) and the U.K. Merchant Navy Ratings Pension Fund (“MNRPF”). The Company’s participation in the MNOPF began with the acquisition of the Stirling group of companies (the “Stirling Group”) in 2001 and relates to certain officers employed between 1978 and 2002 by the Stirling Group and/or its predecessors. The Company’s participation in the MNRPF also began with the acquisition of the Stirling Group in 2001 and relates to ratings employed by the Stirling Group and/or its predecessors through today. Both of these plans are in deficit positions and, depending upon the results of future actuarial valuations, it is possible that the plans could experience funding deficits that will require the Company to recognize payroll related operating expenses in the periods invoices are received. Under the direction of a court order, any funding deficit of the MNOPF is to be remedied through funding contributions from all participating current and former employers. Prior to 2015, the Company was invoiced and expensed $19.4 million for its allocated share of the then cumulative funding deficits, including portions deemed uncollectible due to the non-existence or liquidation of certain former employers. The invoiced amounts were re-paid in full, other than with respect to $2.6 million invoiced in 2013, for which the Company had a repayment plan with the trustees of the MNOPF to repay such invoice in full by December 31, 2023. As of December 31, 2020, the remaining liability due to the MNOPF had been settled in full. On November 7, 2018, the Company received notice from MNOPF that a deficit of £9.0 million existed but noted that the trustee did not propose to collect any additional funds in respect of such deficit. Depending on the results of future valuations, it is possible that the MNOPF will experience further funding deficits requiring the Company to recognize payroll related expenses in the periods the notice is received. The cumulative funding deficits of the MNRPF were being recovered by additional annual contributions from current employers that were subject to adjustment following the results of future tri-annual actuarial valuations. In 2015, the Company was invoiced and expensed $6.9 million for its share of a funding deficit in the MNRPF. The Company had a repayment plan with the trustees of the MNRPF for the amount to be repaid in full by October 30, 2018 and the amounts were settled by that date. On July 20, 2018, the Company was notified of additional contributions due and recognized in the second quarter of 2018 payroll related expenses of $1.2 million (£0.9 million) for its allocated share of the cumulative funding deficit including portions deemed uncollectible due to the non-existence or liquidation of certain former employers. As of December 31, 2020, all invoices related to the MNRPF have been settled in full. Depending upon the results of future actuarial valuations it is possible that the plan could experience further funding deficits that will require the Company to recognize payroll related operating expenses for those periods. Other Plans. Certain employees participate in other defined contribution plans in various international regions. During the years ended December 31, 2020, 2019 and 2018, the Company incurred costs, primarily from employer matching contributions of $0.4 million, $0.3 million and $0.2 million, respectively.

Share Based Compensation

Share Based Compensation	12 Months Ended
	Dec. 31, 2020
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Share Based Compensation	16. Equity Incentive Plan. During 2017, the Company adopted the SEACOR Marine Holdings Inc. 2017 Equity Incentive Plan (the “2017 Plan”). The 2017 Plan authorizes the Compensation Committee, or another committee designated by the Board and made up of two or more non-employee directors and outside directors, to provide equity-based or other incentive-based compensation for the purpose of attracting and retaining the Company and its affiliates’ directors, employees and certain consultants, and providing those directors, employees and consultants incentive opportunities and rewards for superior performance. The Board has authorized the issuance of 2,174,000 shares of Common Stock in connection with awards pursuant to the 2017 Plan, which was equal to 10% of the total number shares of Common Stock outstanding at the time of authorization. The types of awards under the 2017 Plan may include stock options, stock appreciation rights, restricted stock and restricted stock units, performance awards and other stock-based awards. The Company’s shareholders approved the SEACOR Marine Holdings Inc. 2020 Equity Incentive Plan (the “2020 Plan”) at the annual meeting of shareholders held on June 9, 2020 (the “Approval Date”), which authorized the issuance of 2,080,000 shares of Common Stock under the 2020 Plan. On June 9, 2020 the Company filed a registration statement on Form S-8 with the SEC with respect to the registration of 2,114,821 shares of Common Stock, representing the 2,080,000 shares of Common Stock approved by the Company’s shareholders for issuance under the 2020 Plan, plus 24,821 shares of Common Stock remaining available for issuance under the 2017 Plan as of the Approval Date that will be available for issuance under the 2020 Plan, plus shares of Common Stock subject to awards outstanding under the 2017 Plan, that pursuant to the terms of the 2017 Plan and the 2020 Plan, may be available for future issuance under the 2020 Plan. As of December 31, 2020, a total of 1,928,832 shares of Common Stock remained available for issuance under the 2020 Plan. Restricted stock typically vests from one to four years after the date of grant and options to purchase shares of Common Stock typically vest and become exercisable from one to four years after date of grant. Options to purchase shares of Common Stock granted under the 2017 Plan and the 2020 Plan expire no later than the tenth anniversary of the date of grant. In the event of a participant’s death, retirement, termination by the Company without cause or a change in control of the Company, as defined in the 2017 Plan, restricted stock vests immediately and in the event of participant’s death or retirement, options to purchase shares of Common Stock vest and become immediately exercisable. Distribution of SEACOR Marine Restricted Stock by SEACOR Holdings. Certain officers and employees of the Company previously received compensation through participation in SEACOR Holdings share award plans. Pursuant to the Employee Matters Agreement with SEACOR Holdings, participating Company personnel vested in all outstanding SEACOR Holdings share awards upon the Spin-off in 2017 and received SEACOR Marine restricted stock from the Spin-off distribution in connection with outstanding SEACOR Holdings restricted stock held. Therefore, the Company paid SEACOR Holdings $2.7 million upon completion of the Spin-off for the distribution of 120,693 shares of SEACOR Marine restricted stock, which is being amortized over the participants’ remaining original vesting periods. Employee Stock Purchase Plan. During 2017, the Company adopted the SEACOR Marine Holdings Inc. 2017 Employee Stock Purchase Plan (the “Marine ESPP”). The Marine ESPP, if implemented by the Company’s Board of Directors, will permit the Company to offer shares of its Common Stock for purchase by eligible employees at a price equal to 85% of the lesser of (i) the fair market value of a share of its Common Stock on the first day of the offering period or (ii) the fair market value of a share of its Common Stock on the last day of the offering period. There are 300,000 shares of the Company’s Common Stock reserved for issuance under the Marine ESPP during the ten years following its adoption. Share Award Transactions. The following transactions have occurred in connection with the Company’s share-based compensation under the 2017 Plan and the 2020 Plan during the years ended December 31: 2020 2019 Director Stock Awards Granted 59,900 30,197 Restricted Stock Activity: Outstanding as of the beginning of year 303,609 192,346 Granted 289,452 (1) 245,400 Vested 143,697 131,937 Forfeited 12,650 2,200 Outstanding as of the end of year 436,714 303,609 Stock Option Activity: Outstanding as of the beginning of year 913,569 805,566 Granted 261,972 230,503 Exercised — 113,750 Forfeited 55,000 8,750 Outstanding as of the end of year 1,120,541 913,569 (1) Excludes 240,800 grants of performance-based stock units that are not considered outstanding until such time that they become probable to vest. During the year ended December 31, 2020, the Company recognized $4.8 million of compensation expense related to stock awards, restricted stock and stock options granted to employees and directors under the 2017 Plan and the 2020 Plan. As of December 31, 2020, the Company had approximately $4.7 million in total unrecognized compensation costs. The weighted average period over which the compensation cost of non-vested awards will be recognized is approximately 1.24 and 0.89 years for restricted stock and stock options, respectively. During the year ended December 31, 2019, the Company recognized $5.3 million of compensation expense related to stock awards, restricted stock and stock options granted to employees and Directors under the 2017 Plan. As of December 31, 2018, the Company had approximately $6.5 million in total unrecognized compensation costs. During the year ended December 31, 2018, the Company recognized $4.4 million of compensation expense related to stock awards, restricted stock and stock options granted to employees and Directors under the 2017 Plan. As of December 31, 2018, the Company had approximately $6.8 million in total unrecognized compensation costs. The weighted average fair value of restricted stock granted under the 2017 Plan and the 2020 Plan were $6.40 and $13.28 for the year ended December 31, 2020 and 2019, respectively. The fair value was based the closing price of the Company’s stock on the day of the grant. The weighted average fair value of stock options granted under the 2017 Plan and the 2020 Plan was $3.60 and $8.73 for the year ended December 31, 2020 and 2019, respectively. The fair value of each option granted during the years ended December 31, 2020 and 2019, was estimated on the date of grant using the Black-Scholes option pricing model with the following assumptions: (a) no dividend yield; (b) weighted average expected volatility of 76.1 and 51.1, respectively; (c) weighted average discount rate of 0.52% and 2.1%, respectively; and (d) expected life of 9.92 and 9.75 years, respectively. The intrinsic value of stock options exercised during 2019 was $1.6 million. There were no stock options exercised in 2020. During the year ended December 31, 2020, the number of shares and the weighted average grant price of restricted stock transactions were as follows: Restricted Stock Number of Shares Weight Average Grant Price Non-Vested as of December 31, 2019 303,609 $ 20.46 Granted 289,452 6.81 Vested 143,697 13.43 Forfeited 12,650 12.30 Non-Vested as of December 31, 2020 436,714 11.60 During the year ended December 31, 2020, the number of shares and the weighted average exercise price on stock option transactions were as follows: Stock Options Number of Shares Weight Average Grant Price Non-Vested as of December 31, 2019 913,569 $ 14.81 Granted 261,972 3.68 Exercised — — Forfeited 55,000 13.43 Non-Vested as of December 31, 2020 1,120,541 12.49 Exercisable as of December 31, 2020 (1) 716,965 13.03 (1) The weighted average remaining contractual term is 8.18 years. As of December 31, 2020, there was no aggregate intrinsic value for options outstanding.

Related Party Transactions

Related Party Transactions	12 Months Ended
	Dec. 31, 2020
Related Party Transactions [Abstract]
Related Party Transactions	17. Transactions with SEACOR Holdings . In connection with the Spin-off, SEACOR Marine entered into certain agreements with SEACOR Holdings that govern SEACOR Marine’s relationship with SEACOR Holdings following the Spin-off, including a Distribution Agreement, two Transition Services Agreements, an Employee Matters Agreement and a Tax Matters Agreement. As of December 31, 2020, SEACOR Holdings had guaranteed $8.1 million for various obligations of the Company, including performance obligations under sale-leaseback arrangements (see “Note 7. Leases”). On June 26, 2020, the Company entered into a Tax Refund and Indemnification Agreement (the “Tax Refund Agreement”) with SEACOR Holdings Inc. (“SEACOR Holdings”), the Company’s former parent company. The Tax Refund Agreement will enable the Company to utilize net operating losses (“NOLs”) generated in 2018 and 2019 to claim refunds for tax years prior to the Company’s spin-off from SEACOR Holdings in 2017 (at which time the Company was included in SEACOR Holdings consolidated tax returns) that are now permitted to be carried back pursuant to the provisions of the CARES Act and for which SEACOR Holdings needs to claim the refund on behalf of the Company. As a result, the Company expects to receive cash tax refunds of approximately $31.2 million within the next 12 months, subject to the refund schedule of the IRS. The IRS has been recently experiencing delays in processing refund claims due in part to the COVID-19 pandemic. SEACOR Holdings will retain certain of the funds to facilitate tax savings realized by SEACOR Holdings of no less than 35% of the amount of its own 2019 NOLs. Additionally, a $3.0 million transaction fee was paid to SEACOR Holdings concurrently with the signing of the Tax Refund Agreement as consideration for its cooperation in connection with the filing of the applicable tax refund returns. As of December 31, 2020, the Tax Refund Agreement does not restrict the use of approximately $23.1 million of the refund, with the remaining approximately $8.1 million required to be deposited into an account to be used solely to satisfy certain of the Company’s obligations that remain guaranteed by SEACOR Holdings which primarily relate to vessel operating leases. Two of these vessel operating leases expired in the fourth quarter of 2020, reducing the remaining guarantee on the three remaining vessels to $7.0 million. The remaining three vessel operating leases that SEACOR Holdings guarantees expire in 2021 and the Company will apply the amount deposited to satisfy these obligations. Following the completion of the Spin-off, the Company is no longer charged for management fees or shared services allocation (see below) for administrative support by SEACOR Holdings; however, the Company continued to be supported by SEACOR Holdings for corporate services pursuant to the Transition Services Agreements with SEACOR Holdings under which it was initially charged $6.3 million annually for these services. The fees incurred have declined as the services and functions provided by SEACOR Holdings are terminated and replicated within the Company. For the year ended December 31, 2019 and 2018 the Company incurred fees of $0.6 million, and $4.5 million, Transactions regarding OSV Partners . Charles Fabrikant (Non-Executive Chairman of SEACOR Marine), John Gellert (President, Chief Executive Officer and Director of SEACOR Marine), Jesús Llorca (Executive Vice President and Chief Financial Officer of SEACOR Marine), other members of the Company ’ s management and B oard of D irectors and other unaffiliated individuals indirectly invested in OSV Partners by purchasing interests from three unaffiliated limited partners of OSV Partners who wished to dispose of their interests. During 2018, OSV Partners (i) raised $ 7.5 million of cash: $ million in the f orm of second lien debt and $ 2.5 million in the form of class A preferred interests and (ii) obtained commitments fr o m the limited partners of OSV Partners for an additional $ 2.5 million in the form of C lass A preferred interest s . On December 18 , 20 19 , the general partner of OSV Partners called these remaining commitments . As of December 31, 20 20 , limited liability companies controlled by management and D irectors of the Company had invested $ 1.5 million, or 3.9 %, in the limited partner interests; $ 0.3 million, or 5.0 %, in preferred interests; $ 0.2 million, or 3.9 %, in the form of second lien debt; and $ million, or 3.9 %, in the Cl ass A preferred interests of OSV Partners. A s of December 31, 20 20 , the investments of Messrs. Fabrikant , Gellert and Llorca in such limited liability companies were $ 0.3 million , $ 0.4 million and $ million, respectively, representing % of such limited liability companies ’ membership interests. The general partner of OSV Partners is a joint venture managed by the Company and an unaffiliated third-party. The Company owns 30.4 % in the limited partner interests, 38.6 % in the preferred interests, 43.0 % of the second lien debt, and 43.0 % in the C lass A preferred interest of OSV Partners . The Company agreed to not charge OSV Partners the management fee it is contractually entitled to through December 31, 2020. Transactions regarding Windcat Workboats . On January 25, 2019, Seabulk Overseas acquired a 6.25% minority interest in Windcat Workboats that it did not previously own upon the exercise of a put option by one of the two minority owners, each of whom was a member (or an affiliate of a member) of management of Windcat Workboats at the time of acquisition, pursuant to the terms of a certain Subscription and Shareholders Agreement, as amended, for consideration of £1.6 ($2.0 million). On March 15, 2019, Seabulk Overseas acquired the other 6.25% minority interest in Windcat Workboats that it did not previously own for consideration of 50,000 shares of Common Stock and €1.2 million (approximately $1.4 million) in cash. The two acquisitions resulted in Seabulk Overseas owning 100% of Windcat Workboats, a consolidated subsidiary which owns and operates the Company’s CTV business that is primarily used to move personnel and supplies in Europe’s offshore wind markets On January 12, 2021, a wholly owned subsidiary of SEACOR Marine, completed the sale of the Windcat Workboats CTV business through the sale of 100% of the equity of Windcat Workboats to CMB N.V. pursuant to a Sale and Purchase Agreement entered into on December 18, 2020 (see “Note 1. Nature of Operations and Accounting Policies” and “Note 4. Equipment Acquisitions and Dispositions”). Transactions with Carlyle . On December 1, 2015, the Company issued $175.0 million aggregate principal amount of its Convertible Notes to investment funds managed and controlled by Carlyle. Interest on the Convertible Notes is payable semi-annually on June 15 and December 15 of each year, commencing June 15, 2016 (see “Note 8. Long-Term Debt”). Pursuant to the note purchase agreement for the Convertible Notes and the Investment Agreement, the Company must use reasonable best efforts, subject to its directors’ fiduciary duties, to cause a person designated by Carlyle to be appointed as a director on the Board of Directors, if Carlyle, solely as a result of the conversion of the Convertible Notes, collectively owns, continues to own, or would (upon conversion) own 10.0% or more of the Company’s outstanding shares of Common Stock. During 2017, Ferris Hussein served on the Board of Directors as the director designated by Carlyle until his resignation on April 17, 2018. Carlyle has not exercised this right subsequent to Mr. Hussein’s resignation but retains the right to appoint a member to the Board of Directors. Mr. Hussein has been designated by Carlyle to observe meetings of the Board of Directors pursuant to Carlyle’s observer rights under the Convertible Notes. This observation right will terminate at the time Carlyle owns less than $50.0 million in aggregate principal amount of the Convertible Notes or a combination of the Convertible Notes and our Common Stock representing less than 5.0% of the Company’s Common Stock outstanding on a fully diluted basis, assuming the conversion of all of the Convertible Notes and Warrants to purchase Common Stock held by Carlyle. In April 2018, the Company entered into the following Exchange and other transactions with Carlyle pursuant to which: • the Company exchanged $50.0 million in principal amount of the Convertible Notes for Common Stock (or warrants to purchase an equivalent number of shares of Common Stock at an exercise price of $0.01 per share) at an exchange rate of 37.73 per $1,000 principal amount of the Notes (equivalent to an exchange price of $26.50) for a total of approximately 1.9 million shares of Common Stock including Common Stock issuable upon exercise of the Exchange Warrants (the “Exchange”); • the Company and Carlyle amended the $125.0 million in principal amount of Convertible Notes that remains outstanding after the Exchange to (i) increase the interest rate from 3.75% per annum to 4.25% per annum and (ii) extend the maturity of the Convertible Notes by 12 months to December 1, 2023; • Carlyle purchased 750,000 shares of Common Stock in a private placement whereby the Company issued an aggregate of 2,168,586 shares of Common Stock and warrants to purchase 674,164 shares of Common Stock at an exercise price of $0.01 per share in a private placement exempt from registration under the Securities Act (the “PIPE Issuance”) for aggregate consideration of $15.0 million; and • During 2020 and 2019, Carlyle exercised 83,367 and 64,440 warrants, respectively. As of December 31, 2020, Carlyle still has 1,488,292 outstanding warrants. Transactions with CME . Mr. Alfredo Miguel Bejos, a Director of SEACOR Marine, currently serves as President and Chief Executive Officer of CME. During 2020 and 2019, CME exercised 255,307 and 380,000 warrants, respectively. As of December 31, 2020, all of CME’s outstanding warrants have been exercised. On December 20, 2018, MEXMAR Offshore, a joint venture that is 49.0% owned by a subsidiary of the Company and 51.0% owned by a subsidiary of CME, acquired UP Offshore. UP Offshore was acquired for nominal consideration. In connection with the acquisition, UP Offshore’s existing debt was refinanced with $95.0 million of new indebtedness composed of (i) a $70.0 million six-year debt facility provided by UP Offshore’s existing lenders that is non-recourse to the Company, CME or any of their respective subsidiaries, (ii) a $15.0 million loan from MexMar, a joint venture between CME and the Company, to fund capital expenditures on two vessels and (iii) a $10.0 million loan from MEXMAR Offshore to fund working capital requirements funded by an approximate $5.0 million capital contribution to MEXMAR Offshore by each of the Company and CME. Due to losses from equity earnings, the Company’s investment in MEXMAR Offshore was written down to $0 in 2019. In July 2020, MEXMAR Offshore purchased from a consortium of banks in Brazil, $70 million of UP Offshore’s debt for $5.5 million, of which the Company’s commitment was $2.7 million to fund this purchase. As of December 31, 2020, the Company had loaned its proportional share of this commitment to MEXMAR Offshore of $1.96 million. The Company funded its remaining commitment in February 2021. The Company also participates in a variety of other joint ventures with CME, including MexMar, SEACOR Marlin and OVH. These agreements with MexMar were negotiated at arms-length in the ordinary course of business. In 2019, the Company sold an FSV to OVH for $2.4 million through a seller’s finance agreement. Transaction with Talos Energy Inc Mr. Robert D. Abendschein, a Director of SEACOR Marine, currently serves as Executive Vice President and Head of Operations of Talos Energy Inc. (together with its subsidiaries and affiliates, “Talos Energy”). Talos Energy is a customer of the Company and its subsidiaries, primarily with respect to the chartering of liftboats and other vessels. The Company recognized $1.5 million, $3.2 million and $2.9 million in revenue with Talos Energy in 2020, 2019 and 2018, respectively.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2020
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	18. COMMITMENTS AND CONTINGENCIES As of December 31, 2020, the Company’s unfunded capital commitments from continuing operations were $11.7 million for one PSV and miscellaneous vessel equipment. Of the unfunded capital commitments, $10.7 million is payable during 2021 and $1.0 million is payable during 2022. As of December 31, 2020, the Company had indefinitely deferred an additional $9.6 million of orders with respect to one FSV that the Company had previously reported as an unfunded capital commitments. In December 2015, the Brazilian Federal Revenue Office issued a tax-deficiency notice to Seabulk Offshore do Brasil Ltda, an indirect wholly-owned subsidiary of SEACOR Marine (“Seabulk Offshore do Brasil”), with respect to certain profit participation contributions (also known as “PIS”) and social security financing contributions (also known as “COFINS”) requirements alleged to be due from Seabulk Offshore do Brasil (“Deficiency Notice”) in respect of the period of January 2011 until December 2012. In January 2016, the Company administratively appealed the Deficiency Notice on the basis that, among other arguments, (i) such contributions were not applicable in the circumstances of a 70%/30% cost allocation structure, and (ii) the tax inspector had incorrectly determined that values received from outside of Brazil could not be classified as expense refunds. The initial appeal was dismissed by the Brazilian Federal Revenue Office and the Company appealed such dismissal and is currently awaiting an administrative trial. Recently, a local Brazilian law was enacted that supports the Company’s position that such contribution requirements are not applicable, but it is uncertain whether such law will be taken into consideration with respect to administrative proceedings commenced prior to the enactment of the law. Accordingly, the success of Seabulk Offshore do Brasil in the administrative proceedings cannot be assured and the matter may need to be addressed through judicial court proceedings. The potential levy arising from the Deficiency Notice is R$18.12 million based on a historical potential levy of R$12.87 million (USD $3.5 million and USD $2.5 million, respectively, based on the exchange rate as of December 31, 2020). For a discussion of the Company’s potential obligations with respect to the MNOPF and MNRPF, see “Note 15. Savings and Multi-Employer Pension Plan.” In the normal course of its business, the Company becomes involved in various other litigation matters including, among other things, claims by third parties for alleged property damages and personal injuries. Management has used estimates in determining the Company ’ s potential exposure to these matters and has recorded reserves in its financial statements related thereto where appropriate. It is possible that a change in the Company ’ s estimates of that exposure could occur, but the Company does not expect such changes in estimated costs could have a material adverse effect on the Company ’ s business, financial position, results of operations, cash flows and prospects.

