SEACOR Marine (SMHI) 10-K 22 Mar 18 2017 FY Annual report Financial data

Document And Entity Information

Document And Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2017	Mar. 20, 2018	Jun. 30, 2016
Document And Entity Information [Abstract]
Entity Registrant Name	SEACOR Marine Holdings Inc.
Entity Central Index Key	1,690,334
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Document Type	10-K
Document Period End Date	Dec. 31, 2017
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	FY
Amendment Flag	false
Entity Common Stock, Shares Outstanding		17,683,356
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Public Float			$ 332,370,118

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Current Assets:
Cash and cash equivalents	$ 110,234	$ 117,309
Restricted cash	2,317	1,462
Marketable securities	0	40,139
Receivables:
Trade, net of allowance for doubtful accounts of $4,039 and $5,359 in 2017 and 2016, respectively	45,616	44,830
Due from SEACOR Holdings	0	19,102
Other	12,341	21,316
Inventories	3,756	3,058
Prepaid expenses and other	3,026	3,349
Total current assets	177,290	250,565
Property and Equipment:
Historical cost	1,179,836	958,759
Accumulated depreciation	560,160	540,619
Property, Plant and Equipment, Net In Service	619,676	418,140
Construction in progress	70,157	123,801
Net property and equipment	689,833	541,941
Investments, at Equity, and Advances to 50% or Less Owned Companies	92,169	138,311
Construction Reserve Funds	45,361	78,209
Other Assets	3,851	6,093
Total Assets	1,008,504	1,015,119
Current Liabilities:
Current portion of long-term debt	22,858	20,400
Accounts payable and accrued expenses	24,024	25,969
Due to SEACOR Holdings	1,358	0
Accrued wages and benefits	5,087	4,862
Accrued income taxes	4,290	5,554
Accrued capital, repair and maintenance expenditures	19,618	8,573
Deferred revenues	10,104	6,953
Other current liabilities	11,879	8,705
Total current liabilities	99,218	81,016
Long-Term Debt	292,041	217,805
Exchange Option Liability on 3.75% Convertible Senior Notes	6,832	0
Deferred Income Taxes	55,506	124,945
Deferred Gains and Other Liabilities	31,741	41,198
Total liabilities	485,338	464,964
SEACOR Holdings Inc. stockholders’ equity:
Preferred stock, $.01 par value, 10,000,000 shares authorized; none issued nor outstanding	0	0
Common stock, $.01 par value, 60,000,000 shares authorized; 17,675,356 and 17,671,356 shares issued in 2017 and 2016, respectively	177	177
Additional paid-in capital	303,996	306,359
Retained earnings	216,511	249,412
Accumulated other comprehensive loss, net of tax	(12,493)	(11,337)
Stockholders' equity attributable to SEACOR Holdings Inc.	508,191	544,611
Noncontrolling interests in subsidiaries	14,975	5,544
Total equity	523,166	550,155
Liabilities and stockholders' equity, total	$ 1,008,504	$ 1,015,119

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Trade receivables, allowance for doubtful accounts	$ 4,038,925	$ 5,358,665.60
Common Stock, Par or Stated Value Per Share	$ 0.01	$ 0.01
Common stock, shares authorized	60,000,000	60,000,000
Common stock, shares issued	17,675,356	17,671,356
Treasury stock, shares	0	0
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0

Consolidated Statements Of Inco

Consolidated Statements Of Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Statement [Abstract]
Operating Revenues	$ 173,783	$ 215,636	$ 368,868
Costs and Expenses:
Operating	159,599	166,925	275,972
Administrative and general	56,217	49,308	53,085
Depreciation and amortization	62,779	58,069	61,729
Total costs and expenses	278,595	274,302	390,786
Losses on Asset Dispositions and Impairments, Net	(23,547)	(116,222)	(17,017)
Operating Loss	(128,359)	(174,888)	(38,935)
Other Income (Expense):
Interest income	1,805	4,458	836
Interest expense	(16,532)	(10,008)	(4,116)
Interest income on advances and notes with SEACOR Holdings, net	0	0	691
SEACOR Holdings management fees	(3,208)	(7,700)	(4,700)
SEACOR Holdings guarantee fees	(201)	(315)	0
Marketable security gains (losses), net	10,931	(45)	(3,820)
Derivative gains (losses), net	20,256	2,995	(2,766)
Foreign currency losses, net	(1,709)	(3,312)	(27)
Other, net	(6)	(1,490)	261
Nonoperating Income (Expense)	11,336	(15,417)	(13,641)
Loss Before Income Tax Benefit and Equity in Earnings (Losses) of 50% or Less Owned Companies	(117,023)	(190,305)	(52,576)
Income Tax Benefit:
Current	(13,400)	(15,421)	(487)
Deferred	(61,006)	(48,048)	(16,486)
Income Tax Benefit	(74,406)	(63,469)	(16,973)
Loss Before Equity in Earnings (Losses) of 50% or Less Owned Companies	(42,617)	(126,836)	(35,603)
Equity in Earnings (Losses) of 50% or Less Owned Companies	4,077	(6,314)	8,757
Net Loss	(38,540)	(133,150)	(26,846)
Net Income (Loss) Attributable to Noncontrolling Interests in Subsidiaries	(5,639)	(1,103)	403
Net Loss attributable to SEACOR Marine Holdings Inc.	$ (32,901)	$ (132,047)	$ (27,249)
Basic Loss Per Common Share of SEACOR Marine Holdings Inc.	$ (1.87)	$ (7.47)	$ (1.54)
Weighted Average Common Shares Outstanding:
Basic Weighted Average Common Shares Outstanding	17,601,244	17,671,356	17,671,356

Consolidated Statements Of Chan

Consolidated Statements Of Changes In Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-In Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Loss [Member]	Non-Controlling Interests In Subsidiaries [Member]
Total equity	$ 709,862	$ 0	$ 302,467	$ 402,190	$ (3,645)	$ 8,850
Formation of SEACOR Marine Holdings Inc.	6,900	177	(992)	7,715	0	0
Financial support received upon issuance of convertible senior notes, net of tax	5,532	0	(5,532)	0	0	0
Distributions to SEACOR Holdings:
Cash distributions	(1,845)	0	(648)	(1,197)	0	0
Dividends paid to noncontrolling interests	857	0	0	0	0	857
Comprehensive income:
Net Loss attributable to SEACOR Marine Holdings Inc.	(27,249)	0	0		0
Net Income (Loss) Attributable to Noncontrolling Interest	403
Net Loss	(26,846)
Other Comprehensive Income (Loss), Net of Tax	(2,892)	0	0	0	(2,450)	(442)
Total equity	689,854	177	306,359	381,459	(6,095)	7,954
Formation of SEACOR Marine Holdings Inc.	0
Cash distributions	0
Dividends paid to noncontrolling interests	205	0	0	0	0	205
Net Loss attributable to SEACOR Marine Holdings Inc.	(132,047)	0	0		0
Net Income (Loss) Attributable to Noncontrolling Interest	(1,103)
Net Loss	(133,150)
Other Comprehensive Income (Loss), Net of Tax	(6,344)	0	0	0	(5,242)	(1,102)
Total equity	550,155	177	306,359	249,412	(11,337)	5,544
Formation of SEACOR Marine Holdings Inc.	0
Cash distributions	0
Adjustments to Additional Paid in Capital, Other	(2,656)	0	(2,656)	0	0	0
Director stock awards	681	0	681	0	0	0
Adjustments to Additional Paid in Capital, Share-based Compensation, Requisite Service Period Recognition	(726)	0	726	0	0	0
Purchase of subsidiary shares from noncontrolling interests, net of tax	3,693	0	1,114	0	0	2,579
Net Loss attributable to SEACOR Marine Holdings Inc.	(32,901)	0	0		0
Net Income (Loss) Attributable to Noncontrolling Interest	(5,639)
Net Loss	(38,540)
Other Comprehensive Income (Loss), Net of Tax	(881)	0	0	0	(1,156)	275
Total equity	$ 523,166	$ 177	$ 303,996	$ 216,511	$ (12,493)	$ 14,975

Consolidated Statements Of Cash

Consolidated Statements Of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash Flows from Operating Activities:
Net Loss	$ (38,540)	$ (133,150)	$ (26,846)
Adjustments to reconcile income to net cash provided by (used in) operating activities:
Depreciation and amortization	62,779	58,069	61,729
Amortization of deferred gains on sale and leaseback transactions	8,118	8,199	8,199
Debt discount and issuance cost amortization, net	6,792	7,397	683
Director stock awards	681	0	0
Amortization of share awards	726	0	0
Bad debt expense (income)	(1,283)	4,280	0
Losses on Asset Dispositions and Impairments, Net	(23,547)	(116,222)	(17,017)
Marketable security (gains) losses, net	10,931	(45)	(3,820)
Purchases of marketable securities	0	22,997	36,648
Proceeds from sale of marketable securities	51,877	9,169	6,471
Derivative gains (losses), net	20,256	2,995	(2,766)
Cash settlements on derivative transactions, net	512	1,432	(1,256)
Foreign currency losses, net	(1,709)	(3,312)	(27)
Deferred income tax benefit	(61,006)	(48,048)	(16,486)
Other, net	0	1,484	0
Equity in (earnings) losses of 50% or less owned companies, net of tax	(4,077)	6,314	(8,757)
Dividends received from 50% or less owned companies	2,642	777	3,927
Changes in operating assets and liabilities:
Decrease in receivables	(28,937)	(5,637)	(39,872)
(Increase) decrease in prepaid expenses and other assets	(6,230)	18,086	(1,691)
Decrease in accounts payable, accrued expenses and other liabilities	(6,458)	(6,985)	(22,120)
Net cash provided by (used in) operating activities	34,739	(29,186)	20,203
Cash Flows from Investing Activities:
Purchases of property and equipment	69,021	100,884	87,765
Cash settlements on derivative transactions, net	369	373	0
Proceeds from disposition of property and equipment	10,843	41,919	15,698
Investments in and advances to 50% or less owned companies	5,469	16,863	24,976
Return of investments and advances of 50% or less owned companies	7,553	0	15,173
(Issuances of) payments received on third party leases and notes receivable, net	0	124	(13,150)
Net (increase) decrease in restricted cash	839	1,187	0
Net (increase) decrease in construction reserve funds	(32,848)	(60,406)	(6,817)
Cash assumed on consolidation of 50% or less owned companies	1,943	0	0
Business acquisitions, net of cash acquired	(9,751)	0	0
Net cash used in investing activities	(32,262)	(16,858)	(88,203)
Cash Flows from Financing Activities:
Payments on long-term debt and capital lease obligations	11,926	27,152	6,763
Proceeds from Issuance of long-term debt, net of offering costs	6,545	42,947	168,556
Payments on advances and notes with SEACOR Holdings, net	0	0	(50,890)
Distribution of SEACOR Marine restricted stock to Company personnel by SEACOR Holdings	(2,656)	0	0
Contributions from SEACOR Holdings	0	0	6,900
Distributions to SEACOR Holdings	0	0	(1,845)
Purchase of subsidiary shares from noncontrolling interests	3,693	0	0
Dividends paid to noncontrolling interests, net	0	(205)	(857)
Net cash provided by (used in) financing activities	(11,730)	15,590	115,101
Effects of Exchange Rate Changes on Cash and Cash Equivalents	2,178	(2,479)	(1,628)
Net Increase (Decrease) in Cash and Cash Equivalents	(7,075)	(32,933)	45,473
Cash and Cash Equivalents, Beginning of Year	117,309	150,242	104,769
Cash and Cash Equivalents, End of Year	$ 110,234	$ 117,309	$ 150,242

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income Statement - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Net Loss	$ (38,540)	$ (133,150)	$ (26,846)
Foreign currency translation gains (losses), net	4,654	(9,510)	(4,034)
Reclassification of foreign currency translation losses to foreign currency losses, net	0	74	21
Derivative (gains) losses on cash flow hedges		(2,493)
Other Comprehensive Income (Loss), before Tax	5,375	(9,167)	(4,211)
Income tax (expense) benefit	(6,256)	2,823	1,319
Other Comprehensive Loss, Net of Tax	(881)	(6,344)	(2,892)
Comprehensive Loss	(39,421)	(139,494)	(29,738)
Comprehensive Loss attributable to Noncontrolling Interests in Subsidiaries	(5,364)	(2,205)	(39)
Comprehensive Loss attributable to SEACOR Marine Holdings Inc.	(34,057)	(137,289)	(29,699)
Interest Expense [Member]
Reclassification of derivative losses on cash flow hedges	(118)	(18)	0
Equity Method Investments [Member]
Reclassification of derivative losses on cash flow hedges	$ 389	$ 2,744	$ 995

Nature Of Operations And Accoun

Nature Of Operations And Accounting Policies	12 Months Ended
	Dec. 31, 2017
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 Holdings Inc. (“SEACOR Marine”) and its consolidated subsidiaries (collectively referred to as the “Company”). The Company provides global marine and support transportation services to offshore oil and natural gas exploration, development and production 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. 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. The Company has identified the following five principal geographic regions as its reporting segments: United States, primarily Gulf of Mexico. The Company’s vessels in this market support deepwater anchor handling, fast cargo transport, general cargo transport, well intervention, work-over, decommissioning, and diving operations. Africa, primarily West Africa. The Company’s vessels in this area generally support projects for major oil companies, primarily in Angola. Other vessels in this region operate in the Republic of the Congo and Mauritania. Middle East and Asia. The Company’s vessels in this area generally support exploration, personnel transport and seasonal construction activities in Azerbaijan, Egypt, Israel, Indonesia, India and countries along the Arabian Gulf and Arabian Sea, such as Saudi Arabia, the United Arab Emirates and Qatar. Brazil, Mexico, Central and South America. Through the Company’s 49% noncontrolling interest in Mantenimiento Express Maritimo, S.A.P.I. de C.V. (“MexMar”), the Company’s vessels in Mexico provide support for exploration and production activities in Mexico. In addition, the Company has vessels in Brazil. From time to time, the Company’s vessels have worked in Trinidad and Tobago, Guyana, Colombia and Venezuela. Europe, primarily North Sea. Demand for standby services developed in 1991 after the United Kingdom passed legislation requiring offshore operators to maintain higher specification standby safety vessels. The legislation requires a vessel to “stand by” to provide a means of evacuation and rescue for platform and rig personnel in the event of an emergency at an offshore installation. In addition, through the Company’s 87.5% controlling interest in Windcat Workboats Holdings Limited (“Windcat Workboats”), the owner of the wind farm utility fleet, the Company supports the construction and maintenance of offshore wind turbines. In the past, the Company has operated supply and anchor handling towing supply vessels in this region. The Spin-off. SEACOR Marine was previously a subsidiary of SEACOR Holdings Inc. (along with its consolidated subsidiaries, other than SEACOR Marine, collectively referred to as “SEACOR Holdings”). On June 1, 2017, SEACOR Holdings completed a spin-off of SEACOR Marine by way of a pro rata dividend of SEACOR Marine’s Common Stock, all of which was then held by SEACOR Holdings, to SEACOR Holdings’ shareholders of record as of May 22, 2017 (the “Spin-off”). SEACOR Marine entered into certain agreements with SEACOR Holdings to 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. Immediately following the Spin-off, SEACOR Marine began to operate as an independent, publicly traded company. 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 employs the cost method of accounting for investments in 50% or less owned companies it does not control or exercise significant influence. These investments in private companies are carried at cost and are adjusted only for capital distributions and other-than-temporary declines in fair value. Use of Estimates. The preparation of financial statements in conformity with accounting principles generally accepted in the United States 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 doubtful accounts, 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 recognizes revenue when it is realized or realizable and earned. Revenue is realized or realizable and earned when persuasive evidence of an arrangement exists, delivery has occurred or services have been rendered, the price to the buyer is fixed or determinable, and collectability is reasonably assured. Revenue that does not meet these criteria is deferred until the criteria are met. Deferred revenues for the years ended December 31 were as follows (in thousands): 2017 2016 2015 Balance at beginning of year $ 6,953 $ 6,953 $ 6,794 Revenues deferred during the year 4,699 — 159 Revenues recognized during the year (1,548 ) — — Balance at end of year $ 10,104 $ 6,953 $ 6,953 As of December 31, 2017 , the Company deferred revenues of $6.8 million related to the time charter of several offshore support vessels scheduled to be paid through the conveyance of an overriding royalty interest (the “Conveyance”) in developmental oil and natural gas producing properties operated by a customer in the U.S. Gulf of Mexico. Payments under the Conveyance, and the timing of such payments, were contingent upon production and energy sale prices. On August 17, 2012, the customer filed a voluntary petition for Chapter 11 bankruptcy. The Company is vigorously defending its interest in connection with the bankruptcy filing; however, payments received under the Conveyance subsequent to May 19, 2012 are subject to creditors’ claims in bankruptcy court. The Company will recognize revenues when reasonably assured of a judgment in its favor. All costs and expenses related to these charters were recognized as incurred. As of December 31, 2017, the Company deferred revenues of $3.2 million related to the time charter of an offshore support vessel to a customer from which collection was not reasonably assured. The Company will recognize revenues when collected or when collection is reasonably assured. All costs and expenses related to this charter were recognized as incurred. The Company earns revenues primarily from the time charter and bareboat charter of vessels to customers based upon daily rates of hire. Therefore, 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 all risk 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 whereby 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. Contract or charter durations may range from several days to several years. Longer duration charters are more common where equipment is not as readily available or specific equipment is required. In the North Sea, multi-year charters have been more common and constitute a significant portion of that market. Time charters in Asia have historically been less common and generally contracts or charters have terms of less than two years. In the Company’s other operating areas, charters vary in length from short-term to multi-year periods, many with cancellation clauses and no early termination penalty. 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 actually 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 related to banking facility requirements. Marketable Securities. Marketable equity securities with readily determinable fair values and debt securities are reported in the accompanying consolidated balance sheets as marketable securities. These investments are stated at fair value, as determined by their market observable prices, with both realized and unrealized gains and losses reported in the accompanying consolidated statements of loss as marketable security losses, net. Short sales of marketable securities are stated at fair value in the accompanying consolidated balance sheets with both realized and unrealized losses reported in the accompanying consolidated statements of loss as marketable security gains (losses), net. Marketable securities are classified as trading securities for financial reporting purposes with gains and losses reported as operating activities in the accompanying consolidated statements of cash flows. Trade and Other Receivables. Customers are primarily major integrated national and international oil companies and large independent oil and natural gas exploration and production companies. Trade customers are granted credit on a short-term basis and related credit risks are considered minimal. Other receivables consist primarily of operating expenses incurred by the Company related to vessels it manages for others and insurance and income tax receivables. The Company routinely reviews its receivables and makes provisions for probable doubtful accounts; however, those provisions are estimates and actual results could differ from those estimates and those differences may be material. Trade receivables are deemed uncollectible and removed from accounts receivable and the allowance for doubtful accounts 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. There were no inventory write-downs during the years ended December 31, 2017 , 2016 , and 2015 . 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, 2017 , 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: Wind farm utility vessels 10 All other offshore support vessels (excluding wind farm utility) 20 The Company’s property and equipment as of December 31 was as follows (in thousands): Historical Cost (1) Accumulated Depreciation Net Book Value 2017 Offshore support vessels: Anchor handling towing supply $ 198,222 $ (174,159 ) $ 24,063 Fast support 424,865 (89,980 ) $ 334,885 Supply 105,360 (51,494 ) $ 53,866 Standby safety 118,414 (97,603 ) $ 20,811 Specialty 30,529 (19,304 ) $ 11,225 Liftboats 196,504 (54,161 ) $ 142,343 Wind farm utility 65,976 (40,358 ) $ 25,618 General machinery and spares 14,385 (13,244 ) $ 1,141 Other (2) 25,581 (19,857 ) $ 5,724 $ 1,179,836 $ (560,160 ) $ 619,676 2016 Offshore support vessels: Anchor handling towing supply $ 228,857 $ (183,757 ) $ 45,100 Fast support 251,415 (72,599 ) $ 178,816 Supply 96,774 (58,028 ) $ 38,746 Standby safety 109,436 (88,020 ) $ 21,416 Specialty 45,765 (24,063 ) $ 21,702 Liftboats 104,356 (45,447 ) $ 58,909 Wind farm utility 60,671 (29,019 ) $ 31,652 General machinery and spares 32,921 (20,008 ) $ 12,913 Other (2) 28,564 (19,678 ) $ 8,886 $ 958,759 $ (540,619 ) $ 418,140 _____________________ (1) Includes property and equipment acquired in business acquisitions at acquisition date fair value, and net of the impact of recognized impairment charges. (2) Includes land, buildings, leasehold improvements, vehicles and other property and equipment. Depreciation expense totaled $62.8 million , $58.0 million and $60.8 million in 2017 , 2016 and 2015 , 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 $3.6 million , $7.0 million and $4.4 million in 2017 , 2016 and 2015 , respectively. Intangible Assets. During the year ended December 31, 2016 , the Company wrote-off its intangible assets as part of recognized impairment charges associated with its liftboat fleet (see Impairment of Long-Lived Assets below). During the years ended 2016 and 2015 , the Company recognized amortization expense of $0.1 million and $0.9 million , 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 anchor handling towing supply 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, 2017, the Company recorded impairment charges of $27.5 million primarily associated with its anchor handling towing supply vessels, one leased-in supply vessel removed from service as it is not expected to be marketed prior to the expiration of its lease, one owned fast support vessel removed from service and two owned in-service specialty vessels. During the year ended December 31, 2016, the Company recorded impairment charges of $119.7 million primarily associated with its anchor handling towing supply fleet, its liftboat fleet and one specialty vessel. During the year ended December 31, 2015, the Company recorded impairment charges of $7.1 million primarily related to the suspended construction of two fast support vessels and the removal from service of one leased-in supply vessel. Estimated fair values for the Company’s owned vessels were established by independent appraisers and other market data such as recent sales of similar vessels (see Note 10). If market conditions further decline from the depressed utilization and rates per day worked experience over the last three years, fair values based on future appraisals could decline significantly. 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., fast support vessels), vessels required for customers to meet regulatory mandates and operating under multiple year contracts (e.g., standby safety vessels) or vessels that service customers outside of the offshore oil and natural gas market (e.g., wind farm utility vessels). For vessel classes and individual vessels with indicators of impairment but not recently impaired as of December 31, 2017, 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. During the years ended December 31, 2017 and 2016 , the Company recognized impairment charges of $8.8 million and $6.9 million , respectively, net of tax, related to its 50% or less owned companies (see Note 4). The Company did not recognize any impairment charges during the year ended December 31, 2015 . Goodwill . Goodwill is recorded when the purchase price paid for an acquisition exceeds the fair value of net identified tangible and intangible assets acquired. During the year ended December 31, 2015 , the Company recognized a $13.4 million impairment charge to fully impair all of its previously recorded goodwill. 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 2). 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 is 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. Prior to the Spin-off, SEACOR Marine was included in the consolidated U.S. federal income tax return of SEACOR Holdings. 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. Deferred Gains - Vessel Sale-Leaseback Transactions and Financed Vessel Sales . From time to time, the Company enters into vessel sale-leaseback transactions with finance companies or provides 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 is not immediately recognized in income and has been recorded in the accompanying consolidated balance sheets in deferred gains and other liabilities. In sale-leaseback transactions, gains are deferred to the extent of the present value of future minimum lease payments and are amortized as reductions to rental expense over the applicable lease terms. In financed vessel sales, gains are deferred to the extent that the repayment of purchase notes is dependent on the future operations of the sold vessels and are amortized based on cash received from the buyers. Deferred gain activity related to these transactions for the years ended December 31 was as follows (in thousands): 2017 2016 2015 Balance at beginning of year $ 32,035 $ 40,234 $ 50,934 Amortization of deferred gains included in operating expenses as reduction to rental expense (8,118 ) (8,199 ) (8,199 ) Amortization of deferred gains included in losses on asset dispositions and impairments, net — — (2,501 ) Other (364 ) — — Balance at end of year $ 23,553 $ 32,035 $ 40,234 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. Deferred gain activity related to these transactions for the years ended December 31 was as follows (in thousands): 2017 2016 2015 Balance at beginning

Business Acquisitions (Notes)

Business Acquisitions (Notes)	12 Months Ended
	Dec. 31, 2017
Business Combinations [Abstract]
Business Acquisitions	2. BUSINESS ACQUISITIONS Sea-Cat Crewzer. On April 28, 2017, the Company acquired a 100% controlling interest in Sea-Cat Crewzer, which owns an operates two high-speed offshore catamarans, through the acquisition of its partners’ 50% ownership interest for $4.4 million in cash (see Note 4). The Company performed a fair value analysis and the purchase price was allocated to the acquired assets and liabilities based on their fair values resulting in no goodwill being recorded. Sea-Cat Crewzer II. On April 28, 2017, the Company acquired a 100% controlling interest in Sea-Cat Crewzer II, which owns and operates two high-speed offshore catamarans, through the acquisition of its partners’ 50% ownership interest for $11.3 million in cash (see Note 4). The Company performed a fair value analysis and the purchase price was allocated to the acquired assets and liabilities based on their fair values resulting in no goodwill being recorded. Cypress CKOR. On December 12, 2016, the Company obtained a 100% controlling interest in Cypress CKOR LLC (“Cypress CKOR”), an owner of one offshore support vessel, for one dollar and the assumption of $3.1 million in debt. The Company performed a fair value analysis and the purchase price was allocated to the acquired assets and liabilities based on their fair values resulting in no goodwill being recorded. Purchase Price Allocation. The allocation of the purchase price for the Company’s acquisitions for the years ended December 31 was as follows (in thousands): 2017 2016 Restricted cash $ — $ 275 Trade and other receivables 235 1,250 Other current assets 4,148 — Investments, at Equity, and Advances to 50% or Less Owned Companies (15,700 ) — Property and Equipment 61,626 1,367 Accounts payable 747 199 Other current liabilities (76 ) — Long-Term Debt (41,186 ) (3,091 ) Other (43 ) — Purchase price (1) $ 9,751 $ — ______________________ (1) Purchase price in 2017 is net of cash acquired totaling $5.9 million . The impact of consolidating Falcon Global’s net assets effective March 31, 2017 to the Company’s financial position was as follows (in thousands): Cash $ 1,943 Marketable securities 785 Trade and other receivables (291 ) Investments, at Equity, and Advances to 50% or Less Owned Companies (19,374 ) Property and Equipment 96,000 Accounts payable 3,201 Other current liabilities 1,153 Long-Term Debt 58,335 Other Liabilities (1,000 ) Noncontrolling interests in subsidiaries 17,374