Major Customers and Segment Inf

Major Customers and Segment Information	12 Months Ended
	Dec. 31, 2020
Notes To Financial Statements [Abstract]
Major Customers and Segment Information	19. During the year ended December 31, 2020, two customers, SEACOR Marine Arabia LLC, a joint venture through which vessels are in service to Saudi Aramco, and Exxon Mobil were each responsible for $30.7 million or 21% and $24.8 million or 17%, respectively, of the Company’s total consolidated operating revenues from continuing operations. During the year ended December 31, 2019, SEACOR Marine Arabia LLC was responsible for $30.8 million or 17% ($20.3 million or 11% from Zamil Offshore and $10.5 million or 6% from Saudi Aramco) of the Company’s total consolidated operating revenues from continuing operations. During the year ended December 31, 2018, SEACOR Marine Arabia LLC was responsible for $21.4 million or 12% ($12.2 million or 7% from Zamil Offshore and $9.2 million or 5% from Saudi Aramco) of the Company’s total consolidated operating revenues from continuing operations. Additionally, Exxon Mobil was responsible for revenues of $16.5 million or 9% and $3.1 million or 2% in 2019 and 2018, respectively. For the years ended December 31, 2020, 2019 and 2018, the ten largest customers of the Company accounted for approximately 76%, 61%, and 57%, respectively, of the Company’s operating revenues from continuing operations. The loss of one or more of these customers could have a material adverse effect on the Company’s results of operations and cash flows. For the years ended December 31, 2020, 2019 and 2018, approximately 89%, 75%, and 71%, respectively, of the Company’s operating revenues and ($6.6) million, ($13.0) million, and ($1.9) million, respectively, of equity in losses from 50% or less owned companies, net of tax, were derived from its continuing foreign operations. The Company’s offshore support vessels are highly mobile and regularly and routinely move between countries within a geographic region of the world. In addition, these vessels may be redeployed among the geographic regions, subject to flag restrictions, as changes in market conditions dictate. Because of this asset mobility, operating revenues and long-lived assets in any one country and capital expenditures for long-lived assets and gains or losses on asset dispositions and impairments in any one geographic region are not considered meaningful. The following tables summarize (in thousands) the operating results and property and equipment of the Company’s reportable segments. Direct vessel profit is the Company’s measure of segment profitability, a key metric in assessing the performance of its fleet. Direct vessel profit is defined as operating revenues less direct operating expenses excluding leased-in equipment expense. The Company utilizes direct vessel profit as its primary financial measure to analyze and compare the operating performance of its individual vessels, fleet categories, regions and combined fleet. United States (primarily Gulf of Mexico) Africa (primarily West Africa) Middle East and Asia Latin America Europe Continuing Operations Total For the year ended December 31, 2020 Operating Revenues: Time charter $ 9,873 $ 35,876 $ 52,052 $ 23,806 $ 11,847 $ 133,454 Bareboat charter 2,910 — — — (55 ) 2,855 Other 2,422 (465 ) 2,157 1,084 330 5,528 15,205 35,411 54,209 24,890 12,122 141,837 Direct Costs and Expenses: Operating: Personnel 10,065 10,552 18,188 6,698 2,845 48,348 Repairs and maintenance 1,655 5,175 5,232 2,131 468 14,661 Drydocking 1,167 2,014 759 329 — 4,269 Insurance and loss reserves 1,774 1,026 1,721 462 780 5,763 Fuel, lubes and supplies 1,172 2,940 2,706 990 320 8,128 Other 373 984 6,891 1,369 359 9,976 16,206 22,691 35,497 11,979 4,772 91,145 Direct Vessel (Loss) Profit $ (1,001 ) $ 12,720 $ 18,712 $ 12,911 $ 7,350 50,692 Other Costs and Expenses: Operating: Leased-in equipment $ 4,272 $ 3,029 $ 170 $ 45 $ 9 7,525 Administrative and general 40,051 Depreciation and amortization $ 21,427 $ 10,833 $ 16,595 $ 5,481 $ 2,831 57,167 104,743 Losses on Asset Dispositions and Impairments, Net (17,588 ) Operating Loss $ (71,639 ) As of December 31, 2020 Property and Equipment: Historical cost $ 257,592 $ 204,079 $ 361,514 $ 130,769 $ 58,919 $ 1,012,873 Accumulated depreciation (134,391 ) (60,535 ) (75,349 ) (13,312 ) (7,951 ) (291,538 ) $ 123,201 $ 143,544 $ 286,165 $ 117,457 $ 50,968 $ 721,335 Total Assets ( 1) $ 164,656 $ 153,399 $ 289,314 $ 179,942 $ 74,495 $ 861,806 (1) Total assets exclude $105.6 million of corporate assets, and $50.2 million of assets held for sale. United States (primarily Gulf of Mexico) Africa (primarily West Africa) Middle East and Asia Latin America Europe Continuing Operations Total For the year ended December 31, 2019 Operating Revenues: Time charter $ 38,955 $ 44,160 $ 54,312 $ 11,460 $ 8,165 $ 157,052 Bareboat charter 1,562 — — 3,569 — 5,131 Other 3,806 1,461 1,669 1,390 3,944 12,270 44,323 45,621 55,981 16,419 12,109 174,453 Direct Costs and Expenses: Operating: Personnel 17,491 13,833 16,698 4,459 3,494 55,975 Repairs and maintenance 7,583 4,701 7,182 1,348 587 21,401 Drydocking 4,594 490 600 161 3 5,848 Insurance and loss reserves 2,370 1,051 1,449 311 441 5,622 Fuel, lubes and supplies 2,936 3,471 2,904 1,056 255 10,622 Other 393 4,354 3,095 1,182 1,031 10,055 35,367 27,900 31,928 8,517 5,811 109,523 Direct Vessel Profit $ 8,956 $ 17,721 $ 24,053 $ 7,902 $ 6,298 64,930 Other Costs and Expenses: Operating: Leased-in equipment $ 10,894 $ 3,090 $ 173 $ 10 $ 1,673 15,840 Administrative and general 39,791 Depreciation and amortization $ 21,947 $ 10,404 $ 16,400 $ 6,205 $ 2,210 57,166 112,797 Losses on Asset Dispositions and Impairments, Net (6,461 ) Operating Loss $ (54,328 ) As of December 31, 2019 Property and Equipment: Historical cost $ 297,392 $ 207,107 $ 292,446 $ 57,534 $ 44,545 $ 899,024 Accumulated depreciation (157,514 ) (57,136 ) (73,039 ) (16,239 ) (4,989 ) (308,917 ) $ 139,878 $ 149,971 $ 219,407 $ 41,295 $ 39,556 $ 590,107 Total Assets ( 1) $ 224,229 $ 161,915 $ 250,890 $ 116,736 $ 64,156 $ 817,926 (1) Total assets exclude $145.5 million of corporate assets, and $45.7 million of assets held-for-sale United States (primarily Gulf of Mexico) Africa (primarily West Africa) Middle East and Asia Latin America Europe Continuing Operations Total For the year ended December 31, 2018 Operating Revenues: Time charter $ 38,802 $ 43,847 $ 50,072 $ 17,343 $ — $ 150,064 Bareboat charter — — — 4,635 — 4,635 Other 14,762 7,661 (887 ) 1,554 1,372 24,462 53,564 51,508 49,185 23,532 1,372 179,161 Direct Costs and Expenses: Operating: Personnel 18,708 16,538 16,806 4,399 2,081 58,532 Repairs and maintenance 5,152 6,330 11,172 1,011 720 24,385 Drydocking 1,957 2,085 1,362 128 2,260 7,792 Insurance and loss reserves 2,922 1,096 1,371 495 86 5,970 Fuel, lubes and supplies 3,568 3,826 4,027 1,225 258 12,904 Other 393 4,313 3,980 1,130 188 10,004 32,700 34,188 38,718 8,388 5,593 119,587 Direct Vessel Profit (Loss) $ 20,864 $ 17,320 $ 10,467 $ 15,144 $ (4,221 ) 59,574 Other Costs and Expenses: Operating: Leased-in equipment $ 8,240 $ 4,281 $ 224 $ 5 $ 214 12,964 Administrative and general 41,616 Depreciation and amortization $ 23,227 $ 10,453 $ 18,762 $ 7,908 $ 1,069 61,419 115,999 Losses on Asset Dispositions and Impairments, Net (11,989 ) Operating Loss $ (68,414 ) As of December 31, 2018 Property and Equipment: Historical cost $ 432,336 $ 184,361 $ 306,897 $ 124,177 $ 26 $ 1,047,797 Accumulated depreciation (224,737 ) (55,206 ) (81,378 ) (57,002 ) (17 ) (418,340 ) $ 207,599 $ 129,155 $ 225,519 $ 67,175 $ 9 $ 629,457 Total Assets ( 1) $ 351,748 $ 140,335 $ 260,002 $ 137,983 $ (28,450 ) 861,618 (1) Total assets exclude $153.1 million of corporate assets, and $88.2 million of assets held-for-sale.

Discontinued Operations

Discontinued Operations	12 Months Ended
	Dec. 31, 2020
Discontinued Operations And Disposal Groups [Abstract]
Discontinued Operations	2 0 . DISCONTINUED OPERATIONS On January 12, 2021, the Company completed the sale of Windcat Workboats, which on December 31, 2020 was classified as current assets held for sale. The Company’s discontinued operations as of December 31, 2019, consisted of both Windcat Workboats and Boston Putford Offshore Safety. The Company has no continuing involvement in either of these businesses, which is considered a strategic shift in the Company’s operations. Summarized selected operating result of the Company’s assets held for sale and discontinued operations were as follows for the years ended December 31, (in thousands): 2020 2019 Assets from Discontinued Operations: Current assets $ 10,138 $ 9,603 Net property and equipment 34,580 31,447 Non-current assets 5,517 4,668 50,235 45,718 Liability from Discontinued Operations: Current liabilities $ 2,418 $ 2,060 Long-term liabilities 28,509 25,480 $ 30,927 $ 27,540 Windcat Workboats Boston Putford Offshore Safety 2020 2019 2020 2019 Operating Revenues: Time charter $ 29,383 $ 25,249 $ — $ 41,214 Other revenue 2,305 1,790 — 45 31,688 27,039 — 41,259 Costs and Expenses: Operating 17,334 14,202 — 33,836 Direct Vessel Profit 14,354 12,837 — 7,423 General and Administrative Expenses 5,516 4,935 — 4,207 Lease Expense 628 318 — 60 Depreciation 6,166 6,846 — 3,504 Gains on Asset Dispositions and Impairments, Net — 1,064 — 91 Operating Income (Loss) 2,044 1,802 — (257 ) Other Income (Expense) Interest income 59 56 — 11 Interest expense (1,115 ) (1,100 ) — (210 ) Foreign currency translation (loss) gain (750 ) 880 — (75 ) Other, net 19 — — — (1,787 ) (164 ) — (274 ) Operating Income (Loss) Before Equity Earnings of 50% or Less Owned Companies, Net of Tax 257 1,638 — (531 ) Income Tax (Benefit) Expense (86 ) 57 — (2 ) Operating Income (Loss) Before Equity Earnings of 50% or Less Owned Companies 343 1,581 — (529 ) Equity in Earnings of 50% or Less Owned Companies, Net of Tax 21 155 — 168 Net Income (Loss) from Discontinued Operations $ 364 $ 1,736 $ — $ (361 )

Quarterly Financial Information

Quarterly Financial Information (Unaudited)	12 Months Ended
	Dec. 31, 2020
Quarterly Financial Information Disclosure [Abstract]
Quarterly Financial Information	21. Selected financial information for interim quarterly periods is presented below (in thousands, except share data). Earnings (loss) per common share of SEACOR Marine Holdings Inc. are computed independently for each of the quarters presented and the sum of the quarterly earnings per share may not necessarily equal the total for the year. Three Months Ended Dec. 31, Sept. 30, June 30, March 31, 2020 Operating Revenues $ 36,044 $ 36,201 $ 33,925 $ 35,667 Operating Loss (16,915 ) (13,179 ) (17,824 ) (23,721 ) Net (Loss) Income: Continuing Operations (38,898 ) (19,842 ) (6,668 ) (17,938 ) Discontinued Operations 51 1,765 602 (2,054 ) $ (38,847 ) $ (18,077 ) $ (6,066 ) $ (19,992 ) Net Loss attributable to SEACOR Marine Holdings Inc: $ (38,816 ) $ (18,081 ) $ (6,073 ) $ (15,945 ) Basic and Diluted (Loss) Income Per Common Share of SEACOR Marine Holdings Inc. Continuing Operations $ (1.54 ) $ (0.79 ) $ (0.26 ) $ (0.58 ) Discontinued Operations $ — $ 0.07 $ 0.02 $ (0.08 ) $ (1.54 ) $ (0.72 ) $ (0.24 ) $ (0.66 ) 2019 Operating Revenues $ 42,478 $ 46,996 $ 45,014 $ 39,965 Operating Loss (10,555 ) (5,566 ) (18,591 ) (19,616 ) Net (Loss) Income: Continuing Operations (19,439 ) (12,586 ) (31,632 ) (27,307 ) Discontinued Operations (2,479 ) (5,654 ) 1,368 (966 ) $ (21,918 ) $ (18,240 ) $ (30,264 ) $ (28,273 ) Net Loss attributable to SEACOR Marine Holdings Inc: $ (20,455 ) $ (18,444 ) $ (28,389 ) $ (25,549 ) Basic and Diluted (Loss) Income Per Common Share of SEACOR Marine Holdings Inc. Continuing Operations $ (0.76 ) $ (0.54 ) $ (1.27 ) $ (1.07 ) Discontinued Operations $ (0.10 ) $ (0.24 ) $ 0.06 $ (0.04 ) $ (0.86 ) $ (0.78 ) $ (1.21 ) $ (1.11 ) 121

Schedule II - Valuation and Qua

Schedule II - Valuation and Qualifying Accounts	12 Months Ended
	Dec. 31, 2020
Valuation And Qualifying Accounts [Abstract]
Schedule II - Valuation and Qualifying Accounts	SEACOR MARINE HOLDINGS INC. SCHEDULE II - VALUATION AND QUALIFYING ACCOUNTS For the Years Ended (in thousands) Description Balance Beginning of Year Reserves Acquired Charges (Recoveries) to Cost and Expenses Deductions Balance End of Year Year Ended December 31, 2020 Allowance for credit loss reserves (deducted from trade and notes receivable) $ 455 $ 18 $ 230 $ (121 ) $ 582 Year Ended December 31, 2019 Allowance for credit loss reserves (deducted from trade and notes receivable) $ 860 $ — $ (405 ) $ — $ 455 Year Ended December 31, 2018 Allowance for credit loss reserves (deducted from trade and notes receivable) $ 4,039 $ — $ (928 ) $ (2,251 ) $ 860