Investments, At Equity, And Adv

Investments, At Equity, And Advances To 50% Or Less Owned Companies	12 Months Ended
	Dec. 31, 2017
Equity Method Investment, Summarized Financial Information [Abstract]
Investments, At Equity, And Advances To 50% Or Less Owned Companies	4. INVESTMENTS, AT EQUITY, AND ADVANCES TO 50% OR LESS OWNED COMPANIES Investments, at equity, and advances to 50% or less owned companies as of December 31 were as follows (in thousands): Ownership 2017 2016 MexMar 49.0% $ 60,980 $ 63,404 OSV Partners 30.4% 10,006 9,245 Nautical Power 50.0% 6,408 6,413 Dynamic Offshore Drilling 19.0% 4,958 15,871 Falcon Global 50.0% — 18,539 Sea Cat Crewzer II 50.0% — 11,246 Sea-Cat Crewzer 50.0% — 4,088 Other 20.0% — 50.0% 9,817 9,505 $ 92,169 $ 138,311 Condensed Financial Information of MexMar. Summarized financial information of MexMar as of and for the years ended December 31 was as follows (in thousands): 2017 2016 Current assets $ 71,990 $ 50,996 Noncurrent assets 194,990 209,806 Current liabilities 23,931 23,089 Noncurrent liabilities 147,043 151,515 2017 2016 2015 Operating Revenues $ 67,003 $ 70,521 $ 78,363 Costs and Expenses: Operating and administrative 29,405 37,613 41,837 Depreciation 15,977 13,958 13,089 45,382 51,571 54,926 Operating Income $ 21,621 $ 18,950 $ 23,437 Net Income $ 9,233 $ 6,476 $ 15,638 Condensed Financial Information of Falcon Global, Sea-Cat Crewzer and Sea-Cat Crewzer II. Summarized financial information as of and for the years ended December 31 was as follows (in thousands): 2016 Current assets $ 14,834 Noncurrent assets 166,076 Current liabilities 9,624 Noncurrent liabilities 90,693 2017 (1) 2016 2015 Operating Revenues $ 5,075 $ 21,611 $ 24,439 Costs and Expenses: Operating and administrative 3,752 12,837 9,441 Depreciation 2,324 3,694 3,708 6,076 16,531 13,149 Operating Income (Loss) $ (1,001 ) $ 5,080 $ 11,290 Net Income (Loss) $ (2,699 ) $ 778 $ 6,468 _____________________ (1) Includes activity through date of acquisition or consolidation. Combined Condensed Financial Information of Other Investees (excluding MexMar, Falcon Global, Sea-Cat Crewzer and Sea-Cat Crewzer II). 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): 2017 2016 Current assets $ 61,360 $ 78,071 Noncurrent assets 247,038 255,270 Current liabilities 14,603 32,731 Noncurrent liabilities 138,789 158,628 2017 2016 2015 Operating Revenues $ 77,409 $ 77,571 $ 92,559 Costs and Expenses: Operating and administrative 46,748 51,136 57,922 Depreciation 12,198 13,181 13,961 58,946 64,317 71,883 Loss on Asset Dispositions and Impairments, Net — (21,323 ) (2,201 ) Operating Income $ 18,463 $ (8,069 ) $ 18,475 Net Income (Loss) $ 6,451 $ (19,229 ) $ 3,829 As of December 31, 2017 and 2016 , cumulative undistributed net earnings of 50% or less owned companies included in the Company’s consolidated retained earnings were $46.1 million and $38.7 million , respectively. MexMar. MexMar owns and operates 15 offshore support vessels in Mexico. During the year ended December 31, 2017 , MexMar returned advances of $7.4 million in cash to the Company. During the year ended December 31, 2016 , the Company made advances of $7.4 million in cash and sold two offshore support vessels for $34.0 million in cash to MexMar. During the year ended December 31, 2015 , the Company made advances of $7.9 million in cash to MexMar. In addition, during the year ended December 31, 2015 , MexMar repaid $15.0 million of seller financing provided by the Company. During the years ended December 31, 2017 , 2016 and 2015 , the Company received $0.3 million , $0.3 million and $0.4 million , respectively, of vessel management fees from MexMar. During the years ended December 31, 2016 and 2015 , the Company charged MexMar $5.1 million and $11.6 million , respectively, to charter certain vessels under bareboat and time charter arrangements. OSV Partners. SEACOR OSV Partners GP LLC and SEACOR OSV Partners I LP (collectively “OSV Partners”) own and operate five offshore support vessels. OSV Partners is currently in non-compliance with its debt service coverage ratio and its maximum leverage ratio pursuant to its term loan facility. As of December 31, 2017, the remaining principal amount outstanding under the facility was $29.3 million . During the year ended December 31, 2017 , the Company participated in a $6.0 million preferred equity offering of OSV Partners and invested $2.3 million in support of the venture. 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 fundings to OSV Partners. During the years ended December 31, 2016 and 2015 , the Company contributed capital of $1.2 million and $1.4 million , respectively, in cash to OSV Partners. During the year ended December 31, 2016 , equity in earnings (losses) of 50% or less owned companies, net of tax, includes $1.0 million related to the Company’s proportionate share of impairment charges associated with OSV Partners’ fleet. During the years ended December 31, 2017 , 2016 and 2015 , the Company received $0.6 million , $0.5 million and $1.2 million , respectively, of vessel management fees from OSV Partners. Nautical Power. As of December 31, 2017 , the Company’s investment in Nautical Power, LLC (“Nautical Power”) consists of its share of funds held for future investment. Dynamic Offshore Drilling. Dynamic Offshore Drilling Ltd. (“Dynamic Offshore Drilling”) was established to construct and operate a jack-up drilling rig that was delivered in the first quarter of 2013. During the year ended December 31, 2017 , the Company recognized an impairment charge of $8.3 million , net of tax, for an other than temporary decline in the fair value of its equity investment upon Dynamic Offshore Drilling’s unsuccessful bid on a charter renewal with a customer. Falcon Global. Falcon Global was formed to construct and operate two foreign-flag liftboats. During the three months ended March 31, 2017, the Company and its partner each contributed additional capital of $0.4 million , and the Company made working capital advances of $2.0 million to Falcon Global. In March 2017, the Company’s partner declined to participate in a capital call from Falcon Global and, as a consequence, the Company obtained 100% voting control of Falcon Global in accordance with the terms of the operating agreement. The impact of consolidating Falcon Global’s net assets effective March 31, 2017 to the Company’s financial position was as follows (in thousands): Cash $ 1,943 Marketable securities 785 Trade and other receivables (291 ) Investments, at Equity, and Advances to 50% or Less Owned Companies (19,374 ) Property and Equipment 96,000 Accounts payable 3,201 Other current liabilities 1,153 Long-Term Debt 58,335 Other Liabilities (1,000 ) Noncontrolling interests in subsidiaries 17,374 Sea-Cat Crewzer II. Sea-Cat Crewzer II owns and operates two high-speed offshore catamarans. On April 28, 2017, the Company acquired a 100% controlling interest in Sea-Cat Crewzer II through the acquisition of its partners’ 50% ownership interest for $11.3 million in cash (see Note 2). Sea-Cat Crewzer. Sea-Cat Crewzer owns and operates two high-speed offshore catamarans. On April 28, 2017, the Company acquired a 100% controlling interest in Sea-Cat Crewzer through the acquisition of its partners’ 50% ownership interest for $4.4 million in cash (see Note 2). Other. The Company’s other 50% or less owned companies own and operate nine vessels. During the year ended December 31, 2017 , the Company received dividends of $2.6 million , made capital contributions and advances of $0.8 million and received repayments on advances of $0.2 million with these 50% or less owned companies. In addition, during the year ended December 31, 2017 , the Company recognized impairment charges of $0.5 million , net of tax, for an other-than-temporary decline in the fair value of its investment in a certain 50% or less owned company. During the year ended December 31, 2016 , the Company received dividends of $0.8 million from these 50% or less owned companies and made capital contributions of $0.5 million to these 50% or less owned companies. In addition, during the year ended December 31, 2016 , the Company recognized impairment charges of $0.5 million , net of tax, for an other-than-temporary decline in the fair value of its investment in a certain 50% or less owned company and recognized $2.7 million , net of tax, for its proportionate share of impairment charges recognized by certain of its 50% or less owned companies related to offshore support vessels used in their operations. During the year ended December 31, 2015, the Company received dividends of $0.9 million and repayments on advances of $0.2 million from these 50% or less owned companies. In addition, during the year ended December 31, 2015 , the Company recognized impairment charges of $2.0 million , net of tax, for its proportionate share of impairment charges recognized by certain of its 50% or less owned companies related to offshore support vessels used in their operations. During the years ended December 31, 2017 , 2016 and 2015 , the Company received $0.7 million , $0.8 million and $0.8 million , respectively, of vessel management fees from these 50% or less owned companies. Two of the Company’s 50% or less owned companies obtained bank debt to finance the acquisition of offshore support vessels. The debt is secured by, among other things, a first preferred mortgage on the vessels. The banks also have the authority to require the Company and its partners to fund uncalled capital commitments, as defined in the partnership agreements. In such event, the Company would be required to contribute its allocable share of uncalled capital, which was $1.4 million in the aggregate as of December 31, 2017. The Company guarantees certain of the outstanding charter receivables of one of its managed 50% or less owned companies if a customer defaults in payment and the Company either fails to take enforcement action against the defaulting customer or fails to assign its right of recovery against the defaulting customer. As of December 31, 2017, the Company’s contingent guarantee for the outstanding charter receivables was $0.4 million . SEACOSCO. On January 17, 2018, the Company announced the formation of SEACOSCO Offshore LLC (“SEACOSCO”), a Marshall Islands entity jointly owned by the Company and affiliates of COSCO SHIPPING GROUP (“COSCO SHIPPING”), the world’s largest ship owner. SEACOSCO entered into contracts for the purchase of eight Rolls-Royce designed, new construction platform supply vessels (“PSVs”) from COSCO SHIPPING HEAVY INDUSTRY (GUANGDONG) CO., LTD (the “Shipyard”, an affiliate of COSCO SHIPPING) for approximately $161.1 million , of which 70% will be financed by the Shipyard, and secured by the PSVs on a non-recourse basis to the Company. SEACOSCO will take title to seven of the PSVs in 2018 and one in 2019. Thereafter, the Shipyard, at its cost, will store the PSVs at its facility for periods ranging from six to 18 months. The Company’s total committed investment for construction and working capital requirements is approximately $27.5 million for an unconsolidated 50% interest in SEACOSCO, with approximately $20.0 million payable in the first quarter of 2018 and the remaining balance due over the next 14 months as the vessels and the equipment are delivered. The Company will be responsible for full commercial, operational, and technical management of the vessels on a worldwide basis.

Construction Reserve Funds Cons

Construction Reserve Funds Construction Reserve Funds (Notes)	12 Months Ended
	Dec. 31, 2017
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Construction Reserve Funds Disclosure [Text Block]	5. CONSTRUCTION RESERVE FUNDS 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. 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 the Maritime Administration. 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 extensions that can be granted at the discretion of the Maritime Administration, or be released for the Company’s general use as nonqualified withdrawals. For nonqualified withdrawals, the Company is obligated to pay taxes on the previously deferred gains at the prevailing statutory tax rate plus penalties and interest thereon for the period such taxes were deferred. As of December 31, 2017 and 2016, the Company’s construction reserve funds are classified as non-current assets in the accompanying consolidated balance sheets as the Company has the intent and ability to use the funds to acquire equipment. Construction reserve fund transactions for the years ended December 31 were as follows (in thousands): 2017 2016 2015 Withdrawals $ (39,163 ) $ (87,820 ) $ (24,871 ) Deposits 6,315 27,414 18,054 $ (32,848 ) $ (60,406 ) $ (6,817 )
Schedule of Construction Reserve Funds [Table Text Block]	Construction reserve fund transactions for the years ended December 31 were as follows (in thousands): 2017 2016 2015 Withdrawals $ (39,163 ) $ (87,820 ) $ (24,871 ) Deposits 6,315 27,414 18,054 $ (32,848 ) $ (60,406 ) $ (6,817 )

Third Party Notes Receivable

Third Party Notes Receivable	12 Months Ended
	Dec. 31, 2017
Notes, Loans and Financing Receivable, Net, Noncurrent [Abstract]
Loans, Notes, Trade and Other Receivables Disclosure [Text Block]	6. LEASES AND NOTES RECEIVABLE FROM THIRD PARTIES From time to time, the Company engages in lending activities involving various types of equipment. The Company recognizes interest income as payments are due, typically monthly, and expenses all costs associated with its lending activities as incurred. These notes receivable are typically collateralized by the underlying equipment and require periodic principal and interest payments. During the year ended December 31, 2015, the Company purchased a third party note receivable from SEACOR Holdings secured by offshore marine equipment for $13.6 million (see Note 18). During the year ended December 31, 2016 , the Company recognized reserves of $1.8 million for this note receivable following non-performance and a decline in the underlying collateral values and exchanged the note receivable for the underlying collateral (see Note 10), which is included in property and equipment in the accompanying consolidated balance sheets.