Nature of Operations and Acco_2

Nature of Operations and Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2020
Accounting Policies [Abstract]
Nature of Operations and Segmentation	Nature of Operations and Segmentation. The consolidated financial statements include the accounts of SEACOR Marine and its consolidated subsidiaries (collectively referred to as the “Company”). The Company provides global marine and support transportation services to offshore oil, natural gas and windfarm facilities worldwide. The Company and its joint ventures operate a diverse fleet of offshore support and specialty vessels that (i) deliver cargo and personnel to offshore installations, (ii) handle anchors and mooring equipment required to tether rigs to the seabed, (iii) tow rigs and assist in placing them on location and moving them between regions, (iv) provide construction, well work-over and decommissioning support and (v) carry and launch equipment used underwater in drilling and well installation, maintenance, inspection and repair. Additionally, the Company’s vessels provide accommodations for technicians and specialists, safety support and emergency response services. The Company’s fleet also includes crew transfer vessels (“CTVs”) used primarily in windfarm operations. Accounting standards require public business enterprises to report information about each of their operating business segments that exceed certain quantitative thresholds or meet certain other reporting requirements. Operating business segments have been defined as a component of an enterprise about which separate financial information is available and is evaluated regularly by the chief operating decision maker in assessing performance. As a result of the announced sale of Windcat Workboats Holdings Ltd (“Windcat Workboats”), the Company’s indirect wholly owned subsidiary, and the CTV business of Windcat Workboats (the “Windcat Workboats CTV Business”) on December 18, 2020, the Company classified the CTV assets of the Windcat Workboats CTV Business as Assets held for sale as of December 31, 2020. Unless the context indicates otherwise, all of the results presented exclude the CTV operations of the Windcat Workboats CTV Business which are classified as Assets held for sale. The Company has identified the following five principal geographic regions as its reporting segments: United States, primarily Gulf of Mexico. As of December 31, 2020, 23 vessels were located in the U.S. Gulf of Mexico, including 17 owned, three leased-in, two joint-ventured and one managed-in. The Company’s vessels in this market support deep-water anchor handling, fast cargo transport, general cargo transport, well intervention, work-over, decommissioning and diving support operations. Africa, primarily West Africa. As of December 31, 2020, 15 vessels were located in West Africa, including 13 owned, one leased-in and one joint-ventured. The Company’s vessels in this area generally support projects for major oil companies, primarily in Angola and Nigeria. Middle East and Asia. As of December 31, 2020, 23 vessels were located in the Middle East and Asia, including 20 owned, two joint-ventured and one managed. The Company’s vessels in this area generally support exploration, personnel transport and seasonal construction activities in Egypt, Israel and Malaysia and countries along the Arabian Gulf and Arabian Sea, such as Saudi Arabia, the United Arab Emirates and Qatar. Latin America. As of December 31, 2020, 38 vessels were located in this region, including eight owned and 30 joint ventured. Of these joint-ventured vessels, (i) 16 are owned by Mantenimiento Express Maritimo, S.A.P.I. de C.V. (“MexMar”), a joint venture company that is 49% owned by SEACOR Marine International LLC (“SMI”), a wholly owned subsidiary of SEACOR Marine, and 51% owned by subsidiaries of Proyectos Globales de Energía y Servicios CME, S.A. de C.V. (“CME”), and (ii) 13 are owned by MEXMAR Offshore International LLC (“MEXMAR Offshore”), a joint venture company that is 49% owned by SMI and 51% owned by a subsidiary of CME. These vessels, consisting of a fleet of FSVs, supply, specialty and liftboat vessels, provide support for exploration and production activities in Mexico, Brazil and Guyana. From time to time, the Company’s vessels also work in Trinidad and Tobago, and Colombia. Europe, primarily North Sea. As of December 31, 2020, the Company had two owned vessels that are were classified in our continuing operations, located in this region, supporting the construction and maintenance of offshore wind turbines as well as supporting oil and gas explorations and production operations in the North Sea. On December 18, 2020, the Company announced the sale of its Windcat Workboats CTV Business (“Windcat Sale”), comprised of 46 CTVs located in Europe providing crew transfer to offshore wind platforms, which closed on January 12, 2021. As a result of the announced sale of the Windcat Workboats CTV Business on December 18, 2020, the Company classified the CTV assets of the Windcat Workboats CTV Business as Assets held for sale as of December 31, 2020
Basis of Consolidation	Basis of Consolidation. The consolidated financial statements include the accounts of SEACOR Marine and its controlled subsidiaries. Control is generally deemed to exist if the Company has greater than 50% of the voting rights of a subsidiary. All significant intercompany accounts and transactions are eliminated in the combination and consolidation. Noncontrolling interests in consolidated subsidiaries are included in the consolidated balance sheets as a separate component of equity. The Company reports consolidated net income (loss) inclusive of both the Company ’ s and the noncontrolling interests' share, as well as the amounts of consolidated net income (loss) attributable to each of the Company and the noncontrolling interests. If a subsidiary is deconsolidated upon a change in control, any retained noncontrolled equity investment in the former controlled subsidiary is measured at fair value and a gain or loss is recognized in net income (loss) based on such fair value. If a subsidiary is consolidated upon a change in control, any previous noncontrolled equity investment in the subsidiary is measured at fair value and a gain or loss is recognized in net income (loss) based on such fair value. The Company employs the equity method of accounting for investments in 50% or less owned companies that it does not control but has the ability to exercise significant influence over the operating and financial policies of the business venture. Significant influence is generally deemed to exist if the Company has between 20% and 50% of the voting rights of a business venture, but may exist when the Company’s ownership percentage is less than 20%. In certain circumstances, the Company may have an economic interest in excess of 50% but may not control and consolidate the business venture. Conversely, the Company may have an economic interest less than 50% but may control and consolidate the business venture. The Company reports its investments in and advances to these business ventures in the accompanying consolidated balance sheets as investments, at equity, and advances to 50% or less owned companies. The Company reports its share of earnings from investments in 50% or less owned companies in the accompanying consolidated statements of loss as equity in earnings (losses) of 50% or less owned companies, net of tax. The Company reports its qualifying investments at cost, less impairment if any, plus or minus observable price changes in orderly transactions for an identical or similar investment of the same issuer for its investments in 50% or less owned companies it does not control or exercise significant influence. These investments in private companies are adjusted for capital distributions and other-than-temporary declines in fair value. Certain reclassifications were made to previously reported amounts in the consolidated financial statements and notes thereto to make them consistent with the current period presentation.
Use of Estimates	Use of Estimates. The preparation of financial statements in conformity with accounting principles generally accepted in the U.S. requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Such estimates include those related to deferred revenues, allowance for credit losses, useful lives of property and equipment, impairments, income tax provisions and certain accrued liabilities. Actual results could differ from estimates and those differences may be material.
Revenue Recognition	Revenue Recognition. The Company contracts with various customers to carry out management services for vessels as agents for and on behalf of ship owners. These services include crew management, technical management, commercial management, insurance arrangements, sale and purchase of vessels, provisions and bunkering. As the manager of the vessels, the Company undertakes to use its best endeavors to provide the agreed management services as agents for and on behalf of the owners in accordance with sound ship management practice and to protect and promote the interest of the owners in all matters relating to the provision of services hereunder. The Company also contracts with various customers to carry out management services regarding engineering for vessel construction and vessel conversions. The vast majority of the ship management agreements span over the length of one to three years and are typically billed on a monthly basis. The Company transfers control of the service to the customer and satisfies its performance obligation over the term of the contract, and therefore recognized revenue over the term of the contract while related costs are expensed as incurred. Revenue that does not meet these criteria is deferred until the criteria is met and such revenue is considered a contract liability. Contract liabilities, which are included in other current liabilities from continuing operations in the accompanying consolidated balance sheets, for the years ended December 31 were as follows (in thousands): 2020 2019 2018 Balance at beginning of year $ 4,755 $ 1,327 $ 10,104 Revenues deferred during the year 2,042 8,134 3,518 Revenues recognized during the year (3,490 ) (4,706 ) (12,295 ) Balance at end of year $ 3,307 $ 4,755 $ 1,327 As of December 31, 2020 the Company deferred revenues of $3.3 million primarily related to $2.0 million of prepaid vessel management fees, $0.8 million related to the time charter of offshore support vessels to customers from which collections were not reasonably assured and $0.5 million of prepaid charter modification and reservation fees. The Company earns revenue primarily from the time charter and bareboat charter of vessels to customers. Since the Company charges customers based upon daily rates of hire, vessel revenues are recognized on a daily basis throughout the contract period. Under a time charter, the Company provides a vessel to a customer and is responsible for all operating expenses, typically excluding fuel. Under a bareboat charter, the Company provides a vessel to a customer and the customer assumes responsibility for all operating expenses and assumes all risks of operation. In the U.S. Gulf of Mexico, time charter durations and rates are typically established in the context of master service agreements that govern the terms and conditions of the charter. From time to time, the Company may also participate in pooling arrangements. In a pooling arrangement, the time charter revenues of certain of the Company’s vessels are shared with the time charter revenues of certain vessels of similar type owned by non-affiliated vessel owners based upon an agreed formula. On January 9, 2019, the only active pooling arrangement was terminated, and three FSV’s were purchased by the Company. Contract or charter durations may range from several days to several years. Charters vary in length from short-term to multi-year periods, many with cancellation clauses and without early termination penalties. As a result of options and frequent renewals, the stated duration of charters may have little correlation with the length of time the vessel is contracted to provide services to a particular customer.
Cash Equivalents	Cash Equivalents. The Company considers all highly liquid investments with an original maturity of three months or less, when purchased, to be cash equivalents. Cash equivalents consist of U.S. treasury securities, money market instruments, time deposits and overnight investments.
Restricted Cash	Restricted Cash. Restricted cash primarily relates to banking facility requirements. For the year ended December 31, cash, cash equivalents and restricted cash from continuing operations consists of: 2020 2019 Cash $ 32,666 $ 81,382 Restricted cash 3,352 3,104 Total $ 36,018 $ 84,486
Trade and Other Receivables	Trade and Other Receivables. Customers are primarily major integrated national and international oil companies, large independent oil and natural gas exploration and production companies, and offshore windfarm operations. Customers are granted credit on a short-term basis and the related credit risks are minimal. Other receivables consist primarily of operating expenses the Company incurs in relation to vessels it manages for other entities, as well as insurance and income tax receivables. The Company routinely reviews its receivables and makes provisions for credit losses; however, those provisions are estimates and actual results may materially differ from those estimates. Trade receivables are deemed uncollectible and are removed from accounts receivable and the allowance for credit losses when collection efforts have been exhausted.
Derivative Instruments	Derivative Instruments. The Company accounts for derivatives through the use of a fair value concept whereby all of the Company’s derivative positions are stated at fair value in the accompanying consolidated balance sheets. Realized and unrealized gains and losses on derivatives not designated as hedges are reported in the accompanying consolidated statements of loss as Derivative gains (losses), net. Realized and unrealized gains and losses on derivatives designated as fair value hedges are recognized as corresponding increases or decreases in the fair value of the underlying hedged item to the extent they are effective, with any ineffective portion reported in the accompanying consolidated statements of loss as Derivative gains (losses), net. Realized and unrealized gains and losses on derivatives designated as cash flow hedges are reported as a component of other comprehensive loss in the accompanying consolidated statements of comprehensive loss to the extent they are effective and reclassified into earnings on the same line item associated with the hedged transaction and in the same period the hedged transaction affects earnings. Any ineffective portions of cash flow hedges are reported in the accompanying consolidated statements of loss as Derivative gains (losses), net. Realized and unrealized gains and losses on derivatives designated as cash flow hedges that are entered into by the Company’s 50% or less owned companies are also reported as a component of the Company’s other comprehensive loss in proportion to the Company’s ownership percentage, with reclassifications and ineffective portions being included in Equity in earnings (losses) of 50% or less owned companies, net of tax, in the accompanying consolidated statements of loss.
Concentrations of Credit Risk	Concentrations of Credit Risk. The Company is exposed to concentrations of credit risk associated with its cash and cash equivalents, restricted cash, construction reserve funds and derivative instruments. The Company minimizes its credit risk relating to these positions by monitoring the financial condition of the financial institutions and counterparties involved and by primarily conducting business with large, well-established financial institutions and diversifying its counterparties. The Company does not currently anticipate nonperformance by any of its significant counterparties. The Company is also exposed to concentrations of credit risk relating to its receivables due from customers described above. The Company does not generally require collateral or other security to support its outstanding receivables. The Company minimizes its credit risk relating to receivables by performing ongoing credit evaluations and, to date, credit losses have not been material.
Inventories	Inventories. Inventories, which consist of fuel and supplies, are stated at the lower of cost (using the first-in, first-out method) or market. The Company records write-downs, as needed, to adjust the carrying amount of inventories to the lower of cost or market. In the year ended December 31 , 2020, 201 9 and 201 8 , t here were no inventory reserves .
Property and Equipment	Property and Equipment. Equipment, stated at cost, is depreciated using the straight-line method over the estimated useful life of the asset to an estimated salvage value. With respect to offshore support vessels, the estimated useful life is typically based upon a newly built vessel being placed into service and represents the point at which it is typically not justifiable for the Company to continue to operate the vessel in the same or similar manner. From time to time, the Company may acquire older vessels that have already exceeded the Company’s useful life policy, in which case the Company depreciates such vessels based on its best estimate of remaining useful life, typically the next regulatory survey or certification date. As of December 31, 2020, the estimated useful life (in years) of each of the Company’s major categories of new offshore support vessels was as follows: Offshore Support Vessels: CTVs 10 All other offshore support vessels (excluding crew transfer) 20 The Company’s property and equipment from continuing operations as of December 31 was as follows (in thousands): Historical Cost (1) Accumulated Depreciation Net Book Value 2020 Offshore support vessels: AHTS ( 2) $ 50,189 $ (31,779 ) $ 18,410 FSV ( 3) 375,747 (104,739 ) 271,008 Supply 238,624 (15,991 ) 222,633 Liftboats 321,751 (117,364 ) 204,387 Crew transfer 3,163 (3,138 ) 25 General machinery and spares 7,746 (7,733 ) 13 Other (4) 15,653 (10,794 ) 4,859 $ 1,012,873 $ (291,538 ) $ 721,335 2019 Offshore support vessels: AHTS ( 2) $ 94,078 $ (73,095 ) $ 20,983 FSV ( 3) 388,460 (101,295 ) 287,165 Supply 44,958 (8,471 ) 36,487 Specialty 14,805 (10,466 ) 4,339 Liftboats 327,028 (93,166 ) 233,862 Crew transfer 5,032 (4,518 ) 514 General machinery and spares 7,650 (7,648 ) 2 Other (4) 17,013 (10,258 ) 6,755 $ 899,024 $ (308,917 ) $ 590,107 (1) Includes property and equipment acquired in business acquisitions at acquisition date fair value, and net of the impact of recognized impairment charges. (2) Anchor Handling Towing (“AHTS”). (3) Fast support vessels (“FSVs”). ( 4 ) Includes land, buildings, leasehold improvements, vehicles and other property and equipment. Depreciation and amortization expense from continuing operations totaled $57.2 million, $57.2 million and $61.4 million in 2020, 2019 and 2018, respectively. Depreciation and amortization from discontinued operations totaled $6.2 million, $ million and $ million in 2020, 2019 and 2018. On December 2, 2019, the Company completed the sale of its North Sea standby business, comprised of 18 emergency response and rescue vehicles (“ERRVs”) with a net book value of $24.3 million. Depreciation and amortization expense totaled $3.5 million and $3.4 million in 2019 and 2018, respectively. Equipment maintenance and repair costs and the costs of routine overhauls, drydockings and inspections performed on vessels and equipment are charged to operating expense as incurred. Expenditures that extend the useful life or improve the marketing and commercial characteristics of vessels, as well as major renewals and improvements to other properties, are capitalized. Certain interest costs incurred during the construction of vessels are capitalized as part of the vessels’ carrying values and are amortized over such vessels estimated useful lives. Capitalized interest totaled $0.7 million, $1.5 million and $2.4 million in 2020, 2019 and 2018, respectively.
Impairment of Long-Lived Assets and Impairment of 50% or Less Owned Companies	Impairment of Long-Lived Assets. The Company performs an impairment analysis of long-lived assets used in operations, including intangible assets, when indicators of impairment are present. These indicators may include a significant decrease in the market price of a long-lived asset or asset group, a significant adverse change in the extent or manner in which a long-lived asset or asset group is being used or in its physical condition, or a current period operating or cash flow loss combined with a history of operating or cash flow losses or a forecast that demonstrates continuing losses associated with the use of a long-lived asset or asset group. If the carrying values of the assets are not recoverable, as determined by their estimated future undiscounted cash flows, the estimated fair value of the assets or asset groups are compared to their current carrying values and impairment charges are recorded if the carrying value exceeds fair value. As a result of the difficult conditions experienced in the offshore oil and natural gas markets beginning in the second half of 2014 and the corresponding reductions in utilization and rates per day worked of its fleet, the Company identified indicators of impairment and recognized impairment charges primarily associated with its AHTS fleet, its liftboat fleet, certain specialty vessels, vessels removed from service and goodwill. When reviewing its fleet for impairment, the Company groups vessels with similar operating and marketing characteristics, including cold-stacked vessels expected to return to active service, into vessel classes. All other vessels, including vessels retired and removed from service, are evaluated for impairment on a vessel by vessel basis. During the year ended December 31, 2020, the Company recorded non-cash impairment charges totaling million. The Company recorded partial impairments ($5.3 million) on the five-company owned liftboat vessels based on outside valuations of its remaining fleet. Estimated fair values for the Company owned vessels were established by independent appraisers based on researched market information, replacement cost information and other data. If market conditions further decline from the depressed utilization and rates per day worked experienced over the last three years, fair values based on future appraisals could decline significantly. In addition, the Company impaired ($7.0 million) on two leased-in liftboat vessels that based on current market environment, were determined that neither of these two leased-in vessels would return to active service during their remaining lease terms. Additionally, one leased-in anchor-handling towing supply (“AHTS”) was impaired ($0.5 million), one specialty vessel was impaired ($1.2 million) and one hull that was included in construction in progress was impaired ($4.8 million). During the year ended December 31, 2019, the Company recorded non-cash impairment charges of $12.0 million, primarily related to four AHTS vessels previously removed from service and adjusted to scrap value, and four fast support vessels (“FSV”), each of which has been adjusted to indicative sales price, and two leased-in vessels (one AHTS and one platform supply vessel “PSV”), adjusted for indicative future cash flows . During the year ended December 31, 2018, the Company recorded non-cash impairment charges of $14.6 million primarily associated with its AHTS fleet (four owned vessels and three leased-in vessels) and one specialty vessel. The Company’s other vessel classes and other individual vessels in active service and cold-stacked status, for which no impairment was deemed necessary, have generally experienced a less severe decline in utilization and rates per day worked based on specific market factors. The market factors include vessels with more general utility to a broad range of customers (e.g., FSVs), vessels required for customers to meet regulatory mandates and operating under multiple year contracts or vessels that service customers outside of the offshore oil and natural gas market (e.g., CTVs). For vessel classes and individual vessels with indicators of impairment but not recently impaired as of December 31, 2020 the Company has estimated that their future undiscounted cash flows exceed their current carrying values. The Company’s estimates of future undiscounted cash flows are highly subjective as utilization and rates per day worked are uncertain, including the timing of an estimated market recovery in the offshore oil and natural gas markets and the timing and cost of reactivating cold-stacked vessels. If market conditions decline further, changes in the Company’s expectations on future cash flows may result in recognizing additional impairment charges related to its long-lived assets in future periods. Impairment of 50% or Less Owned Companies. Investments in 50% or less owned companies are reviewed periodically to assess whether there is an other-than-temporary decline in the carrying value of the investment. In its evaluation, the Company considers, among other items, recent and expected financial performance and returns, impairments recorded by the investee and the capital structure of the investee. When the Company determines the estimated fair value of an investment is below carrying value and the decline is other-than-temporary, the investment is written down to its estimated fair value. Actual results may vary from the Company’s estimates due to the uncertainty regarding projected financial performance, the severity and expected duration of declines in value, and the available liquidity in the capital markets to support the continuing operations of the investee, among other factors. Although the Company believes its assumptions and estimates are reasonable, the investee’s actual performance compared with the estimates could produce different results and lead to additional impairment charges in future periods. No impairment charges of investments in 50% or less owned companies were incurred for the years ended December 31, 2020 and 2019. During the year ended December 31, 2018 the Company recognized impairment charges of $1.2 million net of tax, related to its 50% or less owned companies (see “Note 5. Investments, at Equity, and Advances to 50% or Less Owned Companies”).
Business Combinations	Business Combinations. The Company recognizes 100% of the fair value of assets acquired, liabilities assumed, and noncontrolling interests when the acquisition constitutes a change in control of the acquired entity. Shares issued in consideration for a business combination, contingent consideration arrangements and pre-acquisition loss and gain contingencies are all measured and recorded at their acquisition-date fair value. Subsequent changes to fair value of contingent consideration arrangements are generally reflected in earnings. Acquisition-related transaction costs are expensed as incurred and any changes in an acquirer’s existing income tax valuation allowances and tax uncertainty accruals are recorded as an adjustment to income tax expense. The operating results of entities acquired are included in the accompanying consolidated statements of loss from the date of acquisition (see “Note 3 Business Acquisitions”).
Debt Discount and Issue Costs	Debt Discount and Issue Costs . Debt discounts and costs incurred in connection with the issuance of debt are amortized over the life of the related debt using the effective interest rate method for term loans and straight-line method for revolving credit facilities and are included in interest expense in the accompanying consolidated statements of loss.
Self-insurance Liabilities	Self-insurance Liabilities . The Company maintains marine hull, liability and war risk, general liability, workers compensation and other insurance customary in the industry in which it operates. Both the marine hull and liability policies have annual aggregate deductibles. Marine hull annual aggregate deductibles are accrued as claims are incurred while marine liability annual aggregate deductibles are accrued based on historical loss experience. Exposure to the health benefit plans are limited by maintaining stop-loss and aggregate liability coverage. To the extent that estimated self-insurance losses, including the accrual of annual aggregate deductibles, differ from actual losses realized, the Company’s insurance reserves could differ significantly and may result in either higher or lower insurance expense in future periods.
Income Taxes	Income Taxes . Deferred income tax assets and liabilities have been provided in recognition of the income tax effect attributable to the book and tax basis differences of assets and liabilities reported in the accompanying consolidated financial statements. Deferred tax assets or liabilities are provided using the enacted tax rates expected to apply to taxable income in the periods in which they are expected to be settled or realized. Interest and penalties relating to uncertain tax positions are recognized in interest expense and administrative and general, respectively, in the accompanying consolidated statements of loss. The Company records a valuation allowance to reduce its deferred tax assets if it is more likely than not that some portion or all of the deferred tax assets will not be realized. The Global Intangible Low Taxed Income (“GILTI”) regime effectively imposes a minimum tax on worldwide foreign earnings and subjects U.S. shareholders of controlled foreign corporations (“CFCs”) to current taxation on certain income earned through a CFC. The Company has made the policy election to record any liability, associated with GILTI in the period in which it is incurred. SEACOR Marine was included in the consolidated U.S. federal income tax return of SEACOR Holdings Inc. (“SEACOR Holdings”) through 2016. SEACOR Holdings’ policy for allocation of U.S. federal income taxes required its domestic subsidiaries included in the consolidated U.S. federal income tax return to compute their provision for U.S. federal income taxes on a separate company basis and settle with SEACOR Holdings. In the normal course of business, the Company or SEACOR Holdings may be subject to challenges from tax authorities regarding the amount of taxes due for the Company. These challenges may alter the timing or amount of taxable income or deductions. As part of the calculation of income tax expense, the Company determines whether the benefits of its tax positions are at least more likely than not of being sustained based on the technical merits of the tax position. For tax positions that are more likely than not of being sustained, the Company accrues the largest amount of the tax benefit that is more likely than not of being sustained. Such accruals require management to make estimates and judgments with respect to the ultimate outcome of its tax benefits and actual results could vary materially from these estimates. On June 26, 2020, the Company entered into the Tax Refund Agreement with SEACOR Holdings (see “Note 17. Related Party Transactions”).
Deferred Gains - Vessel Sale-Leaseback Transactions and Financed Vessel Sales	Deferred Gains - Vessel Sale-Leaseback Transactions and Financed Vessel Sales . Prior to the implementation of ASC 842, the Company entered into vessel sale-leaseback transactions with finance companies or provided seller financing on sales of its vessels to third-parties or to 50% or less owned companies. A portion of the gains realized from these transactions was not immediately recognized in income but rather was recorded in the accompanying consolidated balance sheets in deferred gains and other liabilities. In sale-leaseback transactions, gains were deferred to the extent of the present value of future minimum lease payments and were amortized as reductions to rental expense over the applicable lease terms (see “Note 7. Leases”). When the Company determines that future cash inflows do not support future lease cash obligations, the Company records an impairment expense for the amount of the cash flow shortage of all future lease costs, costs to maintain the vessel to the end of the lease term, and costs to return the vessel to its owner, less the amount of any unamortized deferred gains. In financed vessel sales, gains were deferred to the extent that the repayment of purchase notes were dependent on the future operations of the sold vessels and were amortized based on cash received from the buyers. Unamortized deferred gains for four vessels under sale-leaseback agreements were fully recognized in 2019 as an adjustment to the opening balance of Retained Earnings with the implementation of the new leasing standard (see “Note 7. Leases”). Deferred gain activity related to these transactions for the years ended December 31 was as follows (in thousands): 2019 2018 Balance at beginning of year $ 11,026 $ 23,553 Amortization of deferred gains included in operating expenses as reduction to rental expense — (8,037 ) Reclass of gain to Retained Earnings (11,026 ) — Recognition of deferred gains included in losses on asset dispositions and impairments, net — (4,490 ) Balance at end of year $ — $ 11,026 Deferred Gains - Vessel Sales to the Company’s 50% or Less Owned Companies. A portion of the gains realized from non-financed sales of the Company’s vessels to its 50% or less owned companies has been deferred and recorded in the accompanying consolidated balance sheets in deferred gains and other liabilities. In most instances, the sale of a Company vessel to a 50% or less owned company is considered a sale of a business in which the Company relinquishes control to its 50% or less owned company resulting in gain recognition; however, the Company defers gains to the extent of any uncalled capital commitment it has with the 50% or less owned company. The Company no 2019 2018 Balance at beginning of year $ 793 $ 1,453 Amortization of deferred gains included in losses on asset dispositions and impairments, net — (25 ) Other (793 ) (635 ) Balance at end of year $ — $ 793
Foreign Currency Translation	Foreign Currency Translation. The assets, liabilities and results of operations of certain consolidated subsidiaries are measured using their functional currency, which is the currency of the primary foreign economic environment in which they operate. Upon consolidating these subsidiaries with the Company, their assets and liabilities are translated to U.S. dollars at currency exchange rates as of the consolidated balance sheet dates and their revenues and expenses are translated at the weighted average currency exchange rates during the applicable reporting periods. Translation adjustments resulting from the process of translating these subsidiaries’ financial statements are reported in other comprehensive loss in the accompanying consolidated statements of comprehensive loss. Foreign Currency Transactions. Certain consolidated subsidiaries enter into transactions denominated in currencies other than their functional currency. Gains and losses resulting from changes in currency exchange rates between the functional currency and the currency in which a transaction is denominated are included in foreign currency losses, net in the accompanying consolidated statements of loss in the period in which the currency exchange rates change.
Accumulated Other Comprehensive (Loss) Income	Accumulated Other Comprehensive (Loss) Income. The components of accumulated other comprehensive loss were as follows (in thousands): SEACOR Marine Holdings Inc. Stockholders' Equity Noncontrolling Interests Foreign Currency Translation Adjustments Derivative Gains (Losses) on Cash Flow Hedges, net Total Foreign Currency Translation Adjustments Derivative Gains (Losses) on Cash Flow Hedges, net Other Comprehensive (Loss) Income Year Ended December 31, 2017 $ (13,195 ) $ 702 $ (12,493 ) $ (1,357 ) $ 1 $ (881 ) Other comprehensive loss (2,277 ) (1,972 ) (4,249 ) (88 ) (12 ) $ (4,349 ) Income tax (expense) — (46 ) (46 ) — — (46 ) Year Ended December 31, 2018 (15,472 ) (1,316 ) (16,788 ) (1,445 ) (11 ) $ (4,395 ) Other comprehensive income 20,157 (1,994 ) 18,163 — — $ 18,163 Income tax benefi — 173 173 — — 173 Year Ended December 31, 2019 4,685 (3,137 ) 1,548 (1,445 ) (11 ) $ 18,336 Other comprehensive income 2,112 (870) 1,242 — — $ 1,242 Income tax benefit (expense) — — — — — — Year Ended December 31, 2020 $ 6,797 $ (4,007 ) $ 2,790 $ (1,445 ) $ (11 ) $ 1,242
Loss Per Share	Loss Per Share. Basic loss per common share of the Company is computed based on the weighted average number of common shares issued and outstanding during the relevant periods. Diluted loss per common share of the Company is computed based on the weighted average number of common shares issued and outstanding plus the effect of potentially dilutive securities through the application of the treasury stock and if-converted methods. Dilutive securities for this purpose assume restricted stock grants have vested, common shares have been issued pursuant to the exercise of outstanding stock options and common shares have been issued pursuant to the conversion of the Convertible Senior Notes. For the years ended December 31, 2020, 2019 and 2018, diluted loss per common share of the Company excluded 1,488,292 shares, 1,826,966 shares, and 2,183,708 shares, respectively, issuable upon the conversion of the Convertible Senior Notes as the effect of their inclusion in the computation would be anti-dilutive. In addition, for the years ended December 31, 2020, 2019 and 2018, diluted loss per common share of the Company excluded 436,714 shares, 303,609 shares and 192,346 shares, respectively, of restricted stock and 1,120,541, 913,569 and 805,566 outstanding stock options as the effect of their inclusion in the computation would be anti-dilutive. In 2020 and 2019, the Company issued 149,200 and 109,600 performance share awards, of which 240,800 were still outstanding as of December 31, 2020. These performance share awards are not considered outstanding until such time as they would be probable of being exercised, therefore they were not included in the computation of earnings (loss) per share.
Recently Adopted Accounting Standards	Recently Adopted Accounting Standards. On May 28, 2014, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2014-09, “Revenue from Contracts with Customers (Topic 606)” to clarify the principles for recognizing revenue and to develop a common revenue standard and disclosure requirements. The standard supersedes previous revenue recognition requirements and industry-specific guidance. Under the standard, revenue is recognized when a customer obtains control of promised goods or services in an amount that reflects the consideration the entity expects to receive in exchange for those goods or services. The Company adopted this standard on January 1, 2018 using the modified retrospective approach by recognizing the cumulative effect of initially applying the standard as an adjustment to the opening balance of retained earnings. The Company implemented the necessary changes to its business processes, systems and controls to support recognition and disclosure of this ASU upon adoption. The Company’s revenues are primarily based on leases or rental agreements with customers which are not addressed in the standard. As a result, the adoption of the accounting standard did not have a material effect on the Company’s consolidated financial position, results of operations or cash flows, but did result in increased disclosures related to revenue recognition policies. On February 25, 2016, the FASB issued a comprehensive new leasing standard meant to improve transparency and comparability among companies by requiring lessees to recognize a lease liability and a corresponding lease asset for virtually all lease contracts. It also requires additional disclosures about leasing arrangements. The Company adopted the new standard on January 1, 2019 and applied the transition provisions of the new standard at its adoption date with recognition of a cumulative-effect adjustment to the opening balance of retained earnings. The adoption of the new standard had a material impact on the Company’s consolidated financial position, results of operations and cash flows. The adjustment to the Company’s balance sheet on January 1, 2019 included the addition of $33.7 million of right-of-use assets, $31.9 million in lease liability, and a cumulative-effect adjustment to the opening balance of retained earnings of $1.7 million for certain of its equipment, office and land leases. In addition, unamortized deferred gains for four vessels leased under sale-leaseback arrangements were fully recognized as an adjustment to the opening balance of retained earnings of $8.7 million, net of tax, ($11.0 million deferred gains net of $2.3 million deferred taxes). On October 24, 2016, the FASB issued a new accounting standard, which requires companies to account for the income tax effects of intercompany sales and transfers of assets other than inventory. The Company adopted the new standard on January 1, 2018, resulting in a reduction of $12.1 million to the Company’s opening retained earnings. On August 28, 2018, the FASB issued ASU No. 2018-13, Fair Value Measurement (Topic 820) On August 29, 2018, the FASB issued ASU No. 2018-15, Intangibles-Goodwill and Other-Internal-Use Software (Subtopic 350-40) On June 30, 2016, the FASB issued ASU No. 2016-13, Financial Instruments-Credit Losses (Topic 326). This ASU represents a significant change in the Accounting for Credit Losses. The ASU introduced a new accounting model, the Current Expected Credit Losses model (CECL), which required earlier recognition of credit losses and additional disclosures related to credit risk. The CECL model utilizes a lifetime expected credit loss measurement objective for the recognition of credit losses for loans and other receivables at the time the financial asset is originated or acquired. The expected credit losses are adjusted each period for changes in expected lifetime credit losses. This model replaced the multiple existing impairment models in prior U.S. GAAP, which generally required that a loss be incurred before it is recognized. The standard applies to financial assets arising from revenue transactions such as contract assets and accounts receivables. Management implemented the new standard in 2020 and it did not have a material impact on the consolidated financial statements .

Nature of Operations and Acco_3

Nature of Operations and Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2020
Nature Of Operation And Accounting Policies [Abstract]
Schedule of Deferred Revenues	Revenue that does not meet these criteria is deferred until the criteria is met and such revenue is considered a contract liability. Contract liabilities, which are included in other current liabilities from continuing operations in the accompanying consolidated balance sheets, for the years ended December 31 were as follows (in thousands): 2020 2019 2018 Balance at beginning of year $ 4,755 $ 1,327 $ 10,104 Revenues deferred during the year 2,042 8,134 3,518 Revenues recognized during the year (3,490 ) (4,706 ) (12,295 ) Balance at end of year $ 3,307 $ 4,755 $ 1,327
Schedule Of Cash Cash Equivalents And Restricted Cash From Continuing Operations	For the year ended December 31, cash, cash equivalents and restricted cash from continuing operations consists of: 2020 2019 Cash $ 32,666 $ 81,382 Restricted cash 3,352 3,104 Total $ 36,018 $ 84,486
Schedule of Property and Equipment Useful Life	As of December 31, 2020, the estimated useful life (in years) of each of the Company’s major categories of new offshore support vessels was as follows: Offshore Support Vessels: CTVs 10 All other offshore support vessels (excluding crew transfer) 20
Summary of Property and Equipment from Continuing Operations	The Company’s property and equipment from continuing operations as of December 31 was as follows (in thousands): Historical Cost (1) Accumulated Depreciation Net Book Value 2020 Offshore support vessels: AHTS ( 2) $ 50,189 $ (31,779 ) $ 18,410 FSV ( 3) 375,747 (104,739 ) 271,008 Supply 238,624 (15,991 ) 222,633 Liftboats 321,751 (117,364 ) 204,387 Crew transfer 3,163 (3,138 ) 25 General machinery and spares 7,746 (7,733 ) 13 Other (4) 15,653 (10,794 ) 4,859 $ 1,012,873 $ (291,538 ) $ 721,335 2019 Offshore support vessels: AHTS ( 2) $ 94,078 $ (73,095 ) $ 20,983 FSV ( 3) 388,460 (101,295 ) 287,165 Supply 44,958 (8,471 ) 36,487 Specialty 14,805 (10,466 ) 4,339 Liftboats 327,028 (93,166 ) 233,862 Crew transfer 5,032 (4,518 ) 514 General machinery and spares 7,650 (7,648 ) 2 Other (4) 17,013 (10,258 ) 6,755 $ 899,024 $ (308,917 ) $ 590,107 (1) Includes property and equipment acquired in business acquisitions at acquisition date fair value, and net of the impact of recognized impairment charges. (2) Anchor Handling Towing (“AHTS”). (3) Fast support vessels (“FSVs”). ( 4 ) Includes land, buildings, leasehold improvements, vehicles and other property and equipment.
Schedule Of Deferred Gain Activity	Deferred gain activity related to these transactions for the years ended December 31 was as follows (in thousands): 2019 2018 Balance at beginning of year $ 11,026 $ 23,553 Amortization of deferred gains included in operating expenses as reduction to rental expense — (8,037 ) Reclass of gain to Retained Earnings (11,026 ) — Recognition of deferred gains included in losses on asset dispositions and impairments, net — (4,490 ) Balance at end of year $ — $ 11,026 2019 2018 Balance at beginning of year $ 793 $ 1,453 Amortization of deferred gains included in losses on asset dispositions and impairments, net — (25 ) Other (793 ) (635 ) Balance at end of year $ — $ 793
Schedule of Accumulated Other Comprehensive (Loss) Income	Accumulated Other Comprehensive (Loss) Income. The components of accumulated other comprehensive loss were as follows (in thousands): SEACOR Marine Holdings Inc. Stockholders' Equity Noncontrolling Interests Foreign Currency Translation Adjustments Derivative Gains (Losses) on Cash Flow Hedges, net Total Foreign Currency Translation Adjustments Derivative Gains (Losses) on Cash Flow Hedges, net Other Comprehensive (Loss) Income Year Ended December 31, 2017 $ (13,195 ) $ 702 $ (12,493 ) $ (1,357 ) $ 1 $ (881 ) Other comprehensive loss (2,277 ) (1,972 ) (4,249 ) (88 ) (12 ) $ (4,349 ) Income tax (expense) — (46 ) (46 ) — — (46 ) Year Ended December 31, 2018 (15,472 ) (1,316 ) (16,788 ) (1,445 ) (11 ) $ (4,395 ) Other comprehensive income 20,157 (1,994 ) 18,163 — — $ 18,163 Income tax benefi — 173 173 — — 173 Year Ended December 31, 2019 4,685 (3,137 ) 1,548 (1,445 ) (11 ) $ 18,336 Other comprehensive income 2,112 (870) 1,242 — — $ 1,242 Income tax benefit (expense) — — — — — — Year Ended December 31, 2020 $ 6,797 $ (4,007 ) $ 2,790 $ (1,445 ) $ (11 ) $ 1,242

Transformation, Facility Rest_2

Transformation, Facility Restructuring and Severance Charges (Tables)	12 Months Ended
	Dec. 31, 2020
Restructuring And Related Activities [Abstract]
Schedule of Components of Restructuring Charges	The components of restructuring charges for the years ended December 31, 2020 and 2019, were as follows (in thousands): December 31, 2020 United States (primarily Gulf of Mexico) Africa (primarily West Africa) Middle East and Asia Latin America Europe (primarily North Sea) Total Transformation Plan Severance Charges $ 275 $ — $ 665 $ — $ 185 $ 1,125 Other Charges 31 — 31 — — 62 Total Charges $ 306 — $ 696 — $ 185 $ 1,187 December 31, 2019 United States (primarily Gulf of Mexico) Africa (primarily West Africa) Middle East and Asia Latin America Europe (primarily North Sea) Total Transformation Plan Severance Charges $ 2,995 $ — $ 184 $ — $ 200 $ 3,379 Other Charges 307 — 31 — — 339 Total Charges $ 3,302 — $ 215 — $ 200 $ 3,718

Business Acquisitions (Tables)

Business Acquisitions (Tables)	12 Months Ended
	Dec. 31, 2020
Business Combinations [Abstract]
Summary of Purchase Price Allocation of Acquired Assets	The allocation of the purchase price for the Company’s acquired assets for the six months ended June 30 was as follows (in thousands): Assets Acquired (In Thousands): June 30, 2020 Current Assets 7,700 Fixed Assets 142,282 Current Liabilities (23,929 ) Book Value of Debt Acquired (100,759 ) Discount on Debt Acquired 25,190 Fair Value of Debt Acquired (75,569 ) Total Cost Basis for Purchase 50,484 Purchase Price $ (28,150 ) Acquisition costs (112 ) Equity Investment In SEACOR Offshore Delta (f/k/a SEACOSCO) (22,222 ) (50,484 )

Equipment Acquisitions and Di_2

Equipment Acquisitions and Dispositions (Tables)	12 Months Ended
	Dec. 31, 2020
Property Plant And Equipment [Abstract]
Schedule of Vessel Acquired and Disposed	2020 (1) 2019 (2) 2018 (3) FSV — 2 6 Supply 4 2 5 Liftboat — — — 4 4 11 (1) Excludes three CTVs as assets held for sale and seven PSVs acquired as part of the SEACOSCO Acquisition (See “Note 3. Business Acquisitions”). (2) Ex cludes two CTVs as assets held for sale. ( 3 ) Ex 2020 (1) 2019 2018 ( 2 ) AHTS 2 1 1 FSV 4 5 9 Supply 1 5 — CTV — — — Liftboats 1 3 2 Specialty 2 — — 10 14 12 (1) Excludes three (2) Excludes one CTV from assets held for sale.

Investments, at Equity, and A_2

Investments, at Equity, and Advances to 50% or Less Owned Companies (Tables)	12 Months Ended
	Dec. 31, 2020
Schedule Of Investments [Abstract]
Equity Method Investments	Investments, at equity, and advances to 50% or less owned companies as of December 31 were as follows (in thousands): Ownership 2020 2019 MexMar 49.0 % $ 50,037 $ 54,249 SEACOSCO ( 1) 50.0 % — 37,480 OSV Partners ( 2) 30.4 % 9,094 10,668 SEACOR Marlin 49.0 % 7,979 7,929 MEXMAR Offshore ( 3) 49.0 % 1,960 — Offshore Vessel Holdings 49.0 % 2,388 7,905 Other 20.0% — 50.0% 3,850 2,600 $ 75,308 $ 120,831 (1) The Company acquired the remaining 50% of the SEACOSCO Joint Venture that it did not own on June 30, 2020. (2) The Company owns 66.7 % of the General Partner and 29.7 % of the limited Partner . (3) This Joint Venture holds the investment in UP Offshore . Combined Condensed Financial Information of Other Investees. Summarized financial information of the Company’s other investees, at equity, as of and for the years ended December 31 was as follows (in thousands): 2020 2019 Current assets $ 109,687 $ 106,051 Noncurrent assets 259,424 607,541 Current liabilities 109,074 104,423 Noncurrent liabilities 115,626 331,357 2020 2019 2018 Operating Revenues $ 160,781 $ 136,690 $ 105,163 Costs and Expenses: Operating and administrative 142,228 116,517 75,529 Depreciation 27,044 27,412 25,359 169,272 143,929 100,888 Loss on Asset Dispositions and Impairments, Net — (166 ) (262 ) Operating (Loss) Income $ (8,491 ) $ (7,405 ) $ 4,013 Net Loss $ (18,229 ) $ (36,816 ) $ (14,861 )

Leases (Tables)

Leases (Tables)	12 Months Ended
	Dec. 31, 2020
Leases [Abstract]
Summary of Future Minimum Payments For Leases	As of December 31, 2020, future minimum payments for leases for the years ended December 31 were as follows (in thousands): Operating Leases Finance Leases 2021 $ 7,855 $ 42 2022 639 39 2023 628 39 2024 559 36 2025 539 — Years subsequent to 2025 4,215 — 14,435 156 Interest component (3,060 ) (15 ) 11,375 141 Current portion of long-term operating lease liabilities (7,030 ) (36 ) Long-term operating lease liabilities $ 4,345 $ 105
Summary of Components of Leases Expense	For the years ended December 31, the components of lease expense were as follows (in thousands): 2020 2019 Operating lease expense (1) $ 6,205 $ 13,442 Finance lease cost: Amortization of finance lease asset (1) 11 — Interest on lease liabilities (2) 1 — Short-term lease costs (1) 1,320 2,398 $ 7,537 $ 15,840 (1) Included in selling, general and administrative expenses and amortization costs in the consolidated statements of loss. (2) Included in interest expense in the consolidated statements of loss.
Summary of Supplemental Cash Flow Information Related to Leases	For the year ended December 31, 2020, supplemental cashflow information related to leases were as follows (in thousands): 2020 Operating cash flows from operating leases $ 14,785 Right-of-use assets obtained for operating lease liabilities 1,706 Right-of-use assets obtained for finance lease liabilities 140
Summary of Other Information Related to Leases	For the year ended December 31, 2020, other information related to leases were as follows: 2020 Weighted average remaining lease term, in years - operating leases 7.6 Weighted average remaining lease term, in years - finance leases 4.2 Weighted average discount rate - operating leases 4.7 % Weighted average discount - finance leases 5.3 %

Long-term Debt (Tables)

Long-term Debt (Tables)	12 Months Ended
	Dec. 31, 2020
Debt Disclosure [Abstract]
Schedule of Long-term Debt Obligations	The Company’s long-term debt obligations as of December 31 were as follows (in thousands): December 31,2020 December 31, 2019 Recourse Long-term debt ( 1) Convertible Senior Notes $ 125,000 $ 125,000 SEACOR Marine Foreign Holdings Credit Facility 100,750 113,750 Sea-Cat Crewzer III Term Loan Facility 21,653 24,128 SEACOR Offshore Delta (f/k/a SEACOSCO) Acquisition Debt 19,705 — SEACOR Delta (f/k/a SEACOSCO) Shipyard Financing ( 2) 95,317 — SEACOR Alpine Shipyard Financing ( 3) 31,103 10,534 SEACOR 88/888 Term Loan 5,500 5,500 BNDES Equipment Construction Finance Notes - 3,332 Total recourse Long-term debt 399,028 282,244 Non-recourse Long-term debt ( 4) Falcon Global USA Term Loan Facility 102,349 102,349 Falcon Global USA Revolver 15,000 15,000 SEACOR 88/888 Term Loan 5,500 5,500 Total non-recourse Long-term debt 122,849 122,849 Total principal due for long-term debt 521,877 405,093 Current portion due within one year (32,377 ) (17,802 ) Unamortized debt discount (44,864 ) (26,343 ) Deferred financing costs (4,126 ) (5,234 ) Long-term debt, less current portion $ 440,510 $ 355,714 Long-Term Debt included in current liabilities associated with assets held for sale - Windcat Workboats Facilities $ 27,626 $ 24,537 (1) Recourse debt represents debt issued by SEACOR Marine and/or its subsidiaries and guaranteed by SEACOR Marine as defined in the relevant debt agreements. (2) SEACOR Delta Shipyard Financing includes vessel financing on the eight vessels acquired in the SEACOSCO Acquisition (see “Note 3. Business Acquisitions ”). (3) SEACOR Alpine Shipyard Financing includes vessel financing on the SEACOR Alps, the SEACOR Andes and the SEACOR Atlas vessels. (4) Non-recourse debt represents debt issued by the Company’s Consolidated Subsidiaries with no recourse to SEACOR Marine or its other non-debtor subsidiaries, other than certain limited support obligations as defined in the respective debt agreements, which in aggregate are not considered to be material to the Company’s business and financial condition.
Schedule of Long-term Debt Maturities	The Company’s contractual long-term debt maturities from continuing operations for the years ended December 31 were as follows (in thousands): 2021 $ 32,377 2022 38,484 2023 244,983 2024 134,523 2025 11,365 Years subsequent to 2025 60,145 $ 521,877

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Schedule of Income before Income Tax, Domestic and Foreign	Loss before income tax benefit and equity in earnings (losses) of 50% or less owned companies derived from U.S. and foreign companies for the years ended December 31 were as follows (in thousands): 2020 2019 2018 United States $ (83,560 ) $ (71,833 ) $ (72,540 ) Foreign (17,748 ) (23,663 ) (28,675 ) Eliminations 3,201 11,022 8,782 $ (98,107 ) $ (84,474 ) $ (92,433 )
Schedule of Components of Income Tax Expense (Benefit)	The components of income tax expense (benefit) for the years ended December 31 were as follows (in thousands): 2020 2019 2018 Current: Federal $ (30,838 ) $ (6 ) $ 5,987 State 123 (78 ) 3 Foreign 5,533 5,005 3,307 (25,182 ) 4,921 9,297 Deferred: Federal 2,435 (12,594 ) (21,466 ) State (139 ) (224 ) (1,404 ) Foreign (38 ) (72 ) 110 2,258 (12,890 ) (22,760 ) $ (22,924 ) $ (7,969 ) $ (13,463 )
Schedule of Effective Income Tax Rate Reconciliation	The following table reconciles the difference between the statutory federal income tax rate for the Company and the effective income tax rate for the years ended December 31: 2020 2019 2018 Statutory rate (21.0 )% (21.0 )% (21.0 )% U.S. federal income tax law changes (11.8 )% — % — % SEACOR Holdings share awards to Company personnel 0.3 % — % 0.2 % Non-deductible expenses — % — % — % Exclusion of foreign subsidiaries with accumulated losses and withholding tax 7.7 % 7.4 % 9.3 % Noncontrolling interests 1.3 % 1.7 % (1.6 )% State taxes — % (0.3 )% (1.5 )% Return to provision (0.4 )% 2.8 % (0.5 )% Other 0.5 % — % 0.5 % Effective Tax Rate (23.4 )% (9.4 )% (14.6 )%
Schedule of Deferred Tax Assets and Liabilities	The components of net deferred income tax liabilities as of December 31 were as follows (in thousands): 2020 2019 Deferred tax liabilities: Property and equipment $ 58,676 $ 63,827 Investments in 50% or Less Owned Companies 2,925 3,039 Other 4,819 10,612 Total deferred tax liabilities 66,420 77,478 Deferred tax assets: Federal Net Operating Loss Carryforwards 23,061 28,664 Other 10,073 16,561 33,134 45,225 Valuation Allowance (2,536 ) (1,311 ) Total deferred tax assets 30,598 43,914 Net deferred tax liabilities $ 35,822 $ 33,564

Derivative Instruments and He_2

Derivative Instruments and Hedging Strategies (Tables)	12 Months Ended
	Dec. 31, 2020
Derivative Instruments And Hedging Activities Disclosure [Abstract]
Schedule of Fair Value of Derivative Assets and Liabilities From Continuing Operations	The fair values of the Company’s derivative instruments from continuing operations as of December 31 were as follows (in thousands): 2020 2019 Balance Sheet Classification Derivative Asset Derivative Liability Derivative Asset Derivative Liability Derivatives designated as hedging instruments: Interest rate swap agreements (cash flow hedges) Current $ — $ 3,698 $ — $ 2,925 — 3,698 — 2,925 Derivatives not designated as hedging instruments: Forward Exchange Contract Current — 893 — — Conversion option liability on Convertible Senior Notes Long-Term — 2 — 5,205 $ — $ 895 $ — $ 5,205
Effect of Derivative Instruments on Other Comprehensive Income (Loss)	The following tables reflect amounts recorded in Other Comprehensive Income (Loss) (“OCI”) and amounts reclassified from OCI to revenue and expense for the periods indicated: Losses Recognized in OCI on Derivatives (Effective Portion) Derivatives in Cash Flow Hedging Relationships 2020 2019 2018 Interest rate swap contracts $ (2,139 ) $ (1,901 ) $ (1,939 ) Joint venture interest rate swap contracts (156 ) (645 ) (76 ) Losses Reclassified from OCI into Income (Effective Portion) Location of Loss 2020 2019 2018 Interest expense $ 1,425 $ 552 $ 31
Schedule of Gains (Losses) on Derivative Instruments not Designated as Hedging Instruments	The Company recognized gains (losses) on derivative instruments not designated as hedging instruments for the years ended December 31 as follows (in thousands): Derivative gains (losses), net 2020 2019 2018 Conversion option liability on Convertible Senior Notes $ 5,203 $ 71 $ 1,556 Interest rate swap agreements — — 1,298 Forward currency exchange, option and future contracts (893 ) — — $ 4,310 $ 71 $ 2,854

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2020
Fair Value Disclosures [Abstract]
Schedule of Fair Value of Assets and Liabilities Measured on Recurring Basis	The Company’s financial assets and liabilities as of December 31 that are measured at fair value on a recurring basis were as follows (in thousands): Level 1 Level 2 Level 3 (1) 2020 LIABILITIES Derivative instruments (included in other current liabilities) $ — $ 4,591 $ — Conversion Option Liability on Convertible Senior Notes — — 2 2019 ASSETS Construction reserve funds 12,893 — — LIABILITIES Derivative instruments (included in other current liabilities) — 2,925 — Conversion Option Liability on Convertible Senior Notes — — 5,205 (1) For the year ended December 31, 2020, the Company recognized a $5.2 million gain in the fair market valuation of the Conversion Option on the Convertible Senior Notes, as valued by an independent third-party.
Schedule of Estimated Fair Values of Financial Assets and Liabilities	The estimated fair value of the Company’s other financial assets and liabilities as of December 31 were as follows (in thousands): Estimated Fair Value Carrying Amount Level 1 Level 2 Level 3 2020 ASSETS Cash, cash equivalents and restricted cash $ 36,018 $ 36,018 $ — $ — Investments, at cost, in 50% or less owned companies (included in other assets) 132 see below LIABILITIES Long-term debt, including current portion 472,887 — 470,561 — 2019 ASSETS Cash, cash equivalents and restricted cash $ 84,486 $ 84,486 $ — $ — Investments, at cost, in 50% or less owned companies (included in other assets) 132 see below LIABILITIES Long-term debt, including current portion 373,516 — 356,086 —
Schedule of Other Assets and Liabilities Measured at Fair Value	The Company’s non-financial assets and liabilities that were measured at fair value during the years ended December 31 were as follows (in thousands): Level 1 Level 2 Level 3 2020 ASSETS Property and equipment: Liftboats $ — $ 43,005 $ — 2019 ASSETS Property and equipment: AHTS $ — $ 520 $ — FSVs — 1,858 —

Noncontrolling Interests in S_2

Noncontrolling Interests in Subsidiaries (Tables)	12 Months Ended
	Dec. 31, 2020
Noncontrolling Interest [Abstract]
Schedule of Noncontrolling Interests in the Company's Consolidated Subsidiaries	Noncontrolling interests in the Company’s consolidated subsidiaries as of December 31 were as follows (in thousands): Noncontrolling Interests 2020 2019 Falcon Global Holdings — % (1) $ — $ 21,119 Other 1.8 % 319 313 $ 319 $ 21,432 (1) Before March 20, 2020, noncontrolling interest was 28 % .

Share Based Compensation (Table

Share Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2020
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Schedule of Equity Incentive Plan Transactions	The following transactions have occurred in connection with the Company’s share-based compensation under the 2017 Plan and the 2020 Plan during the years ended December 31: 2020 2019 Director Stock Awards Granted 59,900 30,197 Restricted Stock Activity: Outstanding as of the beginning of year 303,609 192,346 Granted 289,452 (1) 245,400 Vested 143,697 131,937 Forfeited 12,650 2,200 Outstanding as of the end of year 436,714 303,609 Stock Option Activity: Outstanding as of the beginning of year 913,569 805,566 Granted 261,972 230,503 Exercised — 113,750 Forfeited 55,000 8,750 Outstanding as of the end of year 1,120,541 913,569 (1) Excludes 240,800 grants of performance-based stock units that are not considered outstanding until such time that they become probable to vest.
Schedule of Restricted Stock Transactions	During the year ended December 31, 2020, the number of shares and the weighted average grant price of restricted stock transactions were as follows: Restricted Stock Number of Shares Weight Average Grant Price Non-Vested as of December 31, 2019 303,609 $ 20.46 Granted 289,452 6.81 Vested 143,697 13.43 Forfeited 12,650 12.30 Non-Vested as of December 31, 2020 436,714 11.60
Schedule of Stock Option Transactions	During the year ended December 31, 2020, the number of shares and the weighted average exercise price on stock option transactions were as follows: Stock Options Number of Shares Weight Average Grant Price Non-Vested as of December 31, 2019 913,569 $ 14.81 Granted 261,972 3.68 Exercised — — Forfeited 55,000 13.43 Non-Vested as of December 31, 2020 1,120,541 12.49 Exercisable as of December 31, 2020 (1) 716,965 13.03 (1) The weighted average remaining contractual term is 8.18 years.

Major Customers and Segment I_2

Major Customers and Segment Information (Tables)	12 Months Ended
	Dec. 31, 2020
Segment Reporting [Abstract]
Schedule of Segment Reporting Information, by Segment	The following tables summarize (in thousands) the operating results and property and equipment of the Company’s reportable segments. Direct vessel profit is the Company’s measure of segment profitability, a key metric in assessing the performance of its fleet. Direct vessel profit is defined as operating revenues less direct operating expenses excluding leased-in equipment expense. The Company utilizes direct vessel profit as its primary financial measure to analyze and compare the operating performance of its individual vessels, fleet categories, regions and combined fleet. United States (primarily Gulf of Mexico) Africa (primarily West Africa) Middle East and Asia Latin America Europe Continuing Operations Total For the year ended December 31, 2020 Operating Revenues: Time charter $ 9,873 $ 35,876 $ 52,052 $ 23,806 $ 11,847 $ 133,454 Bareboat charter 2,910 — — — (55 ) 2,855 Other 2,422 (465 ) 2,157 1,084 330 5,528 15,205 35,411 54,209 24,890 12,122 141,837 Direct Costs and Expenses: Operating: Personnel 10,065 10,552 18,188 6,698 2,845 48,348 Repairs and maintenance 1,655 5,175 5,232 2,131 468 14,661 Drydocking 1,167 2,014 759 329 — 4,269 Insurance and loss reserves 1,774 1,026 1,721 462 780 5,763 Fuel, lubes and supplies 1,172 2,940 2,706 990 320 8,128 Other 373 984 6,891 1,369 359 9,976 16,206 22,691 35,497 11,979 4,772 91,145 Direct Vessel (Loss) Profit $ (1,001 ) $ 12,720 $ 18,712 $ 12,911 $ 7,350 50,692 Other Costs and Expenses: Operating: Leased-in equipment $ 4,272 $ 3,029 $ 170 $ 45 $ 9 7,525 Administrative and general 40,051 Depreciation and amortization $ 21,427 $ 10,833 $ 16,595 $ 5,481 $ 2,831 57,167 104,743 Losses on Asset Dispositions and Impairments, Net (17,588 ) Operating Loss $ (71,639 ) As of December 31, 2020 Property and Equipment: Historical cost $ 257,592 $ 204,079 $ 361,514 $ 130,769 $ 58,919 $ 1,012,873 Accumulated depreciation (134,391 ) (60,535 ) (75,349 ) (13,312 ) (7,951 ) (291,538 ) $ 123,201 $ 143,544 $ 286,165 $ 117,457 $ 50,968 $ 721,335 Total Assets ( 1) $ 164,656 $ 153,399 $ 289,314 $ 179,942 $ 74,495 $ 861,806 (1) Total assets exclude $105.6 million of corporate assets, and $50.2 million of assets held for sale. United States (primarily Gulf of Mexico) Africa (primarily West Africa) Middle East and Asia Latin America Europe Continuing Operations Total For the year ended December 31, 2019 Operating Revenues: Time charter $ 38,955 $ 44,160 $ 54,312 $ 11,460 $ 8,165 $ 157,052 Bareboat charter 1,562 — — 3,569 — 5,131 Other 3,806 1,461 1,669 1,390 3,944 12,270 44,323 45,621 55,981 16,419 12,109 174,453 Direct Costs and Expenses: Operating: Personnel 17,491 13,833 16,698 4,459 3,494 55,975 Repairs and maintenance 7,583 4,701 7,182 1,348 587 21,401 Drydocking 4,594 490 600 161 3 5,848 Insurance and loss reserves 2,370 1,051 1,449 311 441 5,622 Fuel, lubes and supplies 2,936 3,471 2,904 1,056 255 10,622 Other 393 4,354 3,095 1,182 1,031 10,055 35,367 27,900 31,928 8,517 5,811 109,523 Direct Vessel Profit $ 8,956 $ 17,721 $ 24,053 $ 7,902 $ 6,298 64,930 Other Costs and Expenses: Operating: Leased-in equipment $ 10,894 $ 3,090 $ 173 $ 10 $ 1,673 15,840 Administrative and general 39,791 Depreciation and amortization $ 21,947 $ 10,404 $ 16,400 $ 6,205 $ 2,210 57,166 112,797 Losses on Asset Dispositions and Impairments, Net (6,461 ) Operating Loss $ (54,328 ) As of December 31, 2019 Property and Equipment: Historical cost $ 297,392 $ 207,107 $ 292,446 $ 57,534 $ 44,545 $ 899,024 Accumulated depreciation (157,514 ) (57,136 ) (73,039 ) (16,239 ) (4,989 ) (308,917 ) $ 139,878 $ 149,971 $ 219,407 $ 41,295 $ 39,556 $ 590,107 Total Assets ( 1) $ 224,229 $ 161,915 $ 250,890 $ 116,736 $ 64,156 $ 817,926 (1) Total assets exclude $145.5 million of corporate assets, and $45.7 million of assets held-for-sale United States (primarily Gulf of Mexico) Africa (primarily West Africa) Middle East and Asia Latin America Europe Continuing Operations Total For the year ended December 31, 2018 Operating Revenues: Time charter $ 38,802 $ 43,847 $ 50,072 $ 17,343 $ — $ 150,064 Bareboat charter — — — 4,635 — 4,635 Other 14,762 7,661 (887 ) 1,554 1,372 24,462 53,564 51,508 49,185 23,532 1,372 179,161 Direct Costs and Expenses: Operating: Personnel 18,708 16,538 16,806 4,399 2,081 58,532 Repairs and maintenance 5,152 6,330 11,172 1,011 720 24,385 Drydocking 1,957 2,085 1,362 128 2,260 7,792 Insurance and loss reserves 2,922 1,096 1,371 495 86 5,970 Fuel, lubes and supplies 3,568 3,826 4,027 1,225 258 12,904 Other 393 4,313 3,980 1,130 188 10,004 32,700 34,188 38,718 8,388 5,593 119,587 Direct Vessel Profit (Loss) $ 20,864 $ 17,320 $ 10,467 $ 15,144 $ (4,221 ) 59,574 Other Costs and Expenses: Operating: Leased-in equipment $ 8,240 $ 4,281 $ 224 $ 5 $ 214 12,964 Administrative and general 41,616 Depreciation and amortization $ 23,227 $ 10,453 $ 18,762 $ 7,908 $ 1,069 61,419 115,999 Losses on Asset Dispositions and Impairments, Net (11,989 ) Operating Loss $ (68,414 ) As of December 31, 2018 Property and Equipment: Historical cost $ 432,336 $ 184,361 $ 306,897 $ 124,177 $ 26 $ 1,047,797 Accumulated depreciation (224,737 ) (55,206 ) (81,378 ) (57,002 ) (17 ) (418,340 ) $ 207,599 $ 129,155 $ 225,519 $ 67,175 $ 9 $ 629,457 Total Assets ( 1) $ 351,748 $ 140,335 $ 260,002 $ 137,983 $ (28,450 ) 861,618 (1) Total assets exclude $153.1 million of corporate assets, and $88.2 million of assets held-for-sale.

Discontinued Operations (Tables

Discontinued Operations (Tables)	12 Months Ended
	Dec. 31, 2020
Discontinued Operations And Disposal Groups [Abstract]
Schedule of Assets Held for Sale	Summarized selected operating result of the Company’s assets held for sale and discontinued operations were as follows for the years ended December 31, (in thousands): 2020 2019 Assets from Discontinued Operations: Current assets $ 10,138 $ 9,603 Net property and equipment 34,580 31,447 Non-current assets 5,517 4,668 50,235 45,718 Liability from Discontinued Operations: Current liabilities $ 2,418 $ 2,060 Long-term liabilities 28,509 25,480 $ 30,927 $ 27,540 Windcat Workboats Boston Putford Offshore Safety 2020 2019 2020 2019 Operating Revenues: Time charter $ 29,383 $ 25,249 $ — $ 41,214 Other revenue 2,305 1,790 — 45 31,688 27,039 — 41,259 Costs and Expenses: Operating 17,334 14,202 — 33,836 Direct Vessel Profit 14,354 12,837 — 7,423 General and Administrative Expenses 5,516 4,935 — 4,207 Lease Expense 628 318 — 60 Depreciation 6,166 6,846 — 3,504 Gains on Asset Dispositions and Impairments, Net — 1,064 — 91 Operating Income (Loss) 2,044 1,802 — (257 ) Other Income (Expense) Interest income 59 56 — 11 Interest expense (1,115 ) (1,100 ) — (210 ) Foreign currency translation (loss) gain (750 ) 880 — (75 ) Other, net 19 — — — (1,787 ) (164 ) — (274 ) Operating Income (Loss) Before Equity Earnings of 50% or Less Owned Companies, Net of Tax 257 1,638 — (531 ) Income Tax (Benefit) Expense (86 ) 57 — (2 ) Operating Income (Loss) Before Equity Earnings of 50% or Less Owned Companies 343 1,581 — (529 ) Equity in Earnings of 50% or Less Owned Companies, Net of Tax 21 155 — 168 Net Income (Loss) from Discontinued Operations $ 364 $ 1,736 $ — $ (361 )

Quarterly Financial Informati_2

Quarterly Financial Information (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2020
Quarterly Financial Information Disclosure [Abstract]
Selected Financial Information for Interim Quarterly Periods	Three Months Ended Dec. 31, Sept. 30, June 30, March 31, 2020 Operating Revenues $ 36,044 $ 36,201 $ 33,925 $ 35,667 Operating Loss (16,915 ) (13,179 ) (17,824 ) (23,721 ) Net (Loss) Income: Continuing Operations (38,898 ) (19,842 ) (6,668 ) (17,938 ) Discontinued Operations 51 1,765 602 (2,054 ) $ (38,847 ) $ (18,077 ) $ (6,066 ) $ (19,992 ) Net Loss attributable to SEACOR Marine Holdings Inc: $ (38,816 ) $ (18,081 ) $ (6,073 ) $ (15,945 ) Basic and Diluted (Loss) Income Per Common Share of SEACOR Marine Holdings Inc. Continuing Operations $ (1.54 ) $ (0.79 ) $ (0.26 ) $ (0.58 ) Discontinued Operations $ — $ 0.07 $ 0.02 $ (0.08 ) $ (1.54 ) $ (0.72 ) $ (0.24 ) $ (0.66 ) 2019 Operating Revenues $ 42,478 $ 46,996 $ 45,014 $ 39,965 Operating Loss (10,555 ) (5,566 ) (18,591 ) (19,616 ) Net (Loss) Income: Continuing Operations (19,439 ) (12,586 ) (31,632 ) (27,307 ) Discontinued Operations (2,479 ) (5,654 ) 1,368 (966 ) $ (21,918 ) $ (18,240 ) $ (30,264 ) $ (28,273 ) Net Loss attributable to SEACOR Marine Holdings Inc: $ (20,455 ) $ (18,444 ) $ (28,389 ) $ (25,549 ) Basic and Diluted (Loss) Income Per Common Share of SEACOR Marine Holdings Inc. Continuing Operations $ (0.76 ) $ (0.54 ) $ (1.27 ) $ (1.07 ) Discontinued Operations $ (0.10 ) $ (0.24 ) $ 0.06 $ (0.04 ) $ (0.86 ) $ (0.78 ) $ (1.21 ) $ (1.11 ) 121

Schedule II - Valuation and Q_2

Schedule II - Valuation and Qualifying Accounts (Tables)	12 Months Ended
	Dec. 31, 2020
Valuation And Qualifying Accounts [Abstract]
Schedule of Valuation and Qualifying Accounts	Description Balance Beginning of Year Reserves Acquired Charges (Recoveries) to Cost and Expenses Deductions Balance End of Year Year Ended December 31, 2020 Allowance for credit loss reserves (deducted from trade and notes receivable) $ 455 $ 18 $ 230 $ (121 ) $ 582 Year Ended December 31, 2019 Allowance for credit loss reserves (deducted from trade and notes receivable) $ 860 $ — $ (405 ) $ — $ 455 Year Ended December 31, 2018 Allowance for credit loss reserves (deducted from trade and notes receivable) $ 4,039 $ — $ (928 ) $ (2,251 ) $ 860