Long-Term Debt

Long-Term Debt	12 Months Ended
	Dec. 31, 2017
Long-term Debt, Unclassified [Abstract]
Long-Term Debt	7. LONG-TERM DEBT The Company’s long-term debt obligations as of December 31 were as follows (in thousands): 2017 2016 3.75% Convertible Senior Notes $ 175,000 $ 175,000 Falcon Global Term Loan Facility 54,870 — Sea-Cat Crewzer III Term Loan Facility 29,078 22,785 Windcat Workboats Facilities 25,202 22,118 Sea-Cat Crewzer II Term Loan Facility 20,871 — Sea-Cat Crewzer Term Loan Facility 18,504 — C-Lift Acquisition Notes 16,000 17,500 BNDES Equipment Construction Finance Notes 7,234 9,186 Cypress CKOR Term Loan 1,300 2,452 348,059 249,041 Portion due within one year (22,858 ) (20,400 ) Debt discount (27,373 ) (4,567 ) Issue costs (5,787 ) (6,269 ) $ 292,041 $ 217,805 The Company’s contractual long-term debt maturities for the years ended December 31 were as follows (in thousands): 2018 $ 22,858 2019 54,533 2020 10,358 2021 34,989 2022 208,618 Years subsequent to 2022 16,703 $ 348,059 3.75% Convertible Senior Notes. On December 1, 2015, the Company issued $175.0 million aggregate principal amount of its 3.75% Convertible Senior Notes due December 1, 2022 (the “ 3.75% Convertible Senior Notes”) to investment funds managed and controlled by the Carlyle Group. Interest on the 3.75% Convertible Senior Notes is payable semi-annually on June 15 and December 15 of each year, commencing June 15, 2016. Upon consummation of a fundamental change in the Company, as more fully described in the indenture, the Company may redeem all the 3.75% Convertible Senior Notes for cash at a price equal to the greater of 100% of the principal amount, plus accrued and unpaid interest to the date of redemption, or the fair value of consideration the holders of the 3.75% Convertible Senior Notes would have received if exchanged or converted into the Company immediately prior to the fundamental change (the “Fundamental Change Call”). The 3.75% Convertible Senior Notes are convertible into shares of SEACOR Marine Holdings common stock, par value $0.01 per share (“Common Stock”), at a conversion rate of 23.26 shares per $1,000 principal amount of the notes only if certain conditions are met, as more fully described in the indenture. The Company, at its option, may under certain circumstances settle any of the 3.75% Convertible Senior Notes submitted for conversion into its Common Stock through the issuance of an equal number of warrants in order to facilitate the Company’s compliance with the provisions of the Jones Act. The warrants, if issued, would entitle their holders to purchase an equal number of shares of Common Stock at an exercise price of $0.01 per share upon the resolution of any Jones Act compliance issues. The Company has reserved the maximum number of shares of Common Stock needed upon conversion of the notes and potential exercise of warrants, or 4,070,500 shares, as of December 31, 2017 . If the Company undergoes a fundamental change, the holders of the 3.75% Convertible Senior Notes may require the Company to purchase for cash all or part of the Notes at a price equal to 100% of the principal amount, plus accrued and unpaid interest to the date of purchase. The 3.75% Convertible Senior Notes may be redeemed, in whole or in part, only if certain conditions are met, as more fully described in the indenture, at a price equal to 100% of the principal amount, plus accrued and unpaid interest to the date of redemption. On November 30, 2015, SEACOR Holdings and the holders of the 3.75% Convertible Senior Notes also entered into an exchange agreement whereby the holders could have elected to exchange the principal amount of their outstanding notes, in whole or in part, into shares of SEACOR Holdings’ common stock (the “Exchange Option”). The fair value of the financial support received by the Company upon SEACOR Holdings’ issuance of the Exchange Option was recorded as an equity contribution from SEACOR Holdings with a corresponding debt discount to the 3.75% Convertible Senior Notes. The Company had no obligations to SEACOR Holdings or the holders of the 3.75% Convertible Senior Notes under the Exchange Option. The debt discount of $8.5 million and issue costs of $6.4 million was being amortized as additional non-cash interest expense over the two year period for which the debt was expected to be outstanding for an overall effective interest rate of 8.7% . Upon completion of the Spin-off, the Exchange Option terminated. Upon completion of the Spin-off, the Company bifurcated the embedded conversion option liability of $27.3 million from the 3.75% Convertible Senior Notes and recorded an additional debt discount (see Notes 9 and 10). 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 is recorded as derivative income or loss. Falcon Global Term Loan Facility. On August 3, 2015, Falcon Global entered into a term loan facility to finance the construction of two foreign-flag liftboats. The facility consisted of two tranches: (i) a $62.5 million facility to fund the construction costs of the liftboats (“Tranche A”) and (ii) a $18.0 million facility for certain project costs (“Tranche B”). Borrowings under the facility bear interest at variable rates based on LIBOR plus a margin, currently 5.25% as of December 31, 2017 . The facility is secured by the liftboats and is repayable over a five year period that began after the completion of the construction of the liftboats and matures June 30, 2022. On November 3, 2017, Falcon Global executed an amendment to its term loan facility, at a cost of $0.2 million , that requires Falcon Global to maintain a debt service coverage ratio and a minimum cash balance on hand in excess of defined thresholds. In addition, the amendment requires SEACOR Marine, as guarantor, to maintain a debt to capital ratio below a defined threshold and a minimum cash balance on hand in excess of a defined threshold. In March 2017, the Company’s partner declined to participate in a capital call from Falcon Global and, as a consequence, the Company obtained 100% voting control of Falcon Global in accordance with the terms of the operating agreement. The Company consolidated into its financial statements Falcon Global’s then outstanding debt under this facility of $58.3 million , net of issue costs of $1.0 million , effective March 31, 2017 (see Note 4). During April 2017, the Tranche B facility was canceled prior to any funding. During the nine months ended December 31, 2017 , Falcon Global made scheduled payments of $4.4 million under Tranche A. 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 US dollars) secured by the Company’s vessels and fully guaranteed by SEACOR Marine. 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 year ended December 31, 2017 , Sea-Cat Crewzer III made scheduled payments of $0.6 million related to this facility. Windcat Workboats Facilities. On May 24, 2016 , Windcat Workboats entered into a €25.0 million revolving credit facility secured by the Company’s wind farm utility vessel fleet. Borrowings under the facility bear interest at variable rates based on EURIBOR plus a margin ranging from 3.00% to 3.30% per annum plus mandatory lender costs and mature in 2021. A quarterly commitment fee is payable based on the unfunded portion of the commitment amount at rates ranging from 1.20% to 1.32% per annum. During the year ended December 31, 2016 , Windcat Workboats drew $23.5 million ( €21.0 million ) under the facility to repay all of its then outstanding debt totaling $22.9 million and incurred issuance costs of $0.6 million related to this facility. Prior to May 24, 2016, Windcat Workboats had euro denominated acquisition notes and euro and pound sterling denominated equipment notes secured by the Company’s wind farm utility vessel fleet. During the year ended December 31, 2015, the Company made scheduled payments of $3.2 million . Sea-Cat Crewzer II Term Loan Facility. On April 28, 2017 , the Company acquired a 100% controlling interest in Sea-Cat Crewzer II through the acquisition of its partners’ 50% ownership interest (see Notes 2 and 4). Sea-Cat Crewzer II has a term loan facility that matures in 2019 which is secured by a first preferred mortgage on its vessels. On December 19, 2017, Sea-Cat Crewzer II executed an amendment, at a cost of $0.1 million , that replaced SEACOR Holdings with SEACOR Marine as guarantor and requires SEACOR Marine to maintain a debt to capital ratio below a defined threshold and a minimum cash balance on hand in excess of a defined threshold. The facility calls for quarterly payments of principal and interest with a balloon payment of $17.3 million due at maturity. The interest rate is fixed at 1.52% , inclusive of an interest rate swap, plus a margin ranging from 2.10% to 2.75% subject to the level of funded debt (overall rate of 5.64% as of December 31, 2017 ). Since April 28, 2017, the Company made scheduled payments of $1.2 million . Sea-Cat Crewzer Term Loan Facility. On April 28, 2017 , the Company acquired a 100% controlling interest in Sea-Cat Crewzer through the acquisition of its partners’ 50% ownership interest (see Notes 2 and 4). Sea-Cat Crewzer has a term loan facility that matures in 2019 which is secured by a first preferred mortgage on its vessels. On December 19, 2017, Sea-Cat Crewzer executed an amendment, at a cost of $0.1 million , that replaced SEACOR Holdings with SEACOR Marine as guarantor and requires SEACOR Marine to maintain a debt to capital ratio below a defined threshold and a minimum cash balance on hand in excess of a defined threshold. The facility calls for quarterly payments of principal and interest with a balloon payment of $15.3 million due at maturity. The interest rate is fixed at 1.52% , inclusive of an interest rate swap, plus a margin ranging from 2.10% to 2.75% subject to the level of funded debt (overall rate of 5.64% as of December 31, 2017 ). Since April 28, 2017, the Company made scheduled payments of $1.1 million . C-Lift Acquisition Notes. The Company assumed these notes following the purchase of its partner’s 50% interest in C-Lift. The notes are secured by a first mortgage on two liftboats. On December 13, 2017, C-Lift executed an amendment, at a cost of $0.1 million , that replaced SEACOR Holdings with SEACOR Marine as guarantor and requires SEACOR Marine to maintain a debt to capital ratio below a defined threshold and a minimum cash balance on hand in excess of a defined threshold. The notes bear interest at variable rates based on LIBOR plus a fixed margin and resets quarterly ( 6.19% as of December 31, 2017 ). The notes mature in December 2019. During the years ended December 31, 2017 , 2016 and 2015 , the Company made scheduled payments of $1.5 million , $1.7 million , and $1.6 million , respectively. BNDES Equipment Construction Finance Notes. The Company financed the construction of certain offshore support vessels in Brazil with Banco Nacional de Desenvolvimento Economico e Social (“BNDES”), a Brazilian government-owned entity. The notes are secured by a first mortgage on these vessels and guaranteed by SEACOR Holdings. The notes bear interest at 4.00% per annum, require monthly principal and interest payments, and mature in July through October 2021. During the years ended December 31, 2017 , 2016 and 2015 , the Company made scheduled payments of $2.0 million , $2.0 million and $2.0 million , respectively. Cypress CKOR Term Loan. On December 12, 2016 , the Company obtained a 100% controlling interest in Cypress CKOR, an owner of one offshore support vessel, for one dollar and the assumption of $3.1 million in debt (see Note 2). During the years ended December 31, 2017 and 2016 , the Company made scheduled payments of $1.2 million and $0.6 million , respectively. Letters of Credit. As of December 31, 2017 , the Company had outstanding letters of credit totaling $2.8 million for labor and performance guarantees.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Income Taxes	8. INCOME TAXES 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): 2017 2016 2015 United States $ (90,696 ) $ (169,523 ) $ (47,184 ) Foreign (45,112 ) (28,095 ) (1,963 ) Eliminations 18,785 7,313 (3,429 ) $ (117,023 ) $ (190,305 ) $ (52,576 ) As of December 31, 2017, cumulative undistributed net earnings of foreign subsidiaries included in the Company’s retained earnings were $38.5 million . The components of income tax benefit for the years ended December 31 were as follows (in thousands): 2017 2016 2015 Current: Federal $ (16,705 ) $ (20,718 ) $ (6,814 ) State (42 ) (139 ) 420 Foreign 3,347 5,436 5,907 (13,400 ) (15,421 ) (487 ) Deferred: Federal (60,750 ) (47,692 ) (15,956 ) State (172 ) (446 ) (14 ) Foreign (84 ) 90 (516 ) (61,006 ) (48,048 ) (16,486 ) $ (74,406 ) $ (63,469 ) $ (16,973 ) 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: 2017 2016 2015 Statutory rate (35.0 )% (35.0 )% (35.0 )% U.S. federal income tax law changes (37.3 )% — % — % SEACOR Holdings share awards to Company personnel 2.3 % 0.4 % 0.1 % Non-deductible expenses 1.8 % 0.1 % 1.8 % Exclusion of foreign subsidiaries with accumulated losses 2.7 % 1.1 % 0.5 % Noncontrolling interests 1.7 % 0.2 % (0.5 )% State taxes (0.2 )% (0.3 )% 0.5 % Other 0.4 % 0.1 % 0.3 % (63.6 )% (33.4 )% (32.3 )% For the year ending December 31, 2017, the Company’s effective income tax rate of 63.6% was higher than the Company’s statutory tax rate of 35% primarily due to income tax benefits of $43.7 million recognized as a result of new U.S. tax legislation signed into law on December 22, 2017. The majority of the income tax benefits recognized were due to a reduction in U.S. tax rates from 35% to 21% applied to the Company’s domestic basis differences and the elimination of previously accrued deferred taxes on the unremitted earnings of the Company’s foreign subsidiaries. The components of net deferred income tax liabilities as of December 31 were as follows (in thousands): 2017 2016 Deferred tax liabilities: Property and equipment $ 55,262 $ 98,654 Unremitted earnings of foreign subsidiaries — 24,084 Investments in 50% or Less Owned Companies 4,258 15,203 Other 5,901 2,260 Total deferred tax liabilities 65,421 140,201 Deferred tax assets: Federal Net Operating Loss Carryforwards 5,111 — Other 5,373 15,256 10,484 15,256 Valuation Allowance (569 ) — Total deferred tax assets 9,915 15,256 Net deferred tax liabilities $ 55,506 $ 124,945 As of December 31, 2017, the Company’s valuation allowance of $0.6 million related to various state net operating loss carryforwards. The estimated impact of the new U.S. tax legislation signed into law on December 22, 2017 is based on management’s current knowledge and assumptions. As of December 31, 2017, the Company’s federal net operating loss carryforwards excluded unrecognized tax benefits of $3.9 million as a result of uncertainty regarding the interpretation of the new tax law. The recognition of these unrecognized tax benefits, as well as any other items identified upon the Company’s further analysis of the new tax law, will affect the Company’s effective tax rate in future periods, which could be materially different from the current estimates recorded.