Nature of Operations and Acco_4

Nature of Operations and Accounting Policies - Additional Information (Details)		12 Months Ended
		Dec. 31, 2020USD ($)SegmentVesselshares	Dec. 31, 2019USD ($)shares	Dec. 31, 2018USD ($)shares	Dec. 02, 2019USD ($)	Jan. 01, 2019USD ($)	Dec. 20, 2018	Jan. 01, 2018USD ($)	Dec. 31, 2017USD ($)
Nature Of Operations And Accounting Policies [Line Items]
Number of reportable segments | Segment		5
Equity method investment, ownership percentage							49.00%
Contract with customer, liability		$ 3,307,000	$ 4,755,000	$ 1,327,000					$ 10,104,000
Contract with customer liability current		4,452,000	5,296,000
Inventory reserves		0	0	0
Net book value		721,335,000	590,107,000	629,457,000
Capitalized interest costs, including allowance for funds used during construction, total		700,000	1,500,000	2,400,000
Impairment of long-lived assets held-for-use		18,800,000	12,000,000	14,600,000
Partial impairment of right to use assets		5,300,000
Equity method investment, other than temporary impairment		$ 0	0	$ 1,200,000
Deferred gain net			$ 0
Incremental common shares attributable to conversion of debt securities, total | shares		1,488,292	1,826,966	2,183,708
Right-of-Use Asset - Operating Leases		$ 7,134,000	$ 16,537,000
Operating Lease, Liability		11,375,000
Cumulative effect on retained earnings, net of tax		(51,839,000)	27,076,000
Deferred taxes		$ 66,420,000	$ 77,478,000
Change in Accounting Principle for Unamortized Deferred Gains
Nature Of Operations And Accounting Policies [Line Items]
Deferred gain net						$ 11,000
Deferred taxes						2,300
Accounting Standards Update 2014-09
Nature Of Operations And Accounting Policies [Line Items]
Change in accounting principle, accounting standards update, adopted [true false]		true
Change in accounting principle, accounting standards update, adoption date		Jan. 1, 2018
Change in accounting principle, accounting standards update, immaterial effect [true false]		true
Accounting Standards Update 2016-02
Nature Of Operations And Accounting Policies [Line Items]
Change in accounting principle, accounting standards update, adopted [true false]		true
Change in accounting principle, accounting standards update, adoption date		Jan. 1, 2019
Change in accounting principle, accounting standards update, immaterial effect [true false]		false
Right-of-Use Asset - Operating Leases						33,700,000
Operating Lease, Liability						31,900,000
Accounting Standards Update 2016-02 | Cumulative Effect, Period of Adoption, Adjustment | Change in Accounting Principle for Equipment, Office and Land Leases
Nature Of Operations And Accounting Policies [Line Items]
Cumulative effect on retained earnings, net of tax						1,700,000
Accounting Standards Update 2016-02 | Cumulative Effect, Period of Adoption, Adjustment | Change in Accounting Principle for Unamortized Deferred Gains
Nature Of Operations And Accounting Policies [Line Items]
Cumulative effect on retained earnings, net of tax						$ 8,700,000
Accounting Standards Update 2019-12
Nature Of Operations And Accounting Policies [Line Items]
Change in accounting principle, accounting standards update, adopted [true false]		true
Change in accounting principle, accounting standards update, adoption date		Jan. 1, 2018
Accounting Standards Update 2019-12 | Cumulative Effect, Period of Adoption, Adjustment
Nature Of Operations And Accounting Policies [Line Items]
Cumulative effect on retained earnings, net of tax								$ 12,100,000
Performance Share Awards
Nature Of Operations And Accounting Policies [Line Items]
Number of shares issued | shares		149,200	109,600
Number of shares outstanding | shares		240,800
Restricted Stock
Nature Of Operations And Accounting Policies [Line Items]
Antidilutive securities excluded from computation of earnings per share, amount | shares		436,714	303,609	192,346
Employee Stock Option
Nature Of Operations And Accounting Policies [Line Items]
Antidilutive securities excluded from computation of earnings per share, amount | shares		1,120,541	913,569	805,566
Continuing Operations
Nature Of Operations And Accounting Policies [Line Items]
Depreciation, total		$ 57,200,000	$ 57,200,000	$ 61,400,000
Discontinued Operations
Nature Of Operations And Accounting Policies [Line Items]
Depreciation, total		6,200,000	$ 6,800,000	7,400,000
Net book value					$ 24,300,000
Prepaid Vessel Management Fees
Nature Of Operations And Accounting Policies [Line Items]
Contract with customer liability current		2,000,000
Prepaid Charter Modification and Reservation Fees [Member]
Nature Of Operations And Accounting Policies [Line Items]
Contract with customer liability current		500,000
Geographic Distribution, Domestic
Nature Of Operations And Accounting Policies [Line Items]
Contract with customer, liability		3,300,000
Geographic Distribution, Foreign
Nature Of Operations And Accounting Policies [Line Items]
Contract with customer, liability		$ 800,000
Minimum
Nature Of Operations And Accounting Policies [Line Items]
Equity method investment, ownership percentage		20.00%
Minimum | SEACOR Marine Foreign Holdings
Nature Of Operations And Accounting Policies [Line Items]
Equity method investment, ownership percentage		50.00%
Maximum
Nature Of Operations And Accounting Policies [Line Items]
Equity method investment, ownership percentage		50.00%	50.00%
Crew Transfer Vessels
Nature Of Operations And Accounting Policies [Line Items]
Net book value		$ 25,000	$ 514,000
ERRVs | Discontinued Operations
Nature Of Operations And Accounting Policies [Line Items]
Depreciation, total			3,500,000	3,400,000
Liftboat Vessels
Nature Of Operations And Accounting Policies [Line Items]
Additional impairment of right-to-use assets		7,000,000
Anchor Handling Towing Supply
Nature Of Operations And Accounting Policies [Line Items]
Additional impairment of right-to-use assets		500,000
Specialty Vessel
Nature Of Operations And Accounting Policies [Line Items]
Additional impairment of right-to-use assets		1,200,000
Vessel Under Construction
Nature Of Operations And Accounting Policies [Line Items]
Additional impairment of right-to-use assets		$ 4,800,000
CME
Nature Of Operations And Accounting Policies [Line Items]
Noncontrolling interest, ownership percentage by noncontrolling owners		51.00%
MexMar
Nature Of Operations And Accounting Policies [Line Items]
Number of vessels owned | Vessel		16
Equity method investment, ownership percentage		49.00%
SMI
Nature Of Operations And Accounting Policies [Line Items]
Equity method investment, ownership percentage		49.00%
MEXMAR Offshore
Nature Of Operations And Accounting Policies [Line Items]
Number of vessels owned | Vessel		13
Equity method investment, ownership percentage	[1]	49.00%
UNITED STATES
Nature Of Operations And Accounting Policies [Line Items]
Number of vessels | Vessel		23
Number of vessels owned | Vessel		17
Number of vessels leased-in | Vessel		3
Number of vessels joint ventured | Vessel		2
Number of vessels managed-in | Vessel		1
Net book value		$ 123,201,000	139,878,000	207,599,000
Africa
Nature Of Operations And Accounting Policies [Line Items]
Number of vessels | Vessel		15
Number of vessels owned | Vessel		13
Number of vessels leased-in | Vessel		1
Number of vessels joint ventured | Vessel		1
Net book value		$ 143,544,000	149,971,000	129,155,000
Middle East and Asia
Nature Of Operations And Accounting Policies [Line Items]
Number of vessels | Vessel		23
Number of vessels owned | Vessel		20
Number of vessels joint ventured | Vessel		2
Number of vessels managed-in | Vessel		1
Net book value		$ 286,165,000	219,407,000	225,519,000
Latin America
Nature Of Operations And Accounting Policies [Line Items]
Number of vessels | Vessel		38
Number of vessels owned | Vessel		8
Number of vessels joint ventured | Vessel		30
Net book value		$ 117,457,000	41,295,000	67,175,000
Europe
Nature Of Operations And Accounting Policies [Line Items]
Number of vessels owned | Vessel		2
Net book value		$ 50,968,000	$ 39,556,000	$ 9,000
Europe | Crew Transfer Vessels
Nature Of Operations And Accounting Policies [Line Items]
Number of equipment sold upon completion | Vessel		46
[1]	This Joint Venture holds the investment in UP Offshore .

Nature of Operations and Acco_5

Nature of Operations and Accounting Policies - Schedule Of Deferred Revenues (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Nature Of Operation And Accounting Policies [Abstract]
Balance at beginning of year	$ 4,755	$ 1,327	$ 10,104
Revenues deferred during the year	2,042	8,134	3,518
Revenues recognized during the year	(3,490)	(4,706)	(12,295)
Balance at end of year	$ 3,307	$ 4,755	$ 1,327

Nature of Operations and Acco_6

Nature of Operations and Accounting Policies - Schedule Of Cash, Cash Equivalents And Restricted Cash From Continuing Operations (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Nature Of Operation And Accounting Policies [Abstract]
Cash	$ 32,666	$ 81,382
Restricted cash	3,352	3,104
Total	$ 36,018	$ 84,486

Nature of Operations and Acco_7

Nature of Operations and Accounting Policies - Schedule of Property and Equipment Useful Life (Details)	12 Months Ended
	Dec. 31, 2020
CTVs
Property Plant And Equipment [Line Items]
Estimated useful life (Year)	10 years
All Other Offshore Support Vessels
Property Plant And Equipment [Line Items]
Estimated useful life (Year)	20 years

Nature of Operations and Acco_8

Nature of Operations and Accounting Policies - Summary of Property and Equipment from Continuing Operations (Details) - USD ($) $ in Thousands		Dec. 31, 2020		Dec. 31, 2019		Dec. 31, 2018
Historical cost		$ 1,012,873	[1]	$ 899,024	[1]	$ 1,047,797
Accumulated depreciation		(291,538)		(308,917)		(418,340)
Net book value		721,335		590,107		$ 629,457
Offshore Support Vessels, Anchor Handling Towing Supply
Historical cost	[1],[2]	50,189		94,078
Accumulated depreciation	[2]	(31,779)		(73,095)
Net book value	[2]	18,410		20,983
Fast Support Vessels
Historical cost	[1],[3]	375,747		388,460
Accumulated depreciation	[3]	(104,739)		(101,295)
Net book value	[3]	271,008		287,165
Offshore Support Vessels, Supply
Historical cost	[1]	238,624		44,958
Accumulated depreciation		(15,991)		(8,471)
Net book value		222,633		36,487
Offshore Support Vessels, Specialty
Historical cost	[1]			14,805
Accumulated depreciation				(10,466)
Net book value				4,339
Offshore Support Vessels, Liftboats
Historical cost	[1]	321,751		327,028
Accumulated depreciation		(117,364)		(93,166)
Net book value		204,387		233,862
Crew Transfer Vessels
Historical cost	[1]	3,163		5,032
Accumulated depreciation		(3,138)		(4,518)
Net book value		25		514
General Machinery and Spares
Historical cost	[1]	7,746		7,650
Accumulated depreciation		(7,733)		(7,648)
Net book value		13		2
Property, Plant and Equipment, Other Types
Historical cost	[1],[4]	15,653		17,013
Accumulated depreciation	[4]	(10,794)		(10,258)
Net book value	[4]	$ 4,859		$ 6,755
[1]	Includes property and equipment acquired in business acquisitions at acquisition date fair value, and net of the impact of recognized impairment charges.
[2]	Anchor Handling Towing (“AHTS”).
[3]	Fast support vessels (“FSVs”)
[4]	Includes land, buildings, leasehold improvements, vehicles and other property and equipment.

Nature of Operations and Acco_9

Nature of Operations and Accounting Policies - Schedule of Deferred Gain Activity (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Balance at end of year	$ 0
Sale-leaseback and Financed Equipment Sales
Balance at beginning of year	11,026,000	$ 23,553,000
Amortization of deferred gains		(8,037,000)
Reclass of gain to Retained Earnings	(11,026,000)
Recognition of deferred gains included in losses on asset dispositions and impairments, net		(4,490,000)
Balance at end of year		11,026,000
Vessel Sales to Fifty Percent or Less Owned Subsidiaries
Balance at beginning of year	793,000	1,453,000
Amortization of deferred gains		(25,000)
Other	$ (793,000)	(635,000)
Balance at end of year		$ 793,000

Nature of Operations and Acc_10

Nature of Operations and Accounting Policies - Schedule of Accumulated Other Comprehensive (Loss) Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Accumulated Other Comprehensive Income Loss [Line Items]
Balance	$ 478,924	$ 565,351	$ 511,097
Other comprehensive (loss) income	1,242	18,163	(4,349)
Income tax benefit (expense)		(173)	46
Balance	401,836	478,924	565,351
Accumulated Foreign Currency Adjustment Attributable to Parent
Accumulated Other Comprehensive Income Loss [Line Items]
Balance	4,685	(15,472)	(13,195)
Other comprehensive (loss) income	2,112	20,157	(2,277)
Balance	6,797	4,685	(15,472)
Accumulated Loss, Net, Cash Flow Hedge, Parent
Accumulated Other Comprehensive Income Loss [Line Items]
Balance	(3,137)	(1,316)	702
Other comprehensive (loss) income	(870)	(1,994)	(1,972)
Income tax benefit (expense)		173	(46)
Balance	(4,007)	(3,137)	(1,316)
AOCI Attributable to Parent
Accumulated Other Comprehensive Income Loss [Line Items]
Balance	1,548	(16,788)	(12,493)
Other comprehensive (loss) income	1,242	18,163	(4,249)
Income tax benefit (expense)		173	(46)
Balance	2,790	1,548	(16,788)
Accumulated Foreign Currency Adjustment Attributable to Noncontrolling Interest
Accumulated Other Comprehensive Income Loss [Line Items]
Balance	(1,445)	(1,445)	(1,357)
Other comprehensive (loss) income			(88)
Balance	(1,445)	(1,445)	(1,445)
Accumulated Gain (Loss), Net, Cash Flow Hedge, Noncontrolling Interest
Accumulated Other Comprehensive Income Loss [Line Items]
Balance	(11)	(11)	1
Other comprehensive (loss) income			(12)
Balance	(11)	(11)	(11)
AOCI Attributable to Noncontrolling Interest
Accumulated Other Comprehensive Income Loss [Line Items]
Balance	18,336	(4,395)	(881)
Other comprehensive (loss) income	1,242	18,163	(4,349)
Income tax benefit (expense)		173	(46)
Balance	$ 1,242	$ 18,336	$ (4,395)

Transformation, Facility Rest_3

Transformation, Facility Restructuring and Severance Charges - Additional Information (Details) - Transformation Plan - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Restructuring Cost And Reserve [Line Items]
Restructuring and related activities, description	The transformation plan, which began in the third quarter of 2019 and extended through the third quarter of 2020 (the “Transformation Plan”), included a workforce reduction, organization restructuring, facility consolidations and other cost reduction measures and efficiency initiatives across the Company’s geographic regions. These initiatives impacted all of the Company’s reportable segments and are expected to result in annualized recurring savings of at least $8.0 million. The Company continues to evaluate additional opportunities for further cost reductions to adapt to changing conditions caused by COVID-19 and other market conditions.
Restructuring charges	$ 1,187,000	$ 3,718,000
Severance charges	1,100,000
Other restructuring charges	62,000	$ 339,000
Restructuring Costs	4,900,000
Minimum
Restructuring Cost And Reserve [Line Items]
Expected annualized recurring savings	$ 8,000,000

Transformation, Facility Rest_4

Transformation, Facility Restructuring and Severance Charges - Schedule of Components of Restructuring Charges (Details) - Transformation Plan - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Restructuring Cost And Reserve [Line Items]
Severance Charges	$ 1,125	$ 3,379
Other Charges	62	339
Total Charges	1,187	3,718
UNITED STATES
Restructuring Cost And Reserve [Line Items]
Severance Charges	275	2,995
Other Charges	31	307
Total Charges	306	3,302
Middle East and Asia
Restructuring Cost And Reserve [Line Items]
Severance Charges	665	184
Other Charges	31	31
Total Charges	696	215
Europe
Restructuring Cost And Reserve [Line Items]
Severance Charges	185	200
Total Charges	$ 185	$ 200

Business Acquisitions - Additio

Business Acquisitions - Additional Information (Details) - SEACOR Offshore Delta LLC $ in Millions	12 Months Ended
	Dec. 31, 2020USD ($)Vessel	Jun. 30, 2020USD ($)Vessel	May 31, 2020
Sale And Purchase Agreement
Equity Method Investment Ownership Percentage		100.00%
Purchase price payable for membership interest		$ 28.2
Purchase price payable to sellers at closing of transaction		8.4
Purchase price for membership interests annual installment payment in first year		1
Purchase price for membership interests annual installment payment in second year		2.5
Purchase price for membership interests annual installment payment in third year		2.5
Purchase price for membership interests annual installment payment in fourth year		$ 13.7
Purchase price fixed accrued interest rate in first year		1.50%
Purchase price fixed accrued interest rate in second year		7.00%
Purchase price fixed accrued interest rate in third year		7.50%
Purchase price fixed accrued interest rate in fourth year		8.00%
Sale And Purchase Agreement | Platform Supply Vessels
Number of vessels owned | Vessel	8	8
Number of vessels owned with high specification | Vessel	2
Number of vessels owned with identical specification | Vessel	6
Deferred Purchase Agreements | Platform Supply Vessels
Business acquisition, aggregate amount outstanding	$ 95.3	$ 100.8
Business acquisition, amortization period of purchase price	10 years
Debt instrument, description of floating interest rate basis	three-month LIBOR plus 4.0
Debt instrument, basis spread on floating interest rate	4.00%
Number of vessels delivered to the company | Vessel	7
SEACOR Offshore Asia | Sale And Purchase Agreement
Equity Method Investment Ownership Percentage			50.00%

Business Acquisitions - Summary

Business Acquisitions - Summary of Purchase Price Allocation of Acquired Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Jun. 30, 2020	Dec. 31, 2019
Schedule Of Investments [Line Items]
Equity Investment In SEACOR Offshore Delta (f/k/a SEACOSCO)	$ (75,308)		$ (120,831)
SEACOR Offshore Delta LLC
Schedule Of Investments [Line Items]
Current Assets		$ 7,700
Fixed Assets		142,282
Current Liabilities		(23,929)
Book Value of Debt Acquired		100,759
Discount on Debt Acquired		25,190
Fair Value of Debt Acquired		(75,569)
Total Cost Basis for Purchase		50,484
Purchase Price		(28,150)
Acquisition costs		(112)
Equity Investment In SEACOR Offshore Delta (f/k/a SEACOSCO)		(22,222)
Total Cost Basis for Purchase		$ (50,484)

Equipment Acquisitions and Di_3

Equipment Acquisitions and Dispositions - Additional Information (Details)		Jan. 12, 2021USD ($)	Jan. 12, 2021GBP (£)	Dec. 31, 2020USD ($)Vessel		Dec. 31, 2019USD ($)Vessel		Dec. 31, 2019GBP (£)Vessel		Dec. 31, 2018USD ($)
Property Plant And Equipment [Line Items]
Capital expenditures and payments on equipment				$ 20,800,000		$ 44,800,000				$ 35,600,000
Issuance of stock										$ 42,996,000
Acquired				4	[1]	4	[2]	4	[2]	11	[2]
Gain (loss) on disposition of property, plant and equipment						$ 5,500,000				$ 5,700,000
Proceeds from sale of business				$ 20,674,000		55,321,000				10,655,000
Proceeds from deposits						1,100,000				100,000
Net book value				753,662,000		660,913,000
Proceeds from sale of property, plant, and equipment, including deposits						55,300,000				12,300,000
Proceeds from sale of property, plant, and equipment, excluding deposits for future vessel sales						54,200,000				$ 12,200,000
ERRV Fleet Business
Property Plant And Equipment [Line Items]
Gain (loss) on disposition of property, plant and equipment						(9,100,000)
Proceeds from sale of business						27,390,000
Net book value						23,400,000
Additional consideration				$ 0		$ 5,200,000		£ 4,000,000
Crew Transfer Vessels
Property Plant And Equipment [Line Items]
Acquired | Vessel				41
Number of additional joint ventures held interests | Vessel				5
Crew Transfer Vessels | Subsequent Event
Property Plant And Equipment [Line Items]
Sale of equity percentage		100.00%	100.00%
Aggregate purchase price | £			£ 32,800,000
Issuance of stock		$ 42,600,000
Debt outstanding under revolving credit facility | £			£ 20,400,000
Windcat Workboats | Subsequent Event
Property Plant And Equipment [Line Items]
Gain (loss) on disposition of property, plant and equipment		$ 22,800,000
Vessel Under Construction
Property Plant And Equipment [Line Items]
Gain (loss) on disposition of property, plant and equipment				$ 1,200,000
Proceeds from property, plant, and equipment, including deposits and gain on sale				21,600,000
Proceeds from sale of business				20,700,000
Proceeds from deposits				$ 900,000
Vessel under Construction and Other Equipment
Property Plant And Equipment [Line Items]
Number of equipment sold | Vessel				1
Anchor Handling Towing Supply
Property Plant And Equipment [Line Items]
Number of equipment sold | Vessel				2		1		1
Specialty Vessel
Property Plant And Equipment [Line Items]
Number of equipment sold | Vessel				1
Fast Support Vessels
Property Plant And Equipment [Line Items]
Acquired	[2]					2		2		6
Number of equipment sold | Vessel				4		5		5
Vessels | ERRV Fleet Business
Property Plant And Equipment [Line Items]
Number of equipment sold | Vessel						18		18
Liftboats
Property Plant And Equipment [Line Items]
Number of equipment sold | Vessel						3		3
Platform Supply Vessels
Property Plant And Equipment [Line Items]
Number of equipment sold | Vessel						5		5
[1]	Excludes three CTVs as assets held for sale and seven PSVs acquired as part of the SEACOSCO Acquisition (See “Note 3. Business Acquisitions”).
[2]	Ex cludes two CTVs as assets held for sale.

Equipment Acquisitions and Di_4

Equipment Acquisitions and Dispositions - Schedule of Vessel Acquired and Disposed (Details)		12 Months Ended
		Dec. 31, 2020Vessel		Dec. 31, 2019		Dec. 31, 2018
Property Plant And Equipment [Line Items]
Acquired		4	[1]	4	[2]	11	[2]
Removed from service		10	[3]	14		12	[4]
Fast Support Vessels
Property Plant And Equipment [Line Items]
Acquired	[2]			2		6
Removed from service		4	[3]	5		9	[4]
Offshore Support Vessels, Supply
Property Plant And Equipment [Line Items]
Acquired		4	[1]	2	[2]	5	[2]
Removed from service		1	[3]	5
Offshore Support Vessels, Liftboats
Property Plant And Equipment [Line Items]
Removed from service		1	[3]	3		2	[4]
Anchor Handling Towing Supply
Property Plant And Equipment [Line Items]
Removed from service		2	[3]	1		1	[4]
Crew Transfer Vessels
Property Plant And Equipment [Line Items]
Acquired		41
Specialty Vessel
Property Plant And Equipment [Line Items]
Removed from service	[3]	2
[1]	Excludes three CTVs as assets held for sale and seven PSVs acquired as part of the SEACOSCO Acquisition (See “Note 3. Business Acquisitions”).
[2]	Ex cludes two CTVs as assets held for sale.
[3]	Excludes three
[4]	Excludes one CTV from assets held for sale.

Equipment Acquisitions and Di_5

Equipment Acquisitions and Dispositions - Schedule of Vessel Acquired and Disposed (Parenthetical) (Details)	12 Months Ended
	Dec. 31, 2020Vessel	Dec. 31, 2019Vessel	Dec. 31, 2018Vessel
Property Plant And Equipment [Line Items]
Number of equipment removed from service excludes from major equipment dispositions	3
Crew Transfer Vessels
Property Plant And Equipment [Line Items]
Number of equipment held for sale excluded from deliveries of offshore support vessels	3	2	2
Number of equipment held for sale excluded from major equipment dispositions			1
Platform Supply Vessels
Property Plant And Equipment [Line Items]
Number of equipment acquired excludes from deliveries of offshore support vessels	7
Anchor Handling Towing Supply
Property Plant And Equipment [Line Items]
Number of equipment removed from service excludes from major equipment dispositions	2
Specialty Vessel
Property Plant And Equipment [Line Items]
Number of equipment removed from service excludes from major equipment dispositions	1

Investments, at Equity, and A_3

Investments, at Equity, and Advances to 50% or Less Owned Companies - Schedule of Equity Investments (Details) - USD ($) $ in Thousands		3 Months Ended								12 Months Ended
		Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 20, 2018
Schedule Of Investments [Line Items]
Ownership percentage													49.00%
Investments at equity		$ 75,308				$ 120,831				$ 75,308	$ 120,831
Current assets		178,696				194,661				178,696	194,661
Current liabilities		131,804				120,297				131,804	120,297
Operating Revenues		36,044	$ 36,201	$ 33,925	$ 35,667	42,478	$ 46,996	$ 45,014	$ 39,965	141,837	174,453	$ 179,161
Operating (Loss) Income										83,346	100,070	82,979
Net Loss		$ (38,847)	$ (18,077)	$ (6,066)	$ (19,992)	$ (21,918)	$ (18,240)	$ (30,264)	$ (28,273)	$ (82,982)	$ (98,695)	(82,052)
Minimum
Schedule Of Investments [Line Items]
Ownership percentage		20.00%								20.00%
Maximum
Schedule Of Investments [Line Items]
Ownership percentage		50.00%				50.00%				50.00%	50.00%
MexMar
Schedule Of Investments [Line Items]
Ownership percentage		49.00%								49.00%
Investments at equity		$ 50,037				$ 54,249				$ 50,037	$ 54,249
SeaCosco
Schedule Of Investments [Line Items]
Ownership percentage	[1]	50.00%								50.00%
Investments at equity	[1]					37,480					37,480
OSV Partners
Schedule Of Investments [Line Items]
Ownership percentage	[2]	30.40%								30.40%
Investments at equity	[2]	$ 9,094				10,668				$ 9,094	10,668
SEACOR Marlin LLC
Schedule Of Investments [Line Items]
Ownership percentage		49.00%								49.00%
Investments at equity		$ 7,979				7,929				$ 7,979	7,929
MEXMAR Offshore
Schedule Of Investments [Line Items]
Ownership percentage	[3]	49.00%								49.00%
Investments at equity	[3]	$ 1,960								$ 1,960
Offshore Vessel Holdings
Schedule Of Investments [Line Items]
Ownership percentage		49.00%								49.00%
Investments at equity		$ 2,388				7,905				$ 2,388	7,905
Other Offshore Marine Services Joint Ventures
Schedule Of Investments [Line Items]
Investments at equity		$ 3,850				2,600				$ 3,850	2,600
Other Offshore Marine Services Joint Ventures | Minimum
Schedule Of Investments [Line Items]
Ownership percentage		20.00%								20.00%
Other Offshore Marine Services Joint Ventures | Maximum
Schedule Of Investments [Line Items]
Ownership percentage		50.00%								50.00%
All Other Excluding MexMar, Falcon Global, Sea-Cat Crewzer and Sea-Cat Crewzer II
Schedule Of Investments [Line Items]
Operating and administrative										$ 142,228	116,517	75,529
Depreciation										27,044	27,412	25,359
Costs and expenses										169,272	143,929	100,888
Loss on Asset Dispositions and Impairments, Net											(166)	(262)
Operating (Loss) Income										(8,491)	(7,405)	4,013
Net Loss										(18,229)	(36,816)	(14,861)
All Other Excluding MexMar, Falcon Global, Sea-Cat Crewzer and Sea-Cat Crewzer II | Equity Method Investment, Nonconsolidated Investee or Group of Investees
Schedule Of Investments [Line Items]
Current assets		$ 109,687				106,051				109,687	106,051
Noncurrent assets		259,424				607,541				259,424	607,541
Current liabilities		109,074				104,423				109,074	104,423
Noncurrent liabilities		$ 115,626				$ 331,357				115,626	331,357
Operating Revenues										$ 160,781	$ 136,690	$ 105,163
[1]	The Company acquired the remaining 50% of the SEACOSCO Joint Venture that it did not own on June 30, 2020.
[2]	The Company owns 66.7 % of the General Partner and 29.7 % of the limited Partner .
[3]	This Joint Venture holds the investment in UP Offshore .

Investments, at Equity, and A_4

Investments, at Equity, and Advances to 50% or Less Owned Companies - Schedule of Equity Investments (Parenthetical) (Details)		Dec. 31, 2020	Dec. 20, 2018
Schedule Of Investments [Line Items]
Equity method investment, ownership percentage			49.00%
General Partner
Schedule Of Investments [Line Items]
Equity method investment, ownership percentage		66.70%
Limited Partner
Schedule Of Investments [Line Items]
Equity method investment, ownership percentage		29.70%
SeaCosco
Schedule Of Investments [Line Items]
Equity method investment, ownership percentage	[1]	50.00%
[1]	The Company acquired the remaining 50% of the SEACOSCO Joint Venture that it did not own on June 30, 2020.

Investments, at Equity, and A_5

Investments, at Equity, and Advances to 50% or Less Owned Companies - Additional Information (Details)		Dec. 18, 2019USD ($)	Dec. 28, 2018USD ($)	Dec. 20, 2018USD ($)	Sep. 28, 2018USD ($)Vessel	Sep. 13, 2018USD ($)	Dec. 31, 2020USD ($)Vessel	Dec. 31, 2019USD ($)VesselEquipment	Dec. 31, 2018USD ($)
Schedule Of Investments [Line Items]
Consolidated retained earnings							$ 20,700,000	$ 14,700,000
Revenue from related parties								0
Contributed capital				$ 10,000,000
Equity method investment, ownership percentage				49.00%
Equity method investment, other than temporary impairment							$ 0	$ 0	$ 1,200,000
Maximum
Schedule Of Investments [Line Items]
Equity method investment, ownership percentage							50.00%	50.00%
Minimum
Schedule Of Investments [Line Items]
Equity method investment, ownership percentage							20.00%
MEXICO
Schedule Of Investments [Line Items]
Number of vessels owned | Vessel								3
Mexmar Offshore International
Schedule Of Investments [Line Items]
Equity method investment, ownership percentage				49.00%
Noncontrolling interest, ownership percentage by noncontrolling owners				51.00%
Offshore Vessel Holdings
Schedule Of Investments [Line Items]
Contributed capital								$ 10,000,000
Noncontrolling interest, ownership percentage by noncontrolling owners			51.00%
Noncontrolling Interest, ownership percentage by parent			49.00%
Payments to acquire interest in joint venture			$ 4,900,000
Financing agreement								$ 2,400,000
Offshore Support Vessels, Supply
Schedule Of Investments [Line Items]
Number of vessels owned | Vessel								1
Offshore Support Vessels, Supply | Offshore Vessel Holdings
Schedule Of Investments [Line Items]
Number of equipment operated | Equipment								3
Jack up Drillings [Member] | Offshore Vessel Holdings
Schedule Of Investments [Line Items]
Number of equipment operated | Equipment								2
F S V Offshore Support Vessels | Offshore Vessel Holdings
Schedule Of Investments [Line Items]
Number of equipment operated | Equipment								1
MexMar
Schedule Of Investments [Line Items]
Capital distributions from equity investees							$ 0	$ 0	9,800,000
Revenue from related parties							$ 300,000	300,000	300,000
Equity method investment, ownership percentage							49.00%
Number of vessels owned | Vessel							16
MexMar | Offshore Support Vessels
Schedule Of Investments [Line Items]
Number of equipment operated | Vessel							16
OSV Partners
Schedule Of Investments [Line Items]
Number of equipment operated | Vessel					5
Revenue from related parties									600,000
Contributed capital					$ 5,000,000
Investment in affiliates, amount of preferred equity offering participated					5,000,000
Payments to acquire interest in subsidiaries and affiliates, total		$ 1,100,000			1,100,000
Commitment to invest additional funds if call by general partner					1,100,000
Payments to acquire loans receivable					$ 2,100,000
Equity method investment, ownership percentage	[1]						30.40%
SEACOR Marlin LLC
Schedule Of Investments [Line Items]
Equity method investment, ownership, percent sold						51.00%
Proceeds from divestiture of interest in joint venture						$ 8,000,000
Gain (loss) on disposition of business						$ 400,000
Equity method investment, ownership percentage							49.00%
Other Offshore Marine Services Joint Ventures
Schedule Of Investments [Line Items]
Number of equipment operated | Vessel							0
Capital distributions from equity investees							$ 2,100,000	2,100,000
Revenue from related parties									300,000
Return of capital equity method investment								500,000
Equity method investment, other than temporary impairment									$ 1,200,000
Other Offshore Marine Services Joint Ventures | Maximum
Schedule Of Investments [Line Items]
Revenue from related parties								$ 100,000
Equity method investment, ownership percentage							50.00%
Other Offshore Marine Services Joint Ventures | Minimum
Schedule Of Investments [Line Items]
Equity method investment, ownership percentage							20.00%
[1]	The Company owns 66.7 % of the General Partner and 29.7 % of the limited Partner .

Construction Reserve Funds - Ad

Construction Reserve Funds - Additional Information (Details) $ in Millions	12 Months Ended
	Dec. 31, 2020USD ($)ExtensionPeriod	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)
Restricted Cash And Investments [Abstract]
Construction reserve funds commitment period	3 years
Number of extension period | ExtensionPeriod	2
Construction reserve funds extension period	1 year
Short-term construction reserve funds	$ 4.2
Construction reserve fund withdrawals	$ 9.1	$ 15.2	$ 17.3

Leases - Additional Information

Leases - Additional Information (Details) $ in Thousands	Jan. 01, 2019USD ($)	Dec. 31, 2020USD ($)Vessel	Dec. 31, 2019USD ($)
Lessee Lease Description [Line Items]
Right-of-Use Asset - Operating Leases		$ 7,134	$ 16,537
Operating Lease, Liability		11,375
Retained earnings		(51,839)	27,076
Operating Lease, Impairment Loss		$ 5,900	$ 5,300
Number of Operating Leases Impaired		2	1
Anchor Handling Towing Supply
Lessee Lease Description [Line Items]
Number of operating leases on equipment | Vessel		2
Liftboats
Lessee Lease Description [Line Items]
Number of operating leases on equipment | Vessel		1
Fast Support Vessels
Lessee Lease Description [Line Items]
Number of operating leases on equipment | Vessel		1
Vessels | Minimum
Lessee Lease Description [Line Items]
Operating lease, lease terms (in duration)		8 months
Vessels | Maximum
Lessee Lease Description [Line Items]
Operating lease, lease terms (in duration)		12 months
Other Equipment | Minimum
Lessee Lease Description [Line Items]
Operating lease, lease terms (in duration)		11 months
Other Equipment | Maximum
Lessee Lease Description [Line Items]
Operating lease, lease terms (in duration)		312 months
Accounting Standards Update 2016-02
Lessee Lease Description [Line Items]
Right-of-Use Asset - Operating Leases	$ 33,700
Operating Lease, Liability	31,900
Accounting Standards Update 2016-02 | Change in Accounting Principle for Unamortized Deferred Gains
Lessee Lease Description [Line Items]
Cumulative effect on retained earnings, Before tax	11,000
Cumulative effect on retained earnings, Tax	2,300
Accounting Standards Update 2016-02 | Cumulative Effect, Period of Adoption, Adjustment | Change in Accounting Principle for Equipment, Office and Land Leases
Lessee Lease Description [Line Items]
Retained earnings	1,700
Accounting Standards Update 2016-02 | Cumulative Effect, Period of Adoption, Adjustment | Change in Accounting Principle for Unamortized Deferred Gains
Lessee Lease Description [Line Items]
Retained earnings	$ 8,700

Leases - Summary of Future Mini

Leases - Summary of Future Minimum Payments For Leases (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Operating Leases
2021	$ 7,855
2022	639
2023	628
2024	559
2025	539
Years subsequent to 2025	4,215
Operating lease payments due	14,435
Interest component	(3,060)
Total operating leases	11,375
Current portion of long-term operating lease liabilities	(7,030)	$ (14,896)
Long-term operating lease liabilities	4,345	$ 9,255
Finance Leases
2021	42
2022	39
2023	39
2024	36
Total finance leases	156
Interest component	(15)
Finance Leases	141
Current portion of long-term finance lease liabilities	(36)
Long-term finance lease liabilities	$ 105

Leases - Summary of Components

Leases - Summary of Components of Leases Expense (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019
Leases [Abstract]
Operating lease expense	[1]	$ 6,205	$ 13,442
Finance lease cost:
Amortization of finance lease asset	[1]	11
Interest on lease liabilities	[2]	1
Short-term lease costs	[1]	1,320	2,398
Total lease expense		$ 7,537	$ 15,840
[1]	Included in selling, general and administrative expenses and amortization costs in the consolidated statements of loss.
[2]	Included in interest expense in the consolidated statements of loss.

Leases - Summary of Supplementa

Leases - Summary of Supplemental Cash Flow Information Related to Leases (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2020USD ($)
Leases [Abstract]
Operating cash flows from operating leases	$ 14,785
Right-of-use assets obtained for operating lease liabilities	1,706
Right-of-use assets obtained for finance lease liabilities	$ 140

Leases - Summary of Other Infor

Leases - Summary of Other Information Related to Leases (Details)	Dec. 31, 2020
Leases [Abstract]
Weighted average remaining lease term, in years - operating leases	7 years 7 months 6 days
Weighted average remaining lease term, in years - finance leases	4 years 2 months 12 days
Weighted average discount rate - operating leases	4.70%
Weighted average discount - finance leases	5.30%

Long Term Debt - Schedule of Lo

Long Term Debt - Schedule of Long-term Debt Obligations (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 521,877	$ 405,093
Current portion due within one year	(32,377)	(17,802)
Unamortized debt discount	(44,864)	(26,343)
Deferred financing costs	(4,126)	(5,234)
Long-term debt, less current portion	440,510	355,714
Recourse Long-Term Debt
Debt Instrument [Line Items]
Long-term Debt, Gross	399,028	282,244
Non-Recourse Long-Term Debt
Debt Instrument [Line Items]
Long-term Debt, Gross	122,849	122,849
Convertible Senior Notes | Recourse Long-Term Debt
Debt Instrument [Line Items]
Long-term Debt, Gross	125,000	125,000
SEACOR Marine Foreign Holdings Credit Facility | Recourse Long-Term Debt
Debt Instrument [Line Items]
Long-term Debt, Gross	100,750	113,750
Falcon Global USA Term Loan Facility | Non-Recourse Long-Term Debt
Debt Instrument [Line Items]
Long-term Debt, Gross	102,349	102,349
Sea-Cat Crewzer III Term Loan Facility | Recourse Long-Term Debt
Debt Instrument [Line Items]
Long-term Debt, Gross	21,653	24,128
SEACOR Offshore Delta (f/k/a SEACOSCO) Acquisition Debt | Recourse Long-Term Debt
Debt Instrument [Line Items]
Long-term Debt, Gross	19,705
SEACOR Delta (f/k/a SEACOSCO) Shipyard Financing | Recourse Long-Term Debt
Debt Instrument [Line Items]
Long-term Debt, Gross	95,317
Falcon Global USA Revolver | Non-Recourse Long-Term Debt
Debt Instrument [Line Items]
Long-term Debt, Gross	15,000	15,000
SEACOR Alpine Shipyard Financing | Recourse Long-Term Debt
Debt Instrument [Line Items]
Long-term Debt, Gross	31,103	10,534
SEACOR 88/888 Term Loan | Recourse Long-Term Debt
Debt Instrument [Line Items]
Long-term Debt, Gross	5,500	5,500
SEACOR 88/888 Term Loan | Non-Recourse Long-Term Debt
Debt Instrument [Line Items]
Long-term Debt, Gross	5,500	5,500
BNDES Equipment Construction Finance Notes | Recourse Long-Term Debt
Debt Instrument [Line Items]
Long-term Debt, Gross		3,332
Windcat Workboats Facilities | Current Liabilities
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 27,626	$ 24,537

Long Term Debt - Schedule of _2

Long Term Debt - Schedule of Long-term Debt Obligations (Parenthetical) (Details)	12 Months Ended
	Dec. 31, 2020Vessel		Dec. 31, 2019	[2]	Dec. 31, 2018	[2]
Debt Instrument [Line Items]
Number of vessels acquired	4	[1]	4		11
SEACOR Delta (f/k/a SEACOSCO) Shipyard Financing | SeaCosco
Debt Instrument [Line Items]
Number of vessels acquired	8
[1]	Excludes three CTVs as assets held for sale and seven PSVs acquired as part of the SEACOSCO Acquisition (See “Note 3. Business Acquisitions”).
[2]	Ex cludes two CTVs as assets held for sale.

Long Term Debt - Schedule of _3

Long Term Debt - Schedule of Long-term Debt Maturities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Debt Disclosure [Abstract]
2021	$ 32,377
2022	38,484
2023	244,983
2024	134,523
2025	11,365
Years subsequent to 2025	60,145
Long-term Debt, Gross	$ 521,877	$ 405,093

Long Term Debt - Additional Inf

Long Term Debt - Additional Information (Details) $ / shares in Units, € in Millions

Feb. 24, 2021USD ($)

Dec. 18, 2020USD ($)

Mar. 03, 2020EUR (€)

Sep. 26, 2018USD ($)

Jul. 05, 2018USD ($)

May 02, 2018USD ($)$ / sharesshares

Apr. 30, 2018USD ($)$ / sharesshares

Dec. 31, 2020USD ($)

Dec. 31, 2020EUR (€)

Dec. 31, 2019USD ($)

Dec. 31, 2018USD ($)

Dec. 31, 2017USD ($)

Dec. 31, 2016USD ($)

Jun. 29, 2020Vessel

Oct. 31, 2019Vessel

Oct. 31, 2018USD ($)

Feb. 08, 2018USD ($)

May 24, 2016EUR (€)

Apr. 21, 2016EUR (€)

Dec. 01, 2015USD ($)$ / shares

Debt Instrument [Line Items]

Repayments of long-term debt, total

$ 22,601,000

$ 23,974,000

$ 41,932,000

Debt instrument, increase (decrease), net,

$ 30,100,000

Loss on extinguishment of debt

$ 638,000

Number of additional vessels owned | Vessel

2

Long-term Debt Obligation

Debt Instrument [Line Items]

Letters of credit outstanding, amount

500,000

Carlyle Group

Debt Instrument [Line Items]

Convertible debt, total

$ 175,000,000

Convertible Senior Notes Converted to Warrants | Carlyle Group

Debt Instrument [Line Items]

Debt instrument, convertible, conversion ratio

37.73

37.73

Debt instrument, face amount

$ 1,000

$ 1,000

Class of warrant or right, exercise price of warrants or rights | $ / shares

$ 0.01

$ 0.01

Debt conversion, original debt, amount

$ 50,000,000

$ 50,000,000

Debt conversion, converted instrument, shares issued | shares

1,886,792

1,900,000

Debt instrument, convertible, conversion price | $ / shares

$ 26.50

$ 26.50

Carlyle Warrants

Debt Instrument [Line Items]

Class of warrant or right, exercise price of warrants or rights | $ / shares

$ 0.01

Warrants and rights outstanding, term

25 years

SEACOR Alpine Shipyard Financing

Debt Instrument [Line Items]

Debt instrument, interest rate

5.00%

Percentage of amount of loan financed

70.00%

Debt instrument, term of delivery

4 years

Windcat Workboats Facilities

Debt Instrument [Line Items]

Line of credit facility, maximum borrowing capacity | €

€ 25

Debt instrument, maturity date

Dec. 31, 2021

Debt instrument, extended maturity date

Dec. 31, 2022

Application fee paid in conjunction with amendment and amortized over credit facility term | €

€ 0.1

Proceeds from lines of credit | €

€ 1

Debt instrument, increase (decrease), net,

$ 1,100,000

Loan Facility With DNB Bank ASA

Debt Instrument [Line Items]

Line of credit facility, maximum borrowing capacity

$ 130,000

Debt instrument, interest rate, effective percentage

4.00%

Debt instrument, maturity period

2023

Debt instrument, periodic payment, principal

$ 3,300,000

Loan Facility With DNB Bank ASA | Interest Rate Swap

Debt Instrument [Line Items]

Derivative, notional amount

$ 65,000,000

Other DNB Credit Facilities

Debt Instrument [Line Items]

Repayments of lines of credit

101,300,000

Long-term debt, total

99,900,000

Interest payable

1,400,000

Loss on extinguishment of debt

$ 600,000

BNDES Equipment Construction Finance Notes

Debt Instrument [Line Items]

Number of vessels purchased from the company | Vessel

2

Convertible Senior Notes 3.75%

Debt Instrument [Line Items]

Debt instrument, interest rate

4.25%

4.25%

3.75%

Convertible debt, total

$ 125,000,000

$ 125,000,000

$ 175,000,000

Debt instrument, convertible, conversion ratio

23.26

Debt instrument, face amount

$ 1,000

Three Point Seven Five Percentage Convertible Notes

Debt Instrument [Line Items]

Debt instrument, interest rate, effective percentage

7.95%

Embedded derivative, fair value of embedded derivative liability

$ 27,300,000

Sea-Cat Crewzer III

Debt Instrument [Line Items]

Repayments of long-term debt, total

$ 3,100,000

Debt instrument, interest rate, effective percentage

2.76%

Debt instrument, face amount | €

€ 27.6

Proceeds from issuance of debt

$ 7,100,000

$ 22,800,000

Debt issuance costs, gross

$ 2,700,000

Term Loan to Acquire Two Vessels

Debt Instrument [Line Items]

Debt instrument, interest rate, effective percentage

3.75%

Debt instrument, face amount

$ 11,000,000

Claims recoverable amount under borrowings

$ 5,500,000

Claims recoverable under borrowings percentage of obligations outstanding

50.00%

Debt instrument, maturity year

2023

2023

Term Loan to Acquire Two Vessels | Interest Rate Swap

Debt Instrument [Line Items]

Derivative, notional amount

$ 5,500,000

FGUSA Omnibus Amendment | Term and Revolving Loan Facility

Debt Instrument [Line Items]

Debt agreement maximum borrowing capacity

$ 131,100,000

Seventh FGUSA Credit Facility Amendment | Subsequent Event

Debt Instrument [Line Items]

Repayment terms

the extension from March 2021 to June 2021 of the commencement of monthly repayment of the term loan, with payments being the lesser of (a) $0.8 million and (b) the amount outstanding under the term loan

Repayments of long-term debt, total

$ 800,000

Extension term of Guaranty

3 months

Deferred Purchase Agreements | SEACOR Offshore Delta (f/k/a SEACOSCO)

Debt Instrument [Line Items]

Purchase price payable for equity method investment in first year

$ 1,000,000

Purchase price payable for equity method investment in second year

2,500,000

Purchase price payable for equity method investment in third year

2,500,000

Purchase price payable for equity method investment in fourth year

$ 13,700,000

Purchase price fixed accrued interest rate in first year

1.50%

Purchase price fixed accrued interest rate in second year

7.00%

Purchase price fixed accrued interest rate in third year

7.50%

Purchase price fixed accrued interest rate in fourth year

8.00%

Deferred Purchase Agreements | SEACOR Offshore Delta (f/k/a SEACOSCO) | Platform Supply Vessels

Debt Instrument [Line Items]

Equity method investment, amortization of purchase price

10 years

10 years

Debt instrument, description of floating interest rate basis

three-month LIBOR plus 4.0%

three-month LIBOR plus 4.0%

Debt instrument, basis spread on floating interest rate

4.00%

4.00%

Tax Refund Agreement

Debt Instrument [Line Items]

Estimated tax refund receivable

$ 31,200,000

Income Taxes - Additional Infor

Income Taxes - Additional Information (Details) - USD ($) $ in Millions	Jun. 26, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Taxes [Line Items]
Effective income tax rate reconciliation, at federal statutory Income tax rate, percent		21.00%	21.00%	21.00%	35.00%
Income tax benefit and equity in earnings (losses)		50.00%
Income tax refunds		$ 1.6
Foreign tax credits		0.3
Expected tax refund		$ 0.4
Increase (decrease) in transition tax liability			$ 2.3
Current income tax expense (benefit), nonqualified withdrawal of funds from capital construction fund				$ 1.4
Effective income tax rate reconciliation, percent, total		23.40%	9.40%	14.60%
Interest expense suspended		$ 4.4	$ 6.6	$ 3.6
Suspended interest deductible		3.3
Interest expense carryforward		$ 11.3
Interest expense suspended, limitation percentage		30.00%
Operating loss carryforwards, percentage of taxable income, utilization limitation		80.00%
Operating loss carryforwards, total		$ 42.2		$ 67.6
Operating loss carryforwards, expiration period				20 years
Operating loss carryforwards, valuation allowance, total		2.5
Tax Refund Agreement
Income Taxes [Line Items]
Expected to cash tax refunds receivable	$ 31.2
Percentage of net operating losses facilitate tax savings	35.00%
Transaction fee	$ 3
Cash tax refunds receivable without restrict to use		23.1
Cash tax refunds receivable with restrict to use		$ 8.1

Income Taxes - Schedule of Inco

Income Taxes - Schedule of Income before Income Tax (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Taxes [Line Items]
Income before income tax expense (benefit) and equity in earnings of 50% or less owned companies	$ (98,107)	$ (84,474)	$ (92,433)
United States
Income Taxes [Line Items]
Income before income tax expense (benefit) and equity in earnings of 50% or less owned companies	(83,560)	(71,833)	(72,540)
Foreign
Income Taxes [Line Items]
Income before income tax expense (benefit) and equity in earnings of 50% or less owned companies	(17,748)	(23,663)	(28,675)
Eliminations
Income Taxes [Line Items]
Income before income tax expense (benefit) and equity in earnings of 50% or less owned companies	$ 3,201	$ 11,022	$ 8,782

Income Taxes - Components of In

Income Taxes - Components of Income Tax Expense (Benefit) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Federal, current	$ (30,838)	$ (6)	$ 5,987
State, current	123	(78)	3
Foreign, current	5,533	5,005	3,307
Current income tax expense	(25,182)	4,921	9,297
Federal, deferred	2,435	(12,594)	(21,466)
State, deferred	(139)	(224)	(1,404)
Foreign, deferred	(38)	(72)	110
Deferred income tax benefit	2,258	(12,890)	(22,760)
Income Tax (Benefit) Expense	$ (22,924)	$ (7,969)	$ (13,463)

Income Taxes - Schedule of Effe

Income Taxes - Schedule of Effective Income Tax Rate Reconciliation (Details)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Statutory rate	(21.00%)	(21.00%)	(21.00%)	(35.00%)
U.S. federal income tax law changes	(11.80%)
SEACOR Holdings share awards to Company personnel	0.30%		0.20%
Exclusion of foreign subsidiaries with accumulated losses and withholding tax	7.70%	7.40%	9.30%
Noncontrolling interests	1.30%	1.70%	(1.60%)
State taxes		(0.30%)	(1.50%)
Return to provision	(0.40%)	2.80%	(0.50%)
Other	0.50%		0.50%
Effective Tax Rate	(23.40%)	(9.40%)	(14.60%)

Income Taxes - Schedule of Defe

Income Taxes - Schedule of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Deferred tax liabilities:
Property and equipment	$ 58,676	$ 63,827
Investments in 50% or Less Owned Companies	2,925	3,039
Other	4,819	10,612
Total deferred tax liabilities	66,420	77,478
Deferred tax assets:
Federal Net Operating Loss Carryforwards	23,061	28,664
Other	10,073	16,561
Total deferred tax assets	33,134	45,225
Valuation Allowance	(2,536)	(1,311)
Total deferred tax assets	30,598	43,914
Net deferred tax liabilities	$ 35,822	$ 33,564

Derivative Instruments and He_3

Derivative Instruments and Hedging Strategies - Schedule of Fair Value of Derivative Assets and Liabilities From Continuing Operations (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Not Designated as Hedging Instrument
Derivative [Line Items]
Derivative Liability	$ 895	$ 5,205
Not Designated as Hedging Instrument | Forward Exchange Contract
Derivative [Line Items]
Derivative Liability	893
Not Designated as Hedging Instrument | Non-current Liabilities
Derivative [Line Items]
Embedded derivative, fair value of embedded derivative liability	2	5,205
Designated as Hedging Instrument | Cash Flow Hedging
Derivative [Line Items]
Derivative Liability	3,698	2,925
Designated as Hedging Instrument | Current Liabilities | Interest Rate Swap | Cash Flow Hedging
Derivative [Line Items]
Derivative Liability	$ 3,698	$ 2,925