Derivative Instruments And Hedg

Derivative Instruments And Hedging Strategies	12 Months Ended
	Dec. 31, 2017
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative Instruments And Hedging Strategies	9. 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 as of December 31 were as follows (in thousands): 2017 2016 Derivative (1) Derivative (2) Derivative (1) Derivative (2) Derivatives designated as hedging instruments: Forward currency exchange contracts (fair value hedges) $ — $ — $ — $ 316 Interest rate swap agreements (cash flow hedges) 260 20 — 73 260 20 — 389 Derivatives not designated as hedging instruments: Conversion option liability on 3.75% Convertible Senior Notes — 6,832 — — Forward currency exchange, option and future contracts — — 195 158 Interest rate swap agreements 159 46 — — $ 419 $ 6,898 $ 195 $ 547 _________________ (1) Included in other receivables in the accompanying consolidated balance sheets. (2) Included in other current liabilities in the accompanying consolidated balance sheets, except for the conversion option liability on the 3.75% Convertible Senior Notes. Fair Value Hedges. From time to time, the Company may designate certain of its foreign currency exchange contracts as fair value hedges in respect of capital commitments denominated in foreign currencies. By entering into these foreign currency exchange contracts, the Company may fix a portion of its capital commitments denominated in foreign currencies in U.S. dollars to protect against currency fluctuations. During the years ended December 31, 2017 and 2016, the Company recognized gains of $0.1 million and losses of $0.8 million , respectively, on these contracts which were recognized to the corresponding hedged equipment included in construction in progress in the accompanying condensed 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. 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 gains on derivative instruments designated as cash flow hedges of $0.2 million for the year ended December 31, 2017 and losses of $2.5 million and $1.2 million for the years ended December 31, 2016 , and 2015 , respectively, as a component of other comprehensive loss. As of December 31, 2017 , 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)% on the aggregate notional value of €15.0 million ( $18.0 million ) and receive a variable interest rate based on EURIBOR on the aggregate notional value. • Sea-Cat Crewzer II had an interest rate swap agreement maturing in 2019 that calls for Sea-Cat Crewzer II to pay a fixed rate of interest of 1.52% on the amortized notional value of $20.9 million and receive a variable interest rate based on LIBOR on the amortized notional value. • Sea-Cat Crewzer had an interest rate swap agreement maturing in 2019 that calls for Sea-Cat Crewzer to pay a fixed rate of interest of 1.52% on the amortized notional value of $18.5 million and receive a variable interest rate based on LIBOR on the amortized notional value. • MexMar 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% on the aggregate amortized notional value of $110.8 million and receive a variable interest rate based on LIBOR on the aggregate amortized notional value. 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 2017 2016 2015 Conversion option liability on 3.75% Convertible Senior Notes $ 20,422 $ — $ — Interest rate swap agreements 46 (18 ) (18 ) Options on equities — 3,095 (2,748 ) Forward currency exchange, option and future contracts (212 ) (82 ) — $ 20,256 $ 2,995 $ (2,766 ) The conversion option liability relates to the bifurcated embedded conversion option in the 3.75% Convertible Senior Notes (See Notes 7 and 10). The Company and certain of the Company’s 50% or less owned companies have entered into interest rate swap agreements for the general purpose of providing protection against increases in interest rates, which might lead to higher interest costs. As of December 31, 2017, the interest rate swaps held by the Company or its 50% or less owned companies were as follows: • Falcon Global had an interest rate swap agreement maturing in 2022 that calls for Falcon Global to pay a fixed rate of interest of 2.06% on the amortized notional value of $56.3 million and receive a variable interest rate based on LIBOR on the amortized notional value. • OSV Partners had two interest rate swap agreements with maturities in 2020 that call for OSV Partners to pay a fixed rate of interest ranging from 1.89% to 2.27% on the aggregate amortized notional value of $33.0 million and receive a variable interest rate based on LIBOR on the aggregate amortized notional value. • Dynamic Offshore Drilling had an interest rate swap agreement maturing in 2018 that calls for Dynamic Offshore Drilling to pay a fixed interest rate of 1.30% on the amortized notional value of $64.2 million and receive a variable interest rate based on LIBOR on the amortized notional value. Prior to 2017, the Company held positions in publicly traded equity options that convey the right or obligation to engage in a future transaction on the underlying equity security or index. The Company’s investment in equity options primarily included positions in energy related businesses. These contracts were typically entered into to mitigate the risk of changes in market value of marketable security positions that the Company was either about to acquire, had acquired or was about to dispose. 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 United States. The Company generally does not enter into contracts with forward settlement dates beyond twelve to eighteen months. There are no outstanding contracts at December 31, 2017 .

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Fair Value Measurements	10. FAIR VALUE MEASUREMENTS 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 inputs are quoted prices in active markets for identical assets or liabilities. Level 2 inputs are observable inputs other than quoted prices included in Level 1 that are observable for the asset or liability, either directly or indirectly, including quoted prices for similar assets or liabilities in active markets, quoted prices in markets that are not active, inputs other than quoted prices that are observable for the asset or liability, or inputs derived from observable market data. Level 3 inputs are unobservable inputs that are supported by little or no market activity and are significant to the fair value of the assets or liabilities. 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 2017 ASSETS Derivative instruments (included in other receivables) $ — $ 419 $ — Construction reserve funds 45,361 — — LIABILITIES Derivative instruments (included in other current liabilities) — 66 — Conversion Option Liability on 3.75% Convertible Senior Notes — — 6,832 2016 ASSETS Marketable securities $ 40,139 $ — $ — Derivative instruments (included in other receivables) — 195 — Construction reserve funds 78,209 — — LIABILITIES Derivative instruments (included in other current liabilities) — 547 — Level 3 Measurement. The fair value of the conversion option liability on the 3.75% 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 exchanging 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): Carrying Amount Estimated Fair Value Level 1 Level 2 Level 3 2017 ASSETS Cash, cash equivalents and restricted cash $ 112,551 $ 112,551 $ — $ — Investments, at cost, in 50% or less owned companies (included in other assets) 132 see below LIABILITIES Long-term debt, including current portion 314,899 — 291,932 — 2016 ASSETS Cash, cash equivalents and restricted cash $ 118,771 $ 118,771 $ — $ — Investments, at cost, in 50% or less owned companies (included in other assets) 132 see below LIABILITIES Long-term debt, including current portion 238,205 — 242,404 — 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 2017 ASSETS Property and equipment: Anchor handling towing supply $ — $ 12,400 $ — Fast support — 175 — Specialty — 750 — Investments, at equity, in 50% or less owned companies — 20,658 20,430 2016 ASSETS Property and equipment: Anchor handling towing supply $ — $ 2,600 $ 42,500 Fast support — 50 — Supply — 2,153 1,800 Specialty — 4,000 — Liftboats — — 62,830 Investments, at equity, in 50% or less owned companies — — 18,539 Notes receivable from third parties (included in other assets) — — 11,900 Property and equipment. During the years ended December 31, 2017 and 2016, the Company recognized impairment charges of $27.5 million and $119.7 million , respectively, associated with certain offshore support vessels (see Note 1). 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. The significant unobservable inputs used in the fair value measurement for the anchor handling towing supply fleet during 2016 were the estimated construction costs for similar new equipment of $364.0 million , estimated economic fleet depreciation of 55% based on average expected remaining useful life and estimated economic obsolescence of 74% . The significant unobservable inputs used in the fair value measurement for the liftboat fleet during 2016 were the estimated construction costs for similar new equipment of $279.0 million , estimated economic fleet depreciation of 42% based on average expected remaining useful life and estimated average economic obsolescence of 61% . Investments, at equity, in 50% or less owned companies. During the years ended December 31, 2017 and 2016, the Company marked its investments to fair value in certain of its 50% or less owned companies. The Level 2 fair values were determined based on the purchase price of acquired interests or sales prices of similar equipment held in the venture. The Level 3 fair values were determined based on third-party valuations using significant inputs that are unobservable in the market. The significant Level 3 valuations were as follows: • The Company’s partner declined to participate in a capital call from Falcon Global during 2017 and, as a consequence, the Company obtained 100% voting control of Falcon Global in accordance with the terms of the operating agreement (see Note 4). Upon the change in control, the Company’s investment in Falcon Global was deemed to approximate fair value as a result of its recent impairment (see below). • The Company identified indicators of impairment in its investment in Falcon Global during 2016 as a result of continuing weak market conditions and, as a consequence, recognized a $6.4 million impairment charge, net of tax, for an other-than-temporary decline in fair value. Falcon Global’s primary assets consist of two liftboats in the final stages of construction and the estimated fair value of the liftboats was the primary input used by the Company in determining the fair value of its investment (see Note 4) and resulting impairment charge. The fair value of the liftboats was determined based on a third-party valuation using significant inputs that are unobservable in the market and therefore are considered a Level 3 fair value measurement. Due to limited market transactions, the primary valuation methodology applied by the appraisers was an estimated cost approach less economic obsolescence based on utilization and rates per day worked trending over the prior year in the Middle East region where the vessels are intended to operate. The significant unobservable inputs used in the fair value measurement were the estimated construction costs of similar new equipment and economic obsolescence of 25% . Notes receivable from third parties. During the year ended December 31, 2016, the Company recorded a $1.8 million reserve for its note receivable from a third party following non-performance and a decline in the underlying collateral value. The reserve was based on a third-party valuation of the underlying collateral using significant inputs that are unobservable in the market and therefore are considered a Level 3 fair value measurement. 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 assets and less estimated economic obsolescence. The significant unobservable inputs used in the fair value measurement were the estimated construction costs of similar new equipment and estimated economic depreciation of 33% and estimated obsolescence of 56% (see Note 6).

Common Stock Common Stock (Note

Common Stock Common Stock (Notes)	12 Months Ended
	Dec. 31, 2017
Treasury Stock Transactions, Excluding Value of Shares Reissued [Abstract]
Common Stock Disclosure [Text Block]	11. STOCKHOLDERS’ EQUITY On January 1, 2015, SEACOR Holdings contributed all of its majority-owned subsidiaries that provide offshore marine services to SEACOR Marine, except for an immaterial energy logistics business that was liquidated in December 2015. Any subsidiaries not providing offshore marine services and previously owned by the contributed subsidiaries were distributed to, or purchased by, SEACOR Holdings prior to the contribution. The Company received $6.9 million from SEACOR Holdings relating to the purchase of certain of these subsidiaries at carrying value, which was recorded as a capital contribution at the formation of SEACOR Marine. On December 1, 2015, SEACOR Holdings issued the Exchange Option in support of the Company’s issuance of its 3.75% Convertible Senior Notes. The fair value of the financial support received by the Company was $5.5 million , net of tax, and was recorded as an equity contribution from SEACOR Holdings. The Company had no obligations to SEACOR Holdings or the holders of the 3.75% Convertible Senior Notes in respect of the Exchange Option (see Note 7). The Company paid cash dividends of $1.8 million to SEACOR Holdings during the year ended December 31, 2015 .

Noncontrolling Interests in Sub

Noncontrolling Interests in Subsidiaries (Notes)	12 Months Ended
	Dec. 31, 2017
Noncontrolling Interest [Abstract]
Noncontrolling Interest Disclosure [Text Block]	12. NONCONTROLLING INTERESTS IN SUBSIDIARIES Noncontrolling interests in the Company’s consolidated subsidiaries as of December 31 were as follows (in thousands): Noncontrolling Interests 2017 2016 Falcon Global 50.0% $ 12,087 $ — Windcat Workboats 12.5% 2,608 5,266 Other 1.8 % — 30% 280 278 $ 14,975 $ 5,544 Falcon Global. Falcon Global was formed to construct and operate two foreign-flag liftboats. In March 2017, the Company’s partner declined to participate in a capital call from Falcon Global and, as a consequence, the Company obtained 100% voting control of Falcon Global in accordance with the terms of the operating agreement and began consolidating Falcon Global’s net assets effective March 31, 2017 (see Note 4). As of December 31, 2017, the net assets of Falcon Global were $24.2 million . During the nine months ended December 31, 2017 (the period which Falcon Global has been consolidated into the Company’s financial statements), the net loss of Falcon Global was $10.6 million , of which $5.3 million was attributable to noncontrolling interests. On February 9, 2018, the Company announced that the formation and capitalization of a joint venture between a wholly owned subsidiary of the Company and Montco Offshore, LLC (“MOI”, an affiliate of our partner in Falcon Global) was consummated on February 8, 2018. In connection therewith and MOI’s plan of reorganization, which was confirmed on January 18, 2018, MOI emerged from its Chapter 11 bankruptcy case. In accordance with the terms of a Joint Venture Contribution and Formation Agreement, the Company and MOI contributed certain liftboat vessels and other related assets, including each partner’s 50% interest in Falcon Global, to Falcon Global Holdings LLC (“FGH”) and its designated subsidiaries, and FGH and its designated subsidiaries assumed certain operating liabilities and indebtedness associated with the liftboat vessels and related assets. On February 8, 2018, Falcon Global USA LLC (“FGUSA”), a wholly owned subsidiary of FGH, paid $15.0 million of MOI’s debtor-in-possession obligations and entered into a $131.1 million credit agreement comprised of a $116.1 million term loan and a $15.0 million revolving loan facility (the “FGUSA Credit Facility”). The full amount of the term loan and other amounts paid by affiliates of MOI satisfied in full the amounts outstanding under MOI’s pre-petition credit facilities. The FGUSA Credit Facility, apart from a guarantee of certain interest payments and participation fees for two years after the closing of the transactions, is non-recourse to SEACOR Marine and its subsidiaries other than FGUSA. The Company will consolidate FGH as the Company holds approximately 72% of the equity interest in FGH and is entitled to appoint a majority of the board of managers of FGH. Immediately following the capitalization of FGH, the Company borrowed $5.0 million under the revolving loan facility for working capital purposes. Windcat Workboats. Windcat Workboats owns and operates the Company’s wind farm utility vessels that are primarily used to move personnel and supplies in the major offshore wind markets of Europe. During the year ended December 31, 2017, the Company acquired an additional 12.5% of Windcat Workboats from noncontrolling interests for $3.7 million . As of December 31, 2017 and 2016 , the net assets of Windcat Workboats were $20.8 million and $21.1 million , respectively. During the year ended December 31, 2017 , the net loss of Windcat Workboats was $2.1 million , of which $0.4 million was attributable to noncontrolling interests. During the year ended December 31, 2016 , the net loss of Windcat Workboats was $4.5 million , of which $1.1 million was attributable to noncontrolling interests. During the year ended December 31, 2015 , the net income of Windcat Workboats was $1.6 million , of which $0.4 million was attributable to noncontrolling interests.

Savings Plans And Multiemployer

Savings Plans And Multiemployer Pension Plans	12 Months Ended
	Dec. 31, 2017
Deferred Compensation Arrangements [Abstract]
Savings Plans And Multiemployer Pension Plans	13. SAVINGS AND MULTI-EMPLOYER PENSION PLANS SEACOR Marine Savings Plan. On January 1, 2016, the Company’s eligible U.S. based employees were transferred to the “SEACOR Marine 401(k) Plan,” a new Company sponsored defined contribution plan. The Company currently does not contribute to the SEACOR Marine 401(k) Plan. The SEACOR Marine 401(k) Plan costs for the year ended December 31, 2017 and 2016 were not material. Prior to January 1, 2016, the Company participated in a SEACOR Holdings sponsored defined contribution plan for its eligible U.S. based employees (the “Savings Plan”). The Company’s contribution to the Savings Plan was limited to 3.5% of an employee’s wages depending upon the employee’s level of voluntary wage deferral into the Savings Plan and was subject to annual review by the Board of Directors of SEACOR Holdings. For the year ended December 31, 2015 , the Company’s contribution to the Savings Plan was $1.3 million . 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 MNOPF and the MNRPF. The Company’s participation in the MNOPF and MNRPF began with the acquisition of the Stirling group of companies in 2001 and relates to the current and former employment of certain officers and ratings by the Company and/or Stirling’s predecessors from 1978 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 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. Prior to 2015, the Company was invoiced and expensed $0.4 million for its allocated share of the then cumulative funding deficits. On February 25, 2015, the High Court approved a new deficit contribution scheme, whereby any funding deficit of the MNRPF is to be remedied through funding contributions from all participating current and former employers, in a manner similar to the operation of the MNOPF. Based on an actuarial valuation in 2014, the potential cumulative funding deficit of the MNRPF was $491.7 million ( £325.0 million ). On August 28, 2015, the Company was invoiced and recognized payroll related operating expenses of $6.9 million ( £4.5 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. The invoiced amounts are payable in four installments, beginning in October 2015. Other Plans. Certain employees participate in other defined contribution plans in various international regions including the United Kingdom and Singapore. During the years ended December 31, 2017 , 2016 and 2015 , the Company incurred costs of $0.7 million per annum in the aggregate related to these plans, primarily from employer matching contributions.

Share Based Compensation

Share Based Compensation	12 Months Ended
	Dec. 31, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Share Based Compensation	14. SHARE BASED COMPENSATION 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 is equal to 10% of the total number shares of SEACOR Marine Common Stock. 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. As of December 31, 2017, a total of 1,556,300 shares remained available for issuance under the 2017 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 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 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 and received SEACOR Marine restricted stock from the Spin-off distribution in connection with outstanding SEACOR Holdings restricted stock held. As a consequence, 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 (see Note 15). 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 during the year ended December 31, 2017 : Director Stock Awards Granted 3,000 Restricted Stock Activity: Outstanding as of the beginning of year — Granted - 2017 Plan 1,000 Distributed by SEACOR Holdings in connection with the Spin-off 120,693 Vested — Forfeited — Outstanding as of the end of year 121,693 Stock Option Activity: Outstanding as of the beginning of year — Granted - 2017 Plan 613,700 Exercised — Forfeited — Expired — Outstanding as of the end of year 613,700 During the year ended December 31, 2017 , the Company recognized $0.8 million of compensation expense related to stock awards, restricted stock and stock options granted to employees and directors under the 2017 Plan and $0.6 million of compensation expense related to SEACOR Marine restricted stock distributed to employees by SEACOR Holdings in connection with the Spin-off (collectively referred to as “share awards”). As of December 31, 2017 , the Company had approximately $5.2 million in total unrecognized compensation costs of which $1.7 million and $1.4 million are expected to be recognized in 2018 and 2019, respectively, with the remaining balance recognized through 2021. The weighted average value of restricted stock granted under the 2017 Plan was $12.50 for the year ended December 31, 2017 . The weighted average value and exercise price of stock options granted under the 2017 Plan was $6.41 and $12.50 , respectively, for the year ended December 31, 2017 . The fair value of each option granted during the year ended December 31, 2017 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 52.5% ; (c) weighted average discount rate of 2.22% and (d) expected life of 6.00 years. As of December 31, 2017 , the weighted average remaining contractual term for total outstanding stock options was 9.90 years. As of December 31, 2017 , there was no aggregate intrinsic value of options outstanding.

Related Party Transactions

Related Party Transactions	12 Months Ended
	Dec. 31, 2017
Related Party Transactions [Abstract]
Related Party Transactions	15. RELATED PARTY TRANSACTIONS The Company provided services of $0.1 million to SEACOR Holdings during each of the years ended December 31, 2017, 2016 and 2015 . On December 1, 2015, the Company purchased a third party note receivable from SEACOR Holdings secured by offshore marine equipment for $13.6 million (see Note 6). On December 1, 2015, the Company purchased $36.6 million of marketable securities from 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, 2017, SEACOR Holdings has guaranteed $69.1 million for various obligations of the Company, including: BNDES Equipment Construction Finance Notes (see Note 7); letters of credit issued on behalf of the Company; performance obligations under sale-leaseback arrangements (see Note 16); and invoiced amounts for funding deficits under the MNOPF (see Note 13). Pursuant to a Transition Services Agreement with SEACOR Holdings, SEACOR Holdings charges the Company a fee of 0.5% on outstanding guaranteed amounts, which declines as the guaranteed obligations are settled by the Company. The Company recognized guarantee fees in connection with sale-leaseback arrangements of $0.3 million , $0.4 million and $0.1 million during 2017, 2016 and 2015, respectively, as additional leased-in equipment operating expenses in the accompanying consolidated statements of loss. Guarantee fees paid to SEACOR Holdings for all other obligations are recognized as SEACOR Holdings guarantee fees in the accompanying consolidated statements of loss. Pursuant to one of the Transitions Services Agreements with SEACOR Holdings, the Company is obligated to reimburse SEACOR Holdings up to 50% of the severance and restructuring costs actually incurred by SEACOR Holdings as a result of the Spin-off up to, but not in excess of, $6.0 million (such that the Company shall not be obligated to pay more than $3.0 million ). As of December 31, 2017, the Company has reimbursed SEACOR Holdings severance and restructuring costs of $0.7 million recognized as additional administrative and general expenses in the accompanying condensed consolidated statements of loss. Immediately preceding the Spin-off and pursuant to an Investment Agreement dated November 30, 2015 with the holders of the 3.75% Convertible Senior Notes, the Company reimbursed SEACOR Holdings for the final settlement of non-deductible Spin-off related expenses of $3.4 million recognized as additional administrative and general expenses in the accompanying condensed consolidated statements of loss. 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 continues to be supported by SEACOR Holdings for corporate services for a net fee of $6.3 million per annum pursuant to the Transition Services Agreements with SEACOR Holdings. For the year ended December 31, 2017, the Company incurred fees of $3.3 million for these services that were recognized as additional administrative and general expenses in the accompanying consolidated statements of loss. The fees incurred will decline as the services and functions provided by SEACOR Holdings are terminated and replicated within the Company. Prior to the Spin-off, certain costs and expenses of the Company were borne by SEACOR Holdings and charged to the Company. These costs and expenses are included in both operating and administrative and general expenses in the accompanying consolidated statements of loss and are summarized as follows for the years ended December 31 (in thousands): 2017 2016 2015 Payroll costs for SEACOR Holdings personnel assigned to the Company $ — $ — $ 57,939 Participation in SEACOR Holdings employee benefit plans 899 3,702 7,249 Participation in SEACOR Holdings defined contribution plan — — 1,876 Participation in SEACOR Holdings share award plans 8,383 4,588 4,730 Shared services allocation for administrative support 1,932 4,365 6,306 $ 11,214 $ 12,655 $ 78,100 • Actual payroll costs of SEACOR Holdings personnel assigned to the Company were charged to the Company. On January 1, 2016, the Company hired all of its employees directly and no longer had seconded personnel from SEACOR Holdings. • SEACOR Holdings maintained self-insured health benefit plans for participating employees, including those of the Company, and charged the Company for its share of total plan costs incurred based on the percentage of its participating employees. Following the Spin-off, the Company no longer participates in SEACOR Holdings’ self-insured health benefit plans. • SEACOR Holdings provided a defined contribution plan for participating U.S. employees, including those of the Company, and charged the Company for its share of employer matching contributions, which was limited to 3.5% of an employee’s wages depending upon the employee’s level of voluntary wage deferral contributed to the plan. On January 1, 2016, the Company’s eligible U.S. based employees were transferred to the SEACOR Marine 401(k) Plan. • Certain officers and employees of the Company received compensation through participation in SEACOR Holdings’ share award plans. The Company paid SEACOR Holdings for the fair value of its employees’ share awards. Pursuant to the Employee Matters Agreement with SEACOR Holdings, participating Company personnel vested in all outstanding SEACOR Holdings share awards upon the Spin-off and received SEACOR Marine restricted stock from the Spin-off distribution in connection with outstanding SEACOR Holdings restricted stock held. As a consequence, the Company paid SEACOR Holdings $9.4 million upon completion of the Spin-off, including $2.7 million for the distribution of 120,693 shares of SEACOR Marine restricted stock (see Note 14), which is being amortized over the participants’ remaining original vesting periods, and $6.7 million on the accelerated vesting of SEACOR Holdings share awards, which was immediately recognized. In addition, the Company recognized and paid share award expense of $1.7 million through the date of the Spin-off. • Prior to the Spin-off, SEACOR Holdings provided certain administrative support services to the Company under a shared services arrangement, including but not limited to payroll processing, information systems support, benefit plan management, cash disbursement support and treasury management. The Company was charged for its share of actual costs incurred generally based on volume processed or units supported. Prior to the Spin-off, SEACOR Holdings incurred various corporate costs in connection with providing certain corporate services, including, but not limited to, executive oversight, risk management, legal, accounting and tax, and charged quarterly management fees to the Company in order to fund its corporate overhead to cover such costs. Total management fees charged by SEACOR Holdings to the Company included actual corporate costs incurred plus a mark-up and were generally allocated within the consolidated group using income-based performance metrics reported by an operating segment in relation to SEACOR Holding’s other operating segments. On November 30, 2015, contemporaneously with the issuance of the 3.75% Convertible Senior Notes, the Company and SEACOR Holdings entered into an agreement for SEACOR Holdings to provide these services at a fixed rate of $7.7 million per annum beginning December 1, 2015 until the Spin-off. The Company’s incurred management fees from SEACOR Holdings were settled on a monthly basis and reported as SEACOR Holdings management fees in the accompanying consolidated statements of loss. Prior to the Company’s issuance of its 3.75% Convertible Senior Notes on December 1, 2015, the Company participated in a cash management program whereby certain operating and capital expenditures of the Company were funded through advances from SEACOR Holdings and certain cash collections of the Company were forwarded to SEACOR Holdings. Net amounts under this program were reported as advances from SEACOR Holdings in the accompanying consolidated balance sheets. The Company earned interest income on outstanding advances to SEACOR Holdings and incurred interest expense on outstanding advances from SEACOR Holdings, both being reported in the accompanying consolidated statements of loss as interest expense on advances and notes with SEACOR Holdings, net. Interest was calculated and settled on a quarterly basis using interest rates set at the discretion of SEACOR Holdings. SEACOR Holdings also issued notes to fund the working capital needs or acquisitions of the Company, generally to the Company’s international entities. The terms of these notes varied including periodic principal and interest payments, periodic interest only payments with balloon principal payment due at maturity, or balloon principal and interest payments due at maturity. As circumstances warrant, SEACOR Holdings had changed or extended the terms of these notes at its discretion. Interest expense incurred under these arrangements is included in the accompanying consolidated statements of loss as interest expense on advances and notes with SEACOR Holdings, net. All of the Company’s notes payable due SEACOR Holdings were settled during the year ended December 31, 2015. Charles Fabrikant (Non-Executive Chairman of SEACOR Marine), John Gellert (President, Chief Executive Officer and Director of SEACOR Marine), other members of the Company’s management and board of directors and other unaffiliated individuals indirectly invested in OSV Partners by purchasing interests from two unaffiliated limited partners of OSV Partners who wished to dispose of their interests. As of December 31, 2017, limited liability companies controlled by management and directors of the Company had invested $1.5 million , or 3.9% , and $0.3 million , or 5.0% , in the limited partner interests and preferred interests of OSV Partners, respectively. As of December 31, 2017, the investments of Messrs. Fabrikant and Gellert in such limited liability companies were $0.3 million each, representing 30.4% of such limited liability companies’ membership interests. The Company owns 30.4% and 38.6% in the limited partner interests and preferred interests of OSV Partners, respectively. The general partner of OSV Partners is a joint venture managed by the Company and an unaffiliated third party.