Derivative Instruments and He_4

Derivative Instruments and Hedging Strategies - Additional Information (Details) $ in Thousands, € in Millions, £ in Millions	12 Months Ended
	Dec. 31, 2020USD ($)	Dec. 31, 2020GBP (£)	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2020EUR (€)	Dec. 20, 2018
Derivative [Line Items]
Derivative losses on cash flow hedges	$ (2,139)		$ (1,901)	$ (1,939)
Equity method investment, ownership percentage						49.00%
Estimated fair value of derivative instruments from continuing operations	4,600
Credit risk adjustment	300
Interest Rate Swap
Derivative [Line Items]
Derivative losses on cash flow hedges	$ (2,139)		$ (1,901)	(1,939)
Forward Exchange Contract | Windcat Workboats Holdings Ltd
Derivative [Line Items]
Proceeds to be received from sale of business | £		£ 31.5
Maximum
Derivative [Line Items]
Equity method investment, ownership percentage	50.00%		50.00%		50.00%
Minimum
Derivative [Line Items]
Equity method investment, ownership percentage	20.00%				20.00%
Minimum | SEACOR Marine Foreign Holdings
Derivative [Line Items]
Equity method investment, ownership percentage	50.00%				50.00%
Cash Flow Hedging
Derivative [Line Items]
Derivative losses on cash flow hedges	$ (700)		$ (1,300)	$ 1,600
Cash Flow Hedging | Interest Rate Swap | Designated as Hedging Instrument | Windcat Workboats Holdings Ltd
Derivative [Line Items]
Derivative, number of instruments held, total	2				2
Derivative, fixed interest rate	0.03%				0.03%
Derivative, notional amount	$ 20,400				€ 15
Cash Flow Hedging | Interest Rate Swap | Designated as Hedging Instrument | SEACOR 88/888
Derivative [Line Items]
Derivative, fixed interest rate	3.175%				3.175%
Derivative, notional amount	$ 5,500
Cash Flow Hedging | Interest Rate Swap | Designated as Hedging Instrument | MexMar
Derivative [Line Items]
Equity method investment, ownership percentage	49.00%				49.00%
Derivative, number of instruments held, total	5				5
Derivative, notional amount	$ 69,400
Cash Flow Hedging | 3.32% Interest Rate Swap Agreement | Designated as Hedging Instrument | SEACOR Marine Foreign Holdings
Derivative [Line Items]
Derivative, fixed interest rate	3.32%				3.32%
Derivative, notional amount	$ 7,800
Cash Flow Hedging | 3.195% Interest Rate Swap Agreement | Designated as Hedging Instrument | SEACOR Marine Foreign Holdings
Derivative [Line Items]
Derivative, fixed interest rate	3.195%				3.195%
Derivative, notional amount	$ 43,000
Cash Flow Hedging | Maximum | Interest Rate Swap | Designated as Hedging Instrument | MexMar
Derivative [Line Items]
Derivative, fixed interest rate	2.10%				2.10%
Cash Flow Hedging | Minimum | Interest Rate Swap | Designated as Hedging Instrument | MexMar
Derivative [Line Items]
Derivative, fixed interest rate	1.71%				1.71%
Derivative Liabilities | Fair Value Hedging
Derivative [Line Items]
Recognized gain (loss) on hedged item in fair value hedge	$ (900)

Derivative Instruments and He_5

Derivative Instruments and Hedging Strategies - Effect of Derivative Instruments on Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Derivative losses on cash flow hedges	$ (2,139)	$ (1,901)	$ (1,939)
Interest Rate Swap
Derivative losses on cash flow hedges	(2,139)	(1,901)	(1,939)
Joint Venture Interest Rate Swap
Derivative losses on cash flow hedges	(156)	(645)	(76)
Interest Expense
Reclassification of derivative losses on cash flow hedges	$ 1,425	$ 552	$ 31

Derivative Instruments and He_6

Derivative Instruments and Hedging Strategies - Gains (Losses) on Derivative Instruments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Gains (losses) on derivative instruments	$ 4,310	$ 71	$ 2,854
Embedded Derivative Financial Instruments
Gains (losses) on derivative instruments	5,203	$ 71	1,556
Interest Rate Swap
Gains (losses) on derivative instruments			$ 1,298
Foreign Exchange Option
Gains (losses) on derivative instruments	$ (893)

Fair Value Measurements - Sched

Fair Value Measurements - Schedule of Fair Value of Assets and Liabilities Measured on Recurring Basis (Details) - Fair Value, Measurements, Recurring - USD ($) $ in Thousands		Dec. 31, 2020	Dec. 31, 2019
Fair Value, Inputs, Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Construction reserve funds			$ 12,893
Fair Value, Inputs, Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative Liability		$ 4,591	2,925
Fair Value, Inputs, Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Conversion Option Liability on Convertible Senior Notes	[1]	$ 2	$ 5,205
[1]	For the year ended December 31, 2020, the Company recognized a $5.2 million gain in the fair market valuation of the Conversion Option on the Convertible Senior Notes, as valued by an independent third-party

Fair Value Measurements - Sch_2

Fair Value Measurements - Schedule of Fair Value of Assets and Liabilities Measured on Recurring Basis (Details) (Parenthetical) $ in Millions	12 Months Ended
	Dec. 31, 2020USD ($)
Fair Value Disclosures [Abstract]
Derivative, gain (loss) on derivative, net, total	$ 5.2

Fair Value Measurements - Sch_3

Fair Value Measurements - Schedule of Estimated Fair Values of Financial Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Reported Value Measurement
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash, cash equivalents and restricted cash	$ 36,018	$ 84,486
Investments, at cost, in 50% or less owned companies (included in other assets)	132	132
Long-term debt, including current portion	472,887	373,516
Estimate of Fair Value Measurement | Fair Value, Inputs, Level 1
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash, cash equivalents and restricted cash	36,018	84,486
Estimate of Fair Value Measurement | Fair Value, Inputs, Level 2
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Long-term debt, including current portion	$ 470,561	$ 356,086

Fair Value Measurements - Sch_4

Fair Value Measurements - Schedule of Other Assets and Liabilities Measured at Fair Value (Details) - Fair Value, Inputs, Level 2 - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Fast Support Vessels
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Property and equipment		$ 1,858
Liftboats
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Property and equipment	$ 43,005
Anchor Handling Towing Supply
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Property and equipment		$ 520

Fair Value Measurements - Addit

Fair Value Measurements - Additional Information (Details)	12 Months Ended
	Dec. 31, 2020USD ($)Investment	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Impairment charges	$ 18,800,000	$ 12,000,000	$ 14,600,000
Number of marked investments, at equity, in 50% or less owned companies | Investment	2
Investments, at equity, in 50% or less owned companies	$ 75,308,000	$ 120,831,000
Seabulk Tims I and Offshore Vessel Holdings
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Investments, at equity, in 50% or less owned companies	$ 0

Warrants - Additional Informati

Warrants - Additional Information (Details) - $ / shares	Sep. 18, 2020	Sep. 01, 2020	Jun. 14, 2019	Jun. 08, 2019	May 28, 2019	Dec. 31, 2020	Dec. 31, 2019
Class Of Warrant Or Right [Line Items]
Class of warrant or right, exercised during period	83,367	255,307	64,440	64,440	380,000
Class of warrant or right, outstanding						1,488,292	1,826,966
Number of shares withheld in an exercise to purchase warrants as payment for the exercise	354		49
Warrants Transactions
Class Of Warrant Or Right [Line Items]
Class of warrant or right, exercise price per share						$ 0.01
Class of warrant or right, number of securities called by warrants or rights						2,560,456
Class of warrant or right, outstanding						1,488,292

Stockholders' Equity - Addition

Stockholders' Equity - Additional Information (Details) € in Millions, £ in Millions	Sep. 18, 2020shares	Sep. 01, 2020shares	Mar. 20, 2020shares	Jun. 14, 2019shares	Jun. 08, 2019shares	May 28, 2019shares	Mar. 15, 2019USD ($)shares	Mar. 15, 2019EUR (€)shares	Jan. 25, 2019USD ($)	Jan. 25, 2019GBP (£)	Jan. 09, 2019USD ($)Vesselshares	Apr. 30, 2018shares	Dec. 31, 2020USD ($)shares		Dec. 31, 2019USD ($)shares		Dec. 31, 2018USD ($)		Jun. 09, 2020shares	Jan. 01, 2019USD ($)	Dec. 31, 2017USD ($)
Class Of Stock [Line Items]
Class of warrant or right, exercised during period	83,367	255,307		64,440	64,440	380,000
Class of warrant or right, outstanding													1,488,292		1,826,966
Number of shares withheld in an exercise to purchase warrants as payment for the exercise	354			49
Acquired													4	[1]	4	[2]	11	[2]
Common stock value | $													$ 235,000		$ 219,000
Cumulative Effect of New Accounting Principle in Period of Adoption | $													401,836,000		478,924,000		$ 565,351,000				$ 511,097,000
Retained Earnings [Member]
Class Of Stock [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption | $													$ (51,839,000)		$ 27,076,000		$ 137,250,000				$ 204,442,000
Retained Earnings [Member] | Accounting Standards Update 2016-02 | Cumulative Effect, Period of Adoption, Adjustment
Class Of Stock [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption | $																				$ 10,400,000
Private Placement
Class Of Stock [Line Items]
Stock Issued During Period, Shares, New Issues											603,872	750,000
Acquired | Vessel											3
Common stock value | $											$ 7,800
Windcat Workboats Facilities | Seabulk Overseas
Class Of Stock [Line Items]
Business acquisition, percentage of voting interests acquired							6.25%	6.25%	6.25%	6.25%			100.00%
Business acquisition, exchange for consideration							50,000	50,000
Business combination, consideration transferred, total							$ 1,400,000	€ 1.2	$ 2,000,000	£ 1.6
Falcon Global Holdings
Class Of Stock [Line Items]
Business acquisition, percentage of voting interests acquired			28.00%
Business acquisition, exchange for consideration			900,000
Ownership percentage by parent			100.00%
2017 Equity Incentive Plan
Class Of Stock [Line Items]
Common shares registered for issuance													2,174,000
Common shares remaining available for issuance																			24,821
2020 Equity Incentive Plan
Class Of Stock [Line Items]
Common shares registered for issuance																			2,114,821
Common shares authorized for issuance																			2,080,000
Common shares remaining available for issuance																			1,928,832
Exchange Warrants
Class Of Stock [Line Items]
Class of warrant or right, outstanding													1,488,292
Number of shares withheld in an exercise to purchase warrants as payment for the exercise	354			49
[1]	Excludes three CTVs as assets held for sale and seven PSVs acquired as part of the SEACOSCO Acquisition (See “Note 3. Business Acquisitions”).
[2]	Ex cludes two CTVs as assets held for sale.

Noncontrolling Interests in S_3

Noncontrolling Interests in Subsidiaries - Schedule of Noncontrolling Interests in the Company's Consolidated Subsidiaries (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Mar. 19, 2020	Dec. 31, 2019
Minority Interest [Line Items]
Noncontrolling interest	$ 319		$ 21,432
Falcon Global
Minority Interest [Line Items]
Noncontrolling interest, ownership percentage by noncontrolling owners		28.00%
Noncontrolling interest			21,119
Other Noncontrolling Interests
Minority Interest [Line Items]
Noncontrolling interest, ownership percentage by noncontrolling owners	1.80%
Noncontrolling interest	$ 319		$ 313

Noncontrolling Interests in S_4

Noncontrolling Interests in Subsidiaries - Schedule of Noncontrolling Interests in the Company's Consolidated Subsidiaries (Parenthetical) (Details)	Mar. 19, 2020
Falcon Global
Minority Interest [Line Items]
Noncontrolling interest, ownership percentage by noncontrolling owners	28.00%

Noncontrolling Interests in S_5

Noncontrolling Interests in Subsidiaries - Additional Information (Details) - USD ($) $ in Thousands	Mar. 20, 2020	Mar. 19, 2020	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Minority Interest [Line Items]
Net income (loss), including portion attributable to noncontrolling interest, total			$ (38,847)	$ (18,077)	$ (6,066)	$ (19,992)	$ (21,918)	$ (18,240)	$ (30,264)	$ (28,273)	$ (82,982)	$ (98,695)	$ (82,052)
Net income (loss) attributable to noncontrolling interest, total											$ (4,067)	$ (5,858)	$ (4,444)
Falcon Global Holdings
Minority Interest [Line Items]
Business acquisition, percentage of voting interests acquired	28.00%
Business acquisition, exchange for consideration	900,000
Noncontrolling Interest, ownership percentage by parent	28.00%	72.00%
Net income (loss), including portion attributable to noncontrolling interest, total		$ 16,600
Net income (loss) attributable to noncontrolling interest, total		$ 4,600
Falcon Global Holdings
Minority Interest [Line Items]
Business acquisition, percentage of voting interests acquired	100.00%
Falcon Global Holdings | Common Stock
Minority Interest [Line Items]
Business acquisition, exchange for consideration	900,000

Savings and Multi-employer Pe_2

Savings and Multi-employer Pension Plans - Additional Information (Details) € in Millions, £ in Millions, $ in Millions	Jan. 01, 2019	Jun. 30, 2018USD ($)	Jun. 30, 2018EUR (€)	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2014USD ($)	Nov. 07, 2018GBP (£)	Dec. 31, 2015USD ($)	Dec. 31, 2013USD ($)
Pension And Other Postretirement Benefits Disclosure [Line Items]
Defined contribution plan, employer matching contribution, percent of employees' gross pay	1.00%			2.00%
Defined Contribution Plan, Maximum Annual Contributions Per Employee, Amount				$ 0.3	$ 0.2
Other Defined Contribution Plan
Pension And Other Postretirement Benefits Disclosure [Line Items]
Defined contribution plan, cost				$ 0.4	$ 0.3	$ 0.2
United Kingdom Merchant Navy Officers Pension Fund | Foreign Pension Plan
Pension And Other Postretirement Benefits Disclosure [Line Items]
Pension and other postretirement benefits cost (reversal of cost), total							$ 19.4
Pension and other postretirement benefits invoice										$ 2.6
Pension and other post-retirement benefit plans, total funding deficit | £								£ 9
Merchant Navy Ratings Pension Fund
Pension And Other Postretirement Benefits Disclosure [Line Items]
Multiemployer plan, contributions by employer		$ 1.2	€ 0.9
Merchant Navy Ratings Pension Fund | Foreign Pension Plan
Pension And Other Postretirement Benefits Disclosure [Line Items]
Pension and other post-retirement benefit plans, total funding deficit									$ 6.9

Share Based Compensation - Addi

Share Based Compensation - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jun. 09, 2020
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Payments for distribution of restricted stock, spin-off				$ 2,700
Allocated share-based compensation expense, total	$ 4,800
Employee service share-based compensation, nonvested awards, compensation cost not yet recognized, total	$ 4,700	$ 6,500	$ 6,800
Share-based compensation arrangement by share-based payment award, fair value assumptions, expected dividend rate	0.00%	0.00%
Share-based compensation arrangement by share-based payment award, fair value assumptions, expected volatility rate	76.10%	51.10%
Share-based compensation arrangement by share-based payment award, fair value assumptions, discount for postvesting restrictions	0.52%	2.10%
Share-based compensation arrangement by share-based payment award, fair value assumptions, expected term	9 years 11 months 1 day	9 years 9 months
Share-based compensation arrangement by share-based payment award, options, exercises in period, intrinsic value	$ 1,600
Exercise of options (in shares)	0	113,750
Share-based compensation arrangement by share-based payment award, options, outstanding, intrinsic value	$ 0
Restricted Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Distribution of restricted stock in connection with spin-off				120,693
Employee service share-based compensation, nonvested awards, compensation cost not yet recognized, period for recognition	1 year 3 months
Share-based compensation arrangement by share-based payment award, equity instruments other than options, grants in period, weighted average grant date fair value	$ 6.81
Employee Stock Option
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Employee service share-based compensation, nonvested awards, compensation cost not yet recognized, period for recognition	10 months 20 days
2017 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation arrangement by share-based payment award, number of shares authorized	2,174,000
Share-based compensation arrangement by share-based payment award, number of shares available for grant	24,821
Percentage of number of common stock shares outstanding	10.00%
Allocated share-based compensation expense, total		$ 5,300	$ 4,400
2017 Equity Incentive Plan | Restricted Stock | Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation arrangement by share-based payment award, award vesting period		1 year
2017 Equity Incentive Plan | Restricted Stock | Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation arrangement by share-based payment award, award vesting period		4 years
2017 Equity Incentive Plan | Employee Stock Option | Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation arrangement by share-based payment award, award vesting period		1 year
2017 Equity Incentive Plan | Employee Stock Option | Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation arrangement by share-based payment award, award vesting period		4 years
2020 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation arrangement by share-based payment award, number of shares authorized					2,080,000
Share-based compensation arrangement by share-based payment award, number of shares available for grant					1,928,832
Common shares registered for issuance					2,114,821
Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation arrangement by share-based payment award, number of shares authorized		300,000
Share-based compensation arrangement by share-based payment award, discount from market price, purchase date				85.00%
Period of common stock reserved for issuance		10 years
2017 Plan and 2020 Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation arrangement by share-based payment award, options, outstanding, exercise price, ending balance	$ 3.60	$ 8.73
2017 Plan and 2020 Plan | Restricted Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation arrangement by share-based payment award, equity instruments other than options, grants in period, weighted average grant date fair value	$ 6.40	$ 13.28

Share Based Compensation - Sche

Share Based Compensation - Schedule of Equity Incentive Plan Transactions (Details) - shares	12 Months Ended
	Dec. 31, 2020		Dec. 31, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Outstanding as of the beginning of year (in shares)	913,569		805,566
Granted (in shares)	261,972		230,503
Exercised (in shares)	0		113,750
Forfeited (in shares)	55,000		8,750
Outstanding as of the end of year (in shares)	1,120,541		913,569
Director Stock Awards
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Granted (in shares)	59,900		30,197
Restricted Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Outstanding as of the beginning of year (in shares)	303,609		192,346
Granted (in shares)	289,452	[1]	245,400
Vested (in shares)	143,697		131,937
Forfeited (in shares)	12,650		2,200
Outstanding as of the end of year (in shares)	436,714		303,609
[1]	Excludes 240,800 grants of performance-based stock units that are not considered outstanding until such time that they become probable to vest.

Share Based Compensation - Sc_2

Share Based Compensation - Schedule of Equity Incentive Plan Transactions (Details) (Parenthetical)	Dec. 31, 2020shares
Performance Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares outstanding	240,800

Share Based Compensation - Sc_3

Share Based Compensation - Schedule of Restricted Stock Transactions (Details) - Restricted Stock - $ / shares	12 Months Ended
	Dec. 31, 2020		Dec. 31, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Outstanding as of the beginning of year (in shares)	303,609		192,346
Non-Vested, weight average grant price (in dollars per share)	$ 20.46
Granted (in shares)	289,452	[1]	245,400
Granted, weight average grant price (in dollars per share)	$ 6.81
Vested, shares (in shares)	143,697		131,937
Vested, weight average grant price (in dollars per share)	$ 13.43
Forfeited (in shares)	12,650		2,200
Forfeited, weight average grant price (in dollars per share)	$ 12.30
Outstanding as of the end of year (in shares)	436,714		303,609
Non-Vested, weight average grant price (in dollars per share)	$ 11.60		$ 20.46
[1]	Excludes 240,800 grants of performance-based stock units that are not considered outstanding until such time that they become probable to vest.

Share Based Compensation - Sc_4

Share Based Compensation - Schedule of Stock Option Transactions (Details) - $ / shares		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Non-Vested, shares (in shares)		913,569
Non-Vested, weight average grant price (in dollars per share)		$ 14.81
Granted, shares (in shares)		261,972	230,503
Granted, weight average grant price (in dollars per share)		$ 3.68
Exercise of options (in shares)		0	113,750
Forfeited, shares (in shares)		55,000
Forfeited, weight average grant price (in dollars per share)		$ 13.43
Non-Vested, shares (in shares)		1,120,541	913,569
Non-Vested, weight average grant price (in dollars per share)		$ 12.49	$ 14.81
Exercisable, shares (in shares)	[1]	716,965
Exercisable, weight average grant price (in dollars per share)		$ 13.03
[1]	The weighted average remaining contractual term is 8.18 years.

Share Based Compensation - Sc_5

Share Based Compensation - Schedule of Stock Option Transactions (Details) (Parenthetical)	12 Months Ended
	Dec. 31, 2020
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Share-based compensation arrangement by share-based payment award, options, exercisable, weighted average remaining contractual term	8 years 2 months 4 days

Related Party Transactions - Ad

Related Party Transactions - Additional Information (Details) $ / shares in Units, € in Millions, £ in Millions		Sep. 18, 2020shares	Sep. 01, 2020shares	Jun. 26, 2020USD ($)	Jun. 14, 2019shares	Jun. 08, 2019shares	May 28, 2019shares	Mar. 15, 2019USD ($)shares	Mar. 15, 2019EUR (€)shares	Jan. 25, 2019USD ($)	Jan. 25, 2019GBP (£)	Jan. 09, 2019shares	Dec. 20, 2018USD ($)	Sep. 28, 2018USD ($)	May 02, 2018USD ($)$ / sharesshares	Dec. 01, 2015USD ($)	Jul. 31, 2020USD ($)	Apr. 30, 2018USD ($)$ / sharesshares	Dec. 31, 2020USD ($)shares	Sep. 30, 2020USD ($)	Jun. 30, 2020USD ($)	Mar. 31, 2020USD ($)	Dec. 31, 2019USD ($)shares	Sep. 30, 2019USD ($)	Jun. 30, 2019USD ($)	Mar. 31, 2019USD ($)	Dec. 31, 2020USD ($)shares	Dec. 31, 2019USD ($)shares	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Jan. 12, 2021	Dec. 28, 2018
Related Party Transaction [Line Items]
Related Party Transaction, Rate																											0.50%
Interest Expense, Related Party																											$ 100,000	$ 200,000	$ 300,000
Equity method investment, ownership percentage													49.00%
Class of warrant or right, outstanding | shares																			1,488,292				1,826,966				1,488,292	1,826,966
Issuance of Common Stock																												$ 6,596,000	42,996,000
Class of warrant or right, exercised during period | shares		83,367	255,307		64,440	64,440	380,000
Indebtedness													$ 95,000,000
Contributed capital													$ 10,000,000
Revenues																			$ 36,044,000	$ 36,201,000	$ 33,925,000	$ 35,667,000	$ 42,478,000	$ 46,996,000	$ 45,014,000	$ 39,965,000	$ 141,837,000	174,453,000	$ 179,161,000
Mexmar Offshore International
Related Party Transaction [Line Items]
Equity method investment, ownership percentage													49.00%
Noncontrolling interest, ownership percentage by noncontrolling owners													51.00%
Offshore Vessel Holdings
Related Party Transaction [Line Items]
Noncontrolling interest, ownership percentage by noncontrolling owners																																51.00%
Contributed capital																												10,000,000
Financing agreement																												$ 2,400,000
Private Placement
Related Party Transaction [Line Items]
Issuance of Common Stock (in shares) | shares												603,872						750,000
Issuance of Common Stock																		$ 15,000,000
Warrants Issued In Private Placement
Related Party Transaction [Line Items]
Class of warrant or right, exercise price of warrants or rights | $ / shares																		$ 0.01
Class of warrant or right, outstanding | shares																		2,168,586
Class of warrant or right, number of securities called by warrants or rights | shares																		674,164
Convertible Senior Notes 3.75%
Related Party Transaction [Line Items]
Convertible debt, total															$ 125,000,000	$ 175,000,000		$ 125,000,000
Debt instrument, convertible, conversion ratio																													23.26
Debt instrument, face amount																													$ 1,000
Debt instrument, interest rate															4.25%	3.75%		4.25%
Lender Non Recourse
Related Party Transaction [Line Items]
Indebtedness													$ 70,000,000
Carlyle Group
Related Party Transaction [Line Items]
Convertible debt, total																$ 175,000,000
Interest rate term																											Interest on the Convertible Notes is payable semi-annually on June 15 and December 15 of each year, commencing June 15, 2016
Debt instrument, convertible, terms of conversion feature																											Carlyle has not exercised this right subsequent to Mr. Hussein’s resignation but retains the right to appoint a member to the Board of Directors. Mr. Hussein has been designated by Carlyle to observe meetings of the Board of Directors pursuant to Carlyle’s observer rights under the Convertible Notes. This observation right will terminate at the time Carlyle owns less than $50.0 million in aggregate principal amount of the Convertible Notes or a combination of the Convertible Notes and our Common Stock representing less than 5.0% of the Company’s Common Stock outstanding on a fully diluted basis, assuming the conversion of all of the Convertible Notes and Warrants to purchase Common Stock held by Carlyle.
Class of warrant or right, outstanding | shares																			1,488,292								1,488,292
Class of warrant or right, exercised during period | shares																											83,367	64,440
Carlyle Group | Convertible Senior Notes Converted to Warrants
Related Party Transaction [Line Items]
Debt conversion, original debt, amount															$ 50,000,000			$ 50,000,000
Class of warrant or right, exercise price of warrants or rights | $ / shares															$ 0.01			$ 0.01
Debt instrument, convertible, conversion ratio															37.73			37.73
Debt instrument, face amount															$ 1,000			$ 1,000
Debt instrument, convertible, conversion price | $ / shares															$ 26.50			$ 26.50
Debt conversion, converted instrument, shares issued | shares															1,886,792			1,900,000
Talos Energy, Inc
Related Party Transaction [Line Items]
Revenues																											$ 1,500,000	$ 3,200,000	2,900,000
Windcat Workboats Facilities | CMB N.V. | Subsequent Event
Related Party Transaction [Line Items]
Percentage sale of equity																															100.00%
Windcat Workboats Facilities | Seabulk Overseas
Related Party Transaction [Line Items]
Equity Method Investment Ownership Percentage								6.25%	6.25%	6.25%	6.25%								100.00%								100.00%
Ownership Percentage										100.00%	100.00%
Business combination, consideration transferred, total								$ 1,400,000	€ 1.2	$ 2,000,000	£ 1.6
Business acquisition, exchange for consideration | shares								50,000	50,000
Limited Partner
Related Party Transaction [Line Items]
Equity method investment, ownership percentage																			29.70%								29.70%
General Partner
Related Party Transaction [Line Items]
Equity method investment, ownership percentage																			66.70%								66.70%
OSV Partners
Related Party Transaction [Line Items]
Proceeds from Sale of Interest in Partnership Unit																													7,500,000
Equity method investment, ownership percentage	[1]																		30.40%								30.40%
Contributed capital														$ 5,000,000
OSV Partners | Limited Partner | Gellert
Related Party Transaction [Line Items]
Limited Partners' Capital Account, Total																			$ 400,000								$ 400,000
OSV Partners | General Partner
Related Party Transaction [Line Items]
Equity method investment, ownership percentage																			38.60%								38.60%
OSV Partners | Second Lien Debt
Related Party Transaction [Line Items]
Proceeds from issuance of debt																													5,000,000
Equity method investment, ownership percentage																			43.00%								43.00%
OSV Partners | Series A Preferred Stock
Related Party Transaction [Line Items]
Proceeds from Issuance of Redeemable Preferred Stock																													2,500,000
Proceeds From issuance of additional redeemable preferred stock																													2,500,000
Equity method investment, ownership percentage																			43.00%								43.00%
CME
Related Party Transaction [Line Items]
Class of warrant or right, exercised during period | shares																											255,307	380,000
Contributed capital													5,000,000
MexMar
Related Party Transaction [Line Items]
Equity method investment, ownership percentage																			49.00%								49.00%
Indebtedness													15,000,000
MEXMAR Offshore
Related Party Transaction [Line Items]
Equity method investment, ownership percentage	[2]																		49.00%								49.00%
Indebtedness													10,000,000
Contributed capital													$ 5,000,000
MEXMAR Offshore | BRAZIL
Related Party Transaction [Line Items]
Aggregate purchase price																							$ 0					$ 0
Long-term debt, total																	$ 70,000,000
Commitment to fund purchase																	2,700,000
Loaned commitment amount																			$ 1,960,000								$ 1,960,000
MEXMAR Offshore | UP Offshore’s. | BRAZIL
Related Party Transaction [Line Items]
Long-term debt, total																	$ 5,500,000
Maximum
Related Party Transaction [Line Items]
Equity method investment, ownership percentage																			50.00%				50.00%				50.00%	50.00%
Maximum | Carlyle Group
Related Party Transaction [Line Items]
Convertible debt, total																														$ 50,000,000
Percentage of convertible notes converted into common stock																														5
Minimum
Related Party Transaction [Line Items]
Equity method investment, ownership percentage																			20.00%								20.00%
Minimum | Carlyle Group
Related Party Transaction [Line Items]
Percentage of convertible notes converted into common stock																10
Transition Services Agreement
Related Party Transaction [Line Items]
Related Party Transaction, Amounts of Transaction																											$ 0	$ 600,000	4,500,000
Transition Services Agreement | Maximum
Related Party Transaction [Line Items]
Related Party Transaction, Amounts of Transaction																												6,300,000
Tax Refund Agreement
Related Party Transaction [Line Items]
Expected to cash tax refunds receivable				$ 31,200,000
Percentage of net operating losses facilitate tax savings				35.00%
Transaction fee				$ 3,000,000
Cash tax refunds receivable without restrict to use																											23,100,000
Cash tax refunds receivable with restrict to use																											8,100,000
Tax refunds restricted cash																			$ 7,000,000								7,000,000
SEACOR Holdings
Related Party Transaction [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted																			8,100,000				$ 22,800,000				8,100,000	$ 22,800,000	$ 40,600,000
SEACOR Holdings | Tax Refund Agreement
Related Party Transaction [Line Items]
Cash tax refunds receivable without restrict to use																											23,100,000
Cash tax refunds receivable with restrict to use																											8,100,000
Officer | OSV Partners | Limited Partner | Fabrikant
Related Party Transaction [Line Items]
Limited Partners' Capital Account, Total																			300,000								300,000
Officer | OSV Partners | Limited Partner | Llorca
Related Party Transaction [Line Items]
Limited Partners' Capital Account, Total																			$ 200,000								$ 200,000
Officer | OSV Partners | Limited Partner | Fabrikant, Gellert and Llorca
Related Party Transaction [Line Items]
Equity method investment, ownership percentage																			39.60%								39.60%
Officer | OSV Partners | Second Lien Debt | General Partner
Related Party Transaction [Line Items]
Equity method investment, ownership percentage																			3.90%								3.90%
General Partners' Capital Account, Total																			$ 200,000								$ 200,000
Officer | OSV Partners | Series A Preferred Stock | General Partner
Related Party Transaction [Line Items]
Equity method investment, ownership percentage																			3.90%								3.90%
General Partners' Capital Account, Total																			$ 200,000								$ 200,000
Officer | Maximum | OSV Partners
Related Party Transaction [Line Items]
Limited Partners' Capital Account, Total																			$ 1,500,000								$ 1,500,000
Officer | Maximum | OSV Partners | Limited Partner
Related Party Transaction [Line Items]
Equity method investment, ownership percentage																			3.90%								3.90%
Officer | Maximum | OSV Partners | General Partner
Related Party Transaction [Line Items]
Equity method investment, ownership percentage																			5.00%								5.00%
General Partners' Capital Account, Total																			$ 300,000								$ 300,000
[1]	The Company owns 66.7 % of the General Partner and 29.7 % of the limited Partner .
[2]	This Joint Venture holds the investment in UP Offshore .