Commitments And Contingencies

Commitments And Contingencies	12 Months Ended
	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Commitments And Contingencies	16. COMMITMENTS AND CONTINGENCIES As of December 31, 2017 , the Company had capital commitments of $66.7 million that included four fast support vessels, three supply vessels and two wind farm utility vessels. The delivery dates and payment of certain costs (originally scheduled for payment in 2018, 2019 and 2020) for two of the fast support vessels are uncertain as the Company, at its option, may defer their construction for an indefinite period of time. The Company’s capital commitments by year of expected payment are as follows (in thousands): 2018 $ 13,435 2019 21,919 2020 10,696 Deferred (estimated based on current construction pricing) 20,697 $ 66,747 Subsequent to December 31, 2017, the Company committed an additional $11.0 million ( $10.1 million to be paid in 2018 and $0.9 million to be paid in 2019) to acquire two additional wind farm utility vessels and convert two of its existing supply vessels to a standby safety configuration. 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 growth prospects. As of December 31, 2017, the Company leases seven offshore support vessels and certain facilities and other equipment. These leasing agreements have been classified as operating leases for financial reporting purposes and related rental fees are charged to expense over the lease terms. The leases generally contain purchase and lease renewal options or rights of first refusal with respect to the sale or lease of the equipment. The lease terms range in duration from one to four years. Certain of the equipment leases are the result of sale-leaseback transactions with finance companies and certain of the gains arising from such sale-leaseback transactions have been deferred in the accompanying consolidated balance sheets and are being amortized as reductions in rental expense over the lease terms (see Note 1). Total rental expense for the Company’s operating leases in 2017 , 2016 and 2015 totaled $14.5 million , $19.4 million and $24.5 million , respectively. Future minimum payments in the years ended December 31 under operating leases that have a remaining term in excess of one year as of December 31, 2017 were as follows (in thousands): 2018 $ 16,525 2019 16,525 2020 13,460 2021 6,143 2022 6

Major Customers And Segment Inf

Major Customers And Segment Information	12 Months Ended
	Dec. 31, 2017
Segment Reporting [Abstract]
Major Customers And Segment Information	17. MAJOR CUSTOMERS AND SEGMENT INFORMATION During the years ended December 31, 2017 and 2016, Perenco UK Limited was responsible for $26.8 million or 15.2% and $28.4 million or 13.2% , respectively, of the Company’s total consolidated operating revenues. During the year ended December 31, 2015 , no single customer was responsible for more than 10% of the Company’s operating revenues. During the years ended December 31, 2017 , 2016 and 2015 , the ten largest customers of the Company accounted for approximately 59% , 58% and 55% , respectively, of the Company’s operating revenues. 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, 2017 , 2016 and 2015 , approximately 87% , 85% and 68% , respectively, of the Company’s operating revenues and $1.9 million , $(4.2) million and $8.6 million , respectively, of equity in earnings (losses) from 50% or less owned companies, net of tax, were derived from its 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 Brazil, Mexico, Central and South America Europe (primarily North Sea) Total For the year ended December 31, 2017 Operating Revenues: Time charter $ 18,079 $ 32,866 $ 33,410 $ 2,977 $ 73,213 $ 160,545 Bareboat charter — — — 4,636 — 4,636 Other 4,217 1,080 474 552 2,279 8,602 22,296 33,946 33,884 8,165 75,492 173,783 Direct Costs and Expenses: Operating: Personnel 15,621 13,419 16,883 809 34,768 81,500 Repairs and maintenance 3,594 5,957 9,037 274 8,793 27,655 Drydocking 1,828 2,180 968 — 4,059 9,035 Insurance and loss reserves 3,286 677 1,444 316 801 6,524 Fuel, lubes and supplies 1,485 2,815 3,727 223 3,782 12,032 Other 249 3,319 5,240 117 980 9,905 26,063 28,367 37,299 1,739 53,183 146,651 Direct Vessel Profit (Loss) $ (3,767 ) $ 5,579 $ (3,415 ) $ 6,426 $ 22,309 27,132 Other Costs and Expenses: Operating: Leased-in equipment $ 8,152 $ 3,870 $ 862 $ — $ 64 12,948 Administrative and general 56,217 Depreciation and amortization $ 22,060 $ 9,280 $ 17,724 $ 3,608 $ 10,107 62,779 131,944 Losses on Asset Dispositions and Impairments, Net (23,547 ) Operating Loss $ (128,359 ) As of December 31, 2017 Property and Equipment: Historical cost $ 410,475 $ 192,600 $ 326,378 $ 72,484 $ 177,899 $ 1,179,836 Accumulated depreciation (230,636 ) (57,228 ) (100,435 ) (37,281 ) (134,580 ) (560,160 ) $ 179,839 $ 135,372 $ 225,943 $ 35,203 $ 43,319 $ 619,676 United States (primarily Gulf of Mexico) Africa (primarily West Africa) Middle East and Asia Brazil, Mexico, Central and South America Europe (primarily North Sea) Total For the year ended December 31, 2016 Operating Revenues: Time charter $ 28,902 $ 36,706 $ 41,657 $ 196 $ 78,866 $ 186,327 Bareboat charter — — — 8,833 — 8,833 Other 3,954 856 12,230 1,180 2,256 20,476 32,856 37,562 53,887 10,209 81,122 215,636 Direct Costs and Expenses: Operating: Personnel 22,305 12,628 18,381 2,117 39,713 95,144 Repairs and maintenance 2,721 2,628 6,426 232 9,275 21,282 Drydocking 228 1,098 2,117 — 4,378 7,821 Insurance and loss reserves 3,363 539 731 43 1,006 5,682 Fuel, lubes and supplies 1,392 2,512 4,215 21 3,948 12,088 Other 271 2,519 3,247 114 1,180 7,331 30,280 21,924 35,117 2,527 59,500 149,348 Direct Vessel Profit $ 2,576 $ 15,638 $ 18,770 $ 7,682 $ 21,622 66,288 Other Costs and Expenses: Operating: Leased-in equipment $ 7,975 $ 3,898 $ 4,389 $ 913 $ 402 17,577 Administrative and general 49,308 Depreciation and amortization $ 27,052 $ 6,720 $ 11,550 $ 4,083 $ 8,664 58,069 124,954 Losses on Asset Dispositions and Impairments, Net (116,222 ) Operating Loss $ (174,888 ) As of December 31, 2016 Property and Equipment: Historical cost $ 404,226 $ 136,428 $ 197,389 $ 57,744 $ 162,972 $ 958,759 Accumulated depreciation (233,075 ) (60,794 ) (97,433 ) (34,455 ) (114,862 ) (540,619 ) $ 171,151 $ 75,634 $ 99,956 $ 23,289 $ 48,110 $ 418,140 United States (primarily Gulf of Mexico) Africa (primarily West Africa) Middle East and Asia Brazil, Mexico, Central and South America Europe (primarily North Sea) Total For the year ended December 31, 2015 Operating Revenues: Time charter $ 111,892 $ 53,724 $ 48,541 $ 17,585 $ 99,148 $ 330,890 Bareboat charter — — — 8,598 — 8,598 Other 6,859 3,528 14,951 1,602 2,440 29,380 118,751 57,252 63,492 27,785 101,588 368,868 Direct Costs and Expenses: Operating: Personnel 52,843 15,677 20,614 7,406 54,066 150,606 Repairs and maintenance 8,697 4,692 8,678 1,237 13,067 36,371 Drydocking 6,430 757 1,275 1,859 7,460 17,781 Insurance and loss reserves 5,193 1,165 1,448 535 1,557 9,898 Fuel, lubes and supplies 6,785 2,705 5,033 673 5,566 20,762 Other 4,456 4,085 7,316 849 1,339 18,045 84,404 29,081 44,364 12,559 83,055 253,463 Direct Vessel Profit $ 34,347 $ 28,171 $ 19,128 $ 15,226 $ 18,533 115,405 Other Costs and Expenses: Operating: Leased-in equipment $ 10,891 $ 4,695 $ 4,364 $ 2,545 $ 14 22,509 Administrative and general 53,085 Depreciation and amortization $ 26,605 $ 8,580 $ 11,209 $ 5,623 $ 9,712 61,729 137,323 Losses on Asset Dispositions and Impairments, Net (17,017 ) Operating Loss $ (38,935 ) As of December 31, 2015 Property and Equipment: Historical cost $ 447,862 $ 144,880 $ 218,927 $ 87,612 $ 203,338 $ 1,102,619 Accumulated depreciation (198,556 ) (71,965 ) (88,722 ) (48,303 ) (139,416 ) (546,962 ) $ 249,306 $ 72,915 $ 130,205 $ 39,309 $ 63,922 $ 555,657 The Company’s investments in 50% or less owned companies, which are accounted for under the equity method, also contribute to its consolidated results of operations. As of December 31, 2017 , the Company’s investments, at equity and advances to 50% or less owned companies in MexMar and its other 50% or less owned companies were $61.0 million and $31.2 million , respectively (see Note 4). Equity in earnings (losses) of 50% or less owned companies, net of tax for the years ended December 31 were as follows (in thousands): 2017 2016 2015 MexMar $ 10,103 $ 3,556 $ 5,650 Other (6,026 ) (9,870 ) 3,107 $ 4,077 $ (6,314 ) $ 8,757

Supplemental Information For St

Supplemental Information For Statements Of Cash Flows	12 Months Ended
	Dec. 31, 2017
Supplemental Cash Flow Information [Abstract]
Supplemental Information For Statements Of Cash Flows	18. SUPPLEMENTAL INFORMATION FOR STATEMENTS OF CASH FLOWS Supplemental information for the years ended December 31 was as follows (in thousands): 2017 2016 2015 Income taxes refunded, net $ 33,773 $ 10,224 $ 1,667 Interest paid, excluding capitalized interest 9,216 2,698 22,407 Schedule of Non-Cash Investing and Financing Activities: Exchange of receivable for investment in 50% or less owned company 1,000 — — Services received to settle notes receivable — — 2,500 Equipment received to settle notes receivable — 11,900 — Financial support from SEACOR Holdings upon issuance of the Company’s convertible senior notes — — 8,511

Quarterly Financial Information

Quarterly Financial Information	12 Months Ended
	Dec. 31, 2017
Quarterly Financial Data [Abstract]
Quarterly Financial Information	19. QUARTERLY FINANCIAL INFORMATION (UNAUDITED) Selected financial information for interim quarterly periods is presented below (in thousands, except share data). Earnings 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, 2017 Operating Revenues $ 49,343 $ 47,813 $ 42,323 $ 34,304 Operating Loss (35,830 ) (29,129 ) (44,815 ) (18,585 ) Net Income (Loss) 27,904 (22,356 ) (36,489 ) (7,599 ) Net Income (Loss) attributable to SEACOR Marine Holdings Inc. 28,961 (20,475 ) (33,992 ) (7,395 ) Basic Income (Loss) Per Common Share of SEACOR Marine Holdings Inc. $ 1.65 $ (1.17 ) $ (1.93 ) $ (0.42 ) Diluted Income (Loss) Per Common Share of SEACOR Marine Holdings Inc. $ 1.20 $ (1.25 ) $ (1.93 ) $ (0.42 ) 2016 Operating Revenues $ 44,361 $ 54,125 $ 57,271 $ 59,879 Operating Loss (82,719 ) (41,068 ) (34,514 ) (16,587 ) Net Loss (61,774 ) (28,007 ) (30,789 ) (12,580 ) Net Loss attributable to SEACOR Marine Holdings Inc. (61,575 ) (27,933 ) (30,580 ) (11,959 ) Basic and Diluted Loss Per Common Share of SEACOR Marine Holdings Inc. $ (3.48 ) $ (1.58 ) $ (1.73 ) $ (0.68 )

Valuation And Qualifying Accoun

Valuation And Qualifying Accounts	12 Months Ended
	Dec. 31, 2017
Valuation and Qualifying Accounts [Abstract]
Valuation And Qualifying Accounts	Description Balance Beginning of Year Charges (Recoveries) to Cost and Expenses Deductions (1) Balance End of Year Year Ended December 31, 2017 Allowance for doubtful accounts (deducted from trade and notes receivable) $ 5,359 $ (1,283 ) $ (37 ) $ 4,039 Year Ended December 31, 2016 Allowance for doubtful accounts (deducted from trade and notes receivable) $ 1,177 $ 4,280 $ (98 ) $ 5,359 Year Ended December 31, 2015 Allowance for doubtful accounts (deducted from trade and notes receivable) $ 1,177 $ — $ — $ 1,177 ______________________ (1) Trade receivable amounts deemed uncollectible that were removed from accounts receivable and allowance for doubtful accounts.