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Details) R$ in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2020USD ($)	Dec. 31, 2020BRL (R$)
Commitments And Contingencies [Line Items]
Unrecorded unconditional purchase obligation, total	$ 11.7
Unrecorded unconditional purchase obligation, due within one years	10.7
Unrecorded unconditional purchase obligation, due within two years	1
Unrecorded unconditional purchase obligation due within four years	$ 9.6
Deficiency Notice
Commitments And Contingencies [Line Items]
Cost allocation percentage	70.00%
Deficiency Notice | Seabulk Overseas
Commitments And Contingencies [Line Items]
Cost allocation percentage	30.00%
Minimum | Deficiency Notice
Commitments And Contingencies [Line Items]
Potential range of levies	$ 3.5	R$ 18120
Maximum | Deficiency Notice
Commitments And Contingencies [Line Items]
Potential range of levies	$ 2.5	R$ 12870
Platform Supply Vessels
Commitments And Contingencies [Line Items]
Unrecorded unconditional purchase obligation, maximum quantity	1	1
FSV Offshore Support Vessels
Commitments And Contingencies [Line Items]
Unrecorded unconditional purchase obligation, maximum quantity	1	1

Major Customers and Segment I_3

Major Customers and Segment Information - Additional Information (Details) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020USD ($)Customer	Sep. 30, 2020USD ($)	Jun. 30, 2020USD ($)	Mar. 31, 2020USD ($)	Dec. 31, 2019USD ($)	Sep. 30, 2019USD ($)	Jun. 30, 2019USD ($)	Mar. 31, 2019USD ($)	Dec. 31, 2020USD ($)Customer	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)
Segment Reporting Information [Line Items]
Revenue from contract with customer, including assessed tax	$ 36,044	$ 36,201	$ 33,925	$ 35,667	$ 42,478	$ 46,996	$ 45,014	$ 39,965	$ 141,837	$ 174,453	$ 179,161
Income (loss) from equity method investments									$ (8,163)	(14,459)	(4,009)
Customer Concentration Risk | Sales Revenue, Net | Seacor Marine Arabia LLC
Segment Reporting Information [Line Items]
Revenue from contract with customer, including assessed tax										$ 30,800	$ 21,400
Concentration risk, percentage										17.00%	12.00%
Customer Concentration Risk | Sales Revenue, Net | Ten Largest Customers
Segment Reporting Information [Line Items]
Concentration risk, percentage									76.00%	61.00%	57.00%
Geographic Concentration Risk | Sales Revenue, Net
Segment Reporting Information [Line Items]
Number of customer | Customer	2								2
Geographic Concentration Risk | Sales Revenue, Net | Non-US
Segment Reporting Information [Line Items]
Income (loss) from equity method investments									$ (6,600)	$ (13,000)	$ (1,900)
Geographic Concentration Risk | Sales Revenue, Net | Zamil Offshore
Segment Reporting Information [Line Items]
Revenue from contract with customer, including assessed tax										$ 20,300	$ 12,200
Concentration risk, percentage										11.00%	7.00%
Geographic Concentration Risk | Sales Revenue, Net | Exxon Mobil
Segment Reporting Information [Line Items]
Revenue from contract with customer, including assessed tax									$ 24,800	$ 16,500	$ 3,100
Concentration risk, percentage									17.00%	9.00%	2.00%
Geographic Concentration Risk | Sales Revenue, Net | Saudi Aramco
Segment Reporting Information [Line Items]
Revenue from contract with customer, including assessed tax									$ 30,700	$ 10,500	$ 9,200
Concentration risk, percentage									21.00%	6.00%	5.00%
Geographic Concentration Risk | Stockholders' Equity | Non-US
Segment Reporting Information [Line Items]
Concentration risk, percentage									89.00%	75.00%	71.00%

Major Customers and Segment I_4

Major Customers and Segment Information - Schedule of Segment Reporting Information, by Segment (Details) - USD ($) $ in Thousands	3 Months Ended										12 Months Ended
	Dec. 31, 2020		Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019		Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020		Dec. 31, 2019		Dec. 31, 2018
Segment Reporting Information [Line Items]
Operating Revenues	$ 36,044		$ 36,201	$ 33,925	$ 35,667	$ 42,478		$ 46,996	$ 45,014	$ 39,965	$ 141,837		$ 174,453		$ 179,161
Direct Costs and Expenses											91,145		109,523		119,587
Direct Vessel (Loss) Profit											50,692		64,930		59,574
Administrative and general											40,051		39,791		41,616
Depreciation and amortization											57,167		57,166		61,419
Other Costs and Expenses											104,743		112,797		115,999
Losses on Asset Dispositions and Impairments, Net											(17,588)		(6,461)		(11,989)
Operating Loss	(16,915)		$ (13,179)	$ (17,824)	$ (23,721)	(10,555)		$ (5,566)	$ (18,591)	$ (19,616)	(71,639)		(54,328)		(68,414)
Historical cost	1,012,873	[1]				899,024	[1]				1,012,873	[1]	899,024	[1]	1,047,797
Accumulated depreciation	(291,538)					(308,917)					(291,538)		(308,917)		(418,340)
Property and equipment	721,335					590,107					721,335		590,107		629,457
Total Assets	861,806	[2]				817,926	[3]				861,806	[2]	817,926	[3]	861,618	[4]
Leased In Equipment
Segment Reporting Information [Line Items]
Operating expenses											7,525		15,840		12,964
Time Charter
Segment Reporting Information [Line Items]
Operating Revenues											133,454		157,052		150,064
Bareboat Charter
Segment Reporting Information [Line Items]
Operating Revenues											2,855		5,131		4,635
Other Marine Services
Segment Reporting Information [Line Items]
Operating Revenues											5,528		12,270		24,462
Personnel
Segment Reporting Information [Line Items]
Direct Costs and Expenses											48,348		55,975		58,532
Repairs and Maintenance
Segment Reporting Information [Line Items]
Direct Costs and Expenses											14,661		21,401		24,385
Drydocking
Segment Reporting Information [Line Items]
Direct Costs and Expenses											4,269		5,848		7,792
Insurance and Loss Reserves
Segment Reporting Information [Line Items]
Direct Costs and Expenses											5,763		5,622		5,970
Fuel, Lubes and Supplies
Segment Reporting Information [Line Items]
Direct Costs and Expenses											8,128		10,622		12,904
Other Direct Costs and Expenses
Segment Reporting Information [Line Items]
Direct Costs and Expenses											9,976		10,055		10,004
UNITED STATES
Segment Reporting Information [Line Items]
Operating Revenues											15,205		44,323		53,564
Direct Costs and Expenses											16,206		35,367		32,700
Direct Vessel (Loss) Profit											(1,001)		8,956		20,864
Depreciation and amortization											21,427		21,947		23,227
Historical cost	257,592					297,392					257,592		297,392		432,336
Accumulated depreciation	(134,391)					(157,514)					(134,391)		(157,514)		(224,737)
Property and equipment	123,201					139,878					123,201		139,878		207,599
Total Assets	164,656	[2]				224,229	[3]				164,656	[2]	224,229	[3]	351,748	[4]
UNITED STATES | Leased In Equipment
Segment Reporting Information [Line Items]
Operating expenses											4,272		10,894		8,240
UNITED STATES | Time Charter
Segment Reporting Information [Line Items]
Operating Revenues											9,873		38,955		38,802
UNITED STATES | Bareboat Charter
Segment Reporting Information [Line Items]
Operating Revenues											2,910		1,562
UNITED STATES | Other Marine Services
Segment Reporting Information [Line Items]
Operating Revenues											2,422		3,806		14,762
UNITED STATES | Personnel
Segment Reporting Information [Line Items]
Direct Costs and Expenses											10,065		17,491		18,708
UNITED STATES | Repairs and Maintenance
Segment Reporting Information [Line Items]
Direct Costs and Expenses											1,655		7,583		5,152
UNITED STATES | Drydocking
Segment Reporting Information [Line Items]
Direct Costs and Expenses											1,167		4,594		1,957
UNITED STATES | Insurance and Loss Reserves
Segment Reporting Information [Line Items]
Direct Costs and Expenses											1,774		2,370		2,922
UNITED STATES | Fuel, Lubes and Supplies
Segment Reporting Information [Line Items]
Direct Costs and Expenses											1,172		2,936		3,568
UNITED STATES | Other Direct Costs and Expenses
Segment Reporting Information [Line Items]
Direct Costs and Expenses											373		393		393
Africa
Segment Reporting Information [Line Items]
Operating Revenues											35,411		45,621		51,508
Direct Costs and Expenses											22,691		27,900		34,188
Direct Vessel (Loss) Profit											12,720		17,721		17,320
Depreciation and amortization											10,833		10,404		10,453
Historical cost	204,079					207,107					204,079		207,107		184,361
Accumulated depreciation	(60,535)					(57,136)					(60,535)		(57,136)		(55,206)
Property and equipment	143,544					149,971					143,544		149,971		129,155
Total Assets	153,399	[2]				161,915	[3]				153,399	[2]	161,915	[3]	140,335	[4]
Africa | Leased In Equipment
Segment Reporting Information [Line Items]
Operating expenses											3,029		3,090		4,281
Africa | Time Charter
Segment Reporting Information [Line Items]
Operating Revenues											35,876		44,160		43,847
Africa | Other Marine Services
Segment Reporting Information [Line Items]
Operating Revenues											(465)		1,461		7,661
Africa | Personnel
Segment Reporting Information [Line Items]
Direct Costs and Expenses											10,552		13,833		16,538
Africa | Repairs and Maintenance
Segment Reporting Information [Line Items]
Direct Costs and Expenses											5,175		4,701		6,330
Africa | Drydocking
Segment Reporting Information [Line Items]
Direct Costs and Expenses											2,014		490		2,085
Africa | Insurance and Loss Reserves
Segment Reporting Information [Line Items]
Direct Costs and Expenses											1,026		1,051		1,096
Africa | Fuel, Lubes and Supplies
Segment Reporting Information [Line Items]
Direct Costs and Expenses											2,940		3,471		3,826
Africa | Other Direct Costs and Expenses
Segment Reporting Information [Line Items]
Direct Costs and Expenses											984		4,354		4,313
Middle East and Asia
Segment Reporting Information [Line Items]
Operating Revenues											54,209		55,981		49,185
Direct Costs and Expenses											35,497		31,928		38,718
Direct Vessel (Loss) Profit											18,712		24,053		10,467
Depreciation and amortization											16,595		16,400		18,762
Historical cost	361,514					292,446					361,514		292,446		306,897
Accumulated depreciation	(75,349)					(73,039)					(75,349)		(73,039)		(81,378)
Property and equipment	286,165					219,407					286,165		219,407		225,519
Total Assets	289,314	[2]				250,890	[3]				289,314	[2]	250,890	[3]	260,002	[4]
Middle East and Asia | Leased In Equipment
Segment Reporting Information [Line Items]
Operating expenses											170		173		224
Middle East and Asia | Time Charter
Segment Reporting Information [Line Items]
Operating Revenues											52,052		54,312		50,072
Middle East and Asia | Other Marine Services
Segment Reporting Information [Line Items]
Operating Revenues											2,157		1,669		(887)
Middle East and Asia | Personnel
Segment Reporting Information [Line Items]
Direct Costs and Expenses											18,188		16,698		16,806
Middle East and Asia | Repairs and Maintenance
Segment Reporting Information [Line Items]
Direct Costs and Expenses											5,232		7,182		11,172
Middle East and Asia | Drydocking
Segment Reporting Information [Line Items]
Direct Costs and Expenses											759		600		1,362
Middle East and Asia | Insurance and Loss Reserves
Segment Reporting Information [Line Items]
Direct Costs and Expenses											1,721		1,449		1,371
Middle East and Asia | Fuel, Lubes and Supplies
Segment Reporting Information [Line Items]
Direct Costs and Expenses											2,706		2,904		4,027
Middle East and Asia | Other Direct Costs and Expenses
Segment Reporting Information [Line Items]
Direct Costs and Expenses											6,891		3,095		3,980
Latin America
Segment Reporting Information [Line Items]
Operating Revenues											24,890		16,419		23,532
Direct Costs and Expenses											11,979		8,517		8,388
Direct Vessel (Loss) Profit											12,911		7,902		15,144
Depreciation and amortization											5,481		6,205		7,908
Historical cost	130,769					57,534					130,769		57,534		124,177
Accumulated depreciation	(13,312)					(16,239)					(13,312)		(16,239)		(57,002)
Property and equipment	117,457					41,295					117,457		41,295		67,175
Total Assets	179,942	[2]				116,736	[3]				179,942	[2]	116,736	[3]	137,983	[4]
Latin America | Leased In Equipment
Segment Reporting Information [Line Items]
Operating expenses											45		10		5
Latin America | Time Charter
Segment Reporting Information [Line Items]
Operating Revenues											23,806		11,460		17,343
Latin America | Bareboat Charter
Segment Reporting Information [Line Items]
Operating Revenues													3,569		4,635
Latin America | Other Marine Services
Segment Reporting Information [Line Items]
Operating Revenues											1,084		1,390		1,554
Latin America | Personnel
Segment Reporting Information [Line Items]
Direct Costs and Expenses											6,698		4,459		4,399
Latin America | Repairs and Maintenance
Segment Reporting Information [Line Items]
Direct Costs and Expenses											2,131		1,348		1,011
Latin America | Drydocking
Segment Reporting Information [Line Items]
Direct Costs and Expenses											329		161		128
Latin America | Insurance and Loss Reserves
Segment Reporting Information [Line Items]
Direct Costs and Expenses											462		311		495
Latin America | Fuel, Lubes and Supplies
Segment Reporting Information [Line Items]
Direct Costs and Expenses											990		1,056		1,225
Latin America | Other Direct Costs and Expenses
Segment Reporting Information [Line Items]
Direct Costs and Expenses											1,369		1,182		1,130
Europe Continuing Operations
Segment Reporting Information [Line Items]
Operating Revenues											12,122		12,109		1,372
Direct Costs and Expenses											4,772		5,811		5,593
Direct Vessel (Loss) Profit											7,350		6,298		(4,221)
Depreciation and amortization											2,831		2,210		1,069
Historical cost	58,919					44,545					58,919		44,545		26
Accumulated depreciation	(7,951)					(4,989)					(7,951)		(4,989)		(17)
Property and equipment	50,968					39,556					50,968		39,556		9
Total Assets	$ 74,495	[2]				$ 64,156	[3]				74,495	[2]	64,156	[3]	(28,450)	[4]
Europe Continuing Operations | Leased In Equipment
Segment Reporting Information [Line Items]
Operating expenses											9		1,673		214
Europe Continuing Operations | Time Charter
Segment Reporting Information [Line Items]
Operating Revenues											11,847		8,165
Europe Continuing Operations | Bareboat Charter
Segment Reporting Information [Line Items]
Operating Revenues											(55)
Europe Continuing Operations | Other Marine Services
Segment Reporting Information [Line Items]
Operating Revenues											330		3,944		1,372
Europe Continuing Operations | Personnel
Segment Reporting Information [Line Items]
Direct Costs and Expenses											2,845		3,494		2,081
Europe Continuing Operations | Repairs and Maintenance
Segment Reporting Information [Line Items]
Direct Costs and Expenses											468		587		720
Europe Continuing Operations | Drydocking
Segment Reporting Information [Line Items]
Direct Costs and Expenses													3		2,260
Europe Continuing Operations | Insurance and Loss Reserves
Segment Reporting Information [Line Items]
Direct Costs and Expenses											780		441		86
Europe Continuing Operations | Fuel, Lubes and Supplies
Segment Reporting Information [Line Items]
Direct Costs and Expenses											320		255		258
Europe Continuing Operations | Other Direct Costs and Expenses
Segment Reporting Information [Line Items]
Direct Costs and Expenses											$ 359		$ 1,031		$ 188
[1]	Includes property and equipment acquired in business acquisitions at acquisition date fair value, and net of the impact of recognized impairment charges.
[2]	Total assets exclude $105.6 million of corporate assets, and $50.2 million of assets held for sale.
[3]	Total assets exclude $145.5 million of corporate assets, and $45.7 million of assets held-for-sale
[4]	Total assets exclude $153.1 million of corporate assets, and $88.2 million of assets held-for-sale.

Major Customers and Segment I_5

Major Customers and Segment Information - Schedule of Segment Reporting Information, by Segment (Parenthetical) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Segment Reporting Information [Line Items]
Assets, Total	$ 1,017,663	$ 1,009,193
Assets held for sale	50,200	45,700	$ 88,200
Corporate, Non-Segment
Segment Reporting Information [Line Items]
Assets, Total	$ 105,600	$ 145,500	$ 153,100

Discontinued Operations - Sched

Discontinued Operations - Schedule of Assets Held for Sale (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Assets from Discontinued Operations:
Current assets	$ 50,235	$ 45,718
Assets from discontinued operations	50,200	45,700	$ 88,200
Liability from Discontinued Operations:
Liabilities associated with assets held for sale	30,927	27,540
BPOS | Discontinued Operations, Held-for-sale
Assets from Discontinued Operations:
Current assets	10,138	9,603
Net property and equipment	34,580	31,447
Non-current assets	5,517	4,668
Assets from discontinued operations	50,235	45,718
Liability from Discontinued Operations:
Liabilities associated with assets held for sale	2,418	2,060
Long-term liabilities	28,509	25,480
Disposal Group, Including Discontinued Operation, Liabilities	30,927	27,540
Operating Revenues:
Operating Revenues		41,259
Costs and Expenses:
Operating		33,836
Direct Vessel Profit		7,423
General and Administrative Expenses		4,207
Lease Expense		60
Depreciation		3,504
Gains on Asset Dispositions and Impairments, Net		91
Operating Income (Loss)		(257)
Other Income (Expense)
Interest income		11
Interest expense		(210)
Foreign currency translation (loss) gain		(75)
Other Income (Expense)		(274)
Operating Income (Loss) Before Equity Earnings of 50% or Less Owned Companies, Net of Tax		(531)
Income Tax (Benefit) Expense		(2)
Operating Income (Loss) Before Equity Earnings of 50% or Less Owned Companies		(529)
Equity in Earnings of 50% or Less Owned Companies, Net of Tax		168
Net Income (Loss) from Discontinued Operations		(361)
BPOS | Discontinued Operations, Held-for-sale | Time Charter
Operating Revenues:
Operating Revenues		41,214
BPOS | Discontinued Operations, Held-for-sale | Other Revenue
Operating Revenues:
Operating Revenues		45
Windcat Workboats Holdings Ltd | Discontinued Operations, Held-for-sale
Operating Revenues:
Operating Revenues	31,688	27,039
Costs and Expenses:
Operating	17,334	14,202
Direct Vessel Profit	14,354	12,837
General and Administrative Expenses	5,516	4,935
Lease Expense	628	318
Depreciation	6,166	6,846
Gains on Asset Dispositions and Impairments, Net		1,064
Operating Income (Loss)	2,044	1,802
Other Income (Expense)
Interest income	59	56
Interest expense	(1,115)	(1,100)
Foreign currency translation (loss) gain	(750)	880
Other, net	19
Other Income (Expense)	(1,787)	(164)
Operating Income (Loss) Before Equity Earnings of 50% or Less Owned Companies, Net of Tax	257	1,638
Income Tax (Benefit) Expense	(86)	57
Operating Income (Loss) Before Equity Earnings of 50% or Less Owned Companies	343	1,581
Equity in Earnings of 50% or Less Owned Companies, Net of Tax	21	155
Net Income (Loss) from Discontinued Operations	364	1,736
Windcat Workboats Holdings Ltd | Discontinued Operations, Held-for-sale | Time Charter
Operating Revenues:
Operating Revenues	29,383	25,249
Windcat Workboats Holdings Ltd | Discontinued Operations, Held-for-sale | Other Revenue
Operating Revenues:
Operating Revenues	$ 2,305	$ 1,790

Quarterly Financial Informati_3

Quarterly Financial Information (Unaudited) - Selected Financial Information for Interim Quarterly Periods (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Operating Revenues	$ 36,044	$ 36,201	$ 33,925	$ 35,667	$ 42,478	$ 46,996	$ 45,014	$ 39,965	$ 141,837	$ 174,453	$ 179,161
Operating Loss	(16,915)	(13,179)	(17,824)	(23,721)	(10,555)	(5,566)	(18,591)	(19,616)	(71,639)	(54,328)	(68,414)
Net (Loss) Income:
Continuing Operations	(38,898)	(19,842)	(6,668)	(17,938)	(19,439)	(12,586)	(31,632)	(27,307)	(83,346)	(90,964)	(82,979)
Discontinued Operations	51	1,765	602	(2,054)	(2,479)	(5,654)	1,368	(966)
Net Loss	(38,847)	(18,077)	(6,066)	(19,992)	(21,918)	(18,240)	(30,264)	(28,273)	(82,982)	(98,695)	(82,052)
Net Loss attributable to SEACOR Marine Holdings Inc:	$ (38,816)	$ (18,081)	$ (6,073)	$ (15,945)	$ (20,455)	$ (18,444)	$ (28,389)	$ (25,549)	$ (78,915)	$ (92,837)	$ (77,608)
Basic and Diluted (Loss) Income Per Common Share of SEACOR Marine Holdings Inc.
Continuing operations	$ (1.54)	$ (0.79)	$ (0.26)	$ (0.58)	$ (0.76)	$ (0.54)	$ (1.27)	$ (1.07)	$ (3.20)	$ (3.62)	$ (3.74)
Discontinued operations		0.07	0.02	(0.08)	(0.10)	(0.24)	0.06	(0.04)	0.02	(0.33)	0.04
Basic and Diluted Income (Loss) Per Common Share and Warrants	$ (1.54)	$ (0.72)	$ (0.24)	$ (0.66)	$ (0.86)	$ (0.78)	$ (1.21)	$ (1.11)	$ (3.18)	$ (3.95)	$ (3.70)

Schedule II - Valuation and Q_3

Schedule II - Valuation and Qualifying Accounts - Schedule of Valuation and Qualifying Accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Valuation And Qualifying Accounts [Abstract]
Allowance for credit loss reserves (deducted from trade and notes receivable)	$ 455	$ 860	$ 4,039
Allowance for credit loss reserves (deducted from trade and notes receivable)	18
Allowance for credit loss reserves (deducted from trade and notes receivable)	230	(405)	(928)
Allowance for credit loss reserves (deducted from trade and notes receivable)	(121)		(2,251)
Allowance for credit loss reserves (deducted from trade and notes receivable)	$ 582	$ 455	$ 860