Nature Of Operations And Acco27

Nature Of Operations And Accounting Policies (Policy)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Nature Of Operations and Segmentation	Nature of Operations and Segmentation. The consolidated financial statements include the accounts of SEACOR Marine Holdings Inc. (“SEACOR Marine”) and its consolidated subsidiaries (collectively referred to as the “Company”). The Company provides global marine and support transportation services to offshore oil and natural gas exploration, development and production 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. 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. The Company has identified the following five principal geographic regions as its reporting segments: United States, primarily Gulf of Mexico. The Company’s vessels in this market support deepwater anchor handling, fast cargo transport, general cargo transport, well intervention, work-over, decommissioning, and diving operations. Africa, primarily West Africa. The Company’s vessels in this area generally support projects for major oil companies, primarily in Angola. Other vessels in this region operate in the Republic of the Congo and Mauritania. Middle East and Asia. The Company’s vessels in this area generally support exploration, personnel transport and seasonal construction activities in Azerbaijan, Egypt, Israel, Indonesia, India and countries along the Arabian Gulf and Arabian Sea, such as Saudi Arabia, the United Arab Emirates and Qatar. Brazil, Mexico, Central and South America. Through the Company’s 49% noncontrolling interest in Mantenimiento Express Maritimo, S.A.P.I. de C.V. (“MexMar”), the Company’s vessels in Mexico provide support for exploration and production activities in Mexico. In addition, the Company has vessels in Brazil. From time to time, the Company’s vessels have worked in Trinidad and Tobago, Guyana, Colombia and Venezuela. Europe, primarily North Sea. Demand for standby services developed in 1991 after the United Kingdom passed legislation requiring offshore operators to maintain higher specification standby safety vessels. The legislation requires a vessel to “stand by” to provide a means of evacuation and rescue for platform and rig personnel in the event of an emergency at an offshore installation. In addition, through the Company’s 87.5% controlling interest in Windcat Workboats Holdings Limited (“Windcat Workboats”), the owner of the wind farm utility fleet, the Company supports the construction and maintenance of offshore wind turbines. In the past, the Company has operated supply and anchor handling towing supply vessels in this region. The Spin-off. SEACOR Marine was previously a subsidiary of SEACOR Holdings Inc. (along with its consolidated subsidiaries, other than SEACOR Marine, collectively referred to as “SEACOR Holdings”). On June 1, 2017, SEACOR Holdings completed a spin-off of SEACOR Marine by way of a pro rata dividend of SEACOR Marine’s Common Stock, all of which was then held by SEACOR Holdings, to SEACOR Holdings’ shareholders of record as of May 22, 2017 (the “Spin-off”). SEACOR Marine entered into certain agreements with SEACOR Holdings to 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. Immediately following the Spin-off, SEACOR Marine began to operate as an independent, publicly traded company.
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 employs the cost method of accounting for investments in 50% or less owned companies it does not control or exercise significant influence. These investments in private companies are carried at cost and are adjusted only for capital distributions and other-than-temporary declines in fair value.
Use Of Estimates	Use of Estimates. The preparation of financial statements in conformity with accounting principles generally accepted in the United States 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 doubtful accounts, 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 recognizes revenue when it is realized or realizable and earned. Revenue is realized or realizable and earned when persuasive evidence of an arrangement exists, delivery has occurred or services have been rendered, the price to the buyer is fixed or determinable, and collectability is reasonably assured. Revenue that does not meet these criteria is deferred until the criteria are met. Deferred revenues for the years ended December 31 were as follows (in thousands): 2017 2016 2015 Balance at beginning of year $ 6,953 $ 6,953 $ 6,794 Revenues deferred during the year 4,699 — 159 Revenues recognized during the year (1,548 ) — — Balance at end of year $ 10,104 $ 6,953 $ 6,953 As of December 31, 2017 , the Company deferred revenues of $6.8 million related to the time charter of several offshore support vessels scheduled to be paid through the conveyance of an overriding royalty interest (the “Conveyance”) in developmental oil and natural gas producing properties operated by a customer in the U.S. Gulf of Mexico. Payments under the Conveyance, and the timing of such payments, were contingent upon production and energy sale prices. On August 17, 2012, the customer filed a voluntary petition for Chapter 11 bankruptcy. The Company is vigorously defending its interest in connection with the bankruptcy filing; however, payments received under the Conveyance subsequent to May 19, 2012 are subject to creditors’ claims in bankruptcy court. The Company will recognize revenues when reasonably assured of a judgment in its favor. All costs and expenses related to these charters were recognized as incurred. As of December 31, 2017, the Company deferred revenues of $3.2 million related to the time charter of an offshore support vessel to a customer from which collection was not reasonably assured. The Company will recognize revenues when collected or when collection is reasonably assured. All costs and expenses related to this charter were recognized as incurred. The Company earns revenues primarily from the time charter and bareboat charter of vessels to customers based upon daily rates of hire. Therefore, 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 all risk 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 whereby 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. Contract or charter durations may range from several days to several years. Longer duration charters are more common where equipment is not as readily available or specific equipment is required. In the North Sea, multi-year charters have been more common and constitute a significant portion of that market. Time charters in Asia have historically been less common and generally contracts or charters have terms of less than two years. In the Company’s other operating areas, charters vary in length from short-term to multi-year periods, many with cancellation clauses and no early termination penalty. 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 actually contracted to provide services to a particular customer.
Restricted Cash	Restricted Cash. Restricted cash primarily related to banking facility requirements.
Marketable Securities	Marketable Securities. Marketable equity securities with readily determinable fair values and debt securities are reported in the accompanying consolidated balance sheets as marketable securities. These investments are stated at fair value, as determined by their market observable prices, with both realized and unrealized gains and losses reported in the accompanying consolidated statements of loss as marketable security losses, net. Short sales of marketable securities are stated at fair value in the accompanying consolidated balance sheets with both realized and unrealized losses reported in the accompanying consolidated statements of loss as marketable security gains (losses), net. Marketable securities are classified as trading securities for financial reporting purposes with gains and losses reported as operating activities in the accompanying consolidated statements of cash flows.
Trade Receivables	Trade and Other Receivables. Customers are primarily major integrated national and international oil companies and large independent oil and natural gas exploration and production companies. Trade customers are granted credit on a short-term basis and related credit risks are considered minimal. Other receivables consist primarily of operating expenses incurred by the Company related to vessels it manages for others and insurance and income tax receivables. The Company routinely reviews its receivables and makes provisions for probable doubtful accounts; however, those provisions are estimates and actual results could differ from those estimates and those differences may be material. Trade receivables are deemed uncollectible and removed from accounts receivable and the allowance for doubtful accounts 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. There were no inventory write-downs during the years ended December 31, 2017 , 2016 , and 2015 .
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, 2017 , 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: Wind farm utility vessels 10 All other offshore support vessels (excluding wind farm utility) 20 The Company’s property and equipment as of December 31 was as follows (in thousands): Historical Cost (1) Accumulated Depreciation Net Book Value 2017 Offshore support vessels: Anchor handling towing supply $ 198,222 $ (174,159 ) $ 24,063 Fast support 424,865 (89,980 ) $ 334,885 Supply 105,360 (51,494 ) $ 53,866 Standby safety 118,414 (97,603 ) $ 20,811 Specialty 30,529 (19,304 ) $ 11,225 Liftboats 196,504 (54,161 ) $ 142,343 Wind farm utility 65,976 (40,358 ) $ 25,618 General machinery and spares 14,385 (13,244 ) $ 1,141 Other (2) 25,581 (19,857 ) $ 5,724 $ 1,179,836 $ (560,160 ) $ 619,676 2016 Offshore support vessels: Anchor handling towing supply $ 228,857 $ (183,757 ) $ 45,100 Fast support 251,415 (72,599 ) $ 178,816 Supply 96,774 (58,028 ) $ 38,746 Standby safety 109,436 (88,020 ) $ 21,416 Specialty 45,765 (24,063 ) $ 21,702 Liftboats 104,356 (45,447 ) $ 58,909 Wind farm utility 60,671 (29,019 ) $ 31,652 General machinery and spares 32,921 (20,008 ) $ 12,913 Other (2) 28,564 (19,678 ) $ 8,886 $ 958,759 $ (540,619 ) $ 418,140 _____________________ (1) Includes property and equipment acquired in business acquisitions at acquisition date fair value, and net of the impact of recognized impairment charges. (2) Includes land, buildings, leasehold improvements, vehicles and other property and equipment. Depreciation expense totaled $62.8 million , $58.0 million and $60.8 million in 2017 , 2016 and 2015 , 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 $3.6 million , $7.0 million and $4.4 million in 2017 , 2016 and 2015 , respectively.
Intangible Assets	Intangible Assets. During the year ended December 31, 2016 , the Company wrote-off its intangible assets as part of recognized impairment charges associated with its liftboat fleet (see Impairment of Long-Lived Assets below). During the years ended 2016 and 2015 , the Company recognized amortization expense of $0.1 million and $0.9 million , respectively.
Impairment Of Long-Lived Assets	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 anchor handling towing supply 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, 2017, the Company recorded impairment charges of $27.5 million primarily associated with its anchor handling towing supply vessels, one leased-in supply vessel removed from service as it is not expected to be marketed prior to the expiration of its lease, one owned fast support vessel removed from service and two owned in-service specialty vessels. During the year ended December 31, 2016, the Company recorded impairment charges of $119.7 million primarily associated with its anchor handling towing supply fleet, its liftboat fleet and one specialty vessel. During the year ended December 31, 2015, the Company recorded impairment charges of $7.1 million primarily related to the suspended construction of two fast support vessels and the removal from service of one leased-in supply vessel. Estimated fair values for the Company’s owned vessels were established by independent appraisers and other market data such as recent sales of similar vessels (see Note 10). If market conditions further decline from the depressed utilization and rates per day worked experience over the last three years, fair values based on future appraisals could decline significantly. 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., fast support vessels), vessels required for customers to meet regulatory mandates and operating under multiple year contracts (e.g., standby safety vessels) or vessels that service customers outside of the offshore oil and natural gas market (e.g., wind farm utility vessels). For vessel classes and individual vessels with indicators of impairment but not recently impaired as of December 31, 2017, 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. During the years ended December 31, 2017 and 2016 , the Company recognized impairment charges of $8.8 million and $6.9 million , respectively, net of tax, related to its 50% or less owned companies (see Note 4). The Company did not recognize any impairment charges during the year ended December 31, 2015 .
Goodwill	Goodwill . Goodwill is recorded when the purchase price paid for an acquisition exceeds the fair value of net identified tangible and intangible assets acquired. During the year ended December 31, 2015 , the Company recognized a $13.4 million impairment charge
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 2).
Deferred Financing 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 is 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. Prior to the Spin-off, SEACOR Marine was included in the consolidated U.S. federal income tax return of SEACOR Holdings. 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.
Deferred Gains	Deferred Gains - Vessel Sale-Leaseback Transactions and Financed Vessel Sales . From time to time, the Company enters into vessel sale-leaseback transactions with finance companies or provides 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 is not immediately recognized in income and has been recorded in the accompanying consolidated balance sheets in deferred gains and other liabilities. In sale-leaseback transactions, gains are deferred to the extent of the present value of future minimum lease payments and are amortized as reductions to rental expense over the applicable lease terms. In financed vessel sales, gains are deferred to the extent that the repayment of purchase notes is dependent on the future operations of the sold vessels and are amortized based on cash received from the buyers. Deferred gain activity related to these transactions for the years ended December 31 was as follows (in thousands): 2017 2016 2015 Balance at beginning of year $ 32,035 $ 40,234 $ 50,934 Amortization of deferred gains included in operating expenses as reduction to rental expense (8,118 ) (8,199 ) (8,199 ) Amortization of deferred gains included in losses on asset dispositions and impairments, net — — (2,501 ) Other (364 ) — — Balance at end of year $ 23,553 $ 32,035 $ 40,234 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. Deferred gain activity related to these transactions for the years ended December 31 was as follows (in thousands): 2017 2016 2015 Balance at beginning of year $ 1,875 $ 3,064 $ 3,136 Amortization of deferred gains included in losses on asset dispositions and impairments, net — (36 ) (72 ) Other (422 ) (1,153 ) — Balance at end of year $ 1,453 $ 1,875 $ 3,064
Foreign Currency Translation And Transactions	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.
Earnings 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 assumes 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 3.75% Convertible Senior Notes. For the years ended December 31, 2017, 2016 and 2015, diluted loss per common share of the Company excluded 4,070,500 shares issuable upon the conversion of the 3.75% Convertible Senior Notes as the effect of their inclusion in the computation would be anti-dilutive or were contingent upon the Spin-off. In addition, for the year ended December 31, 2017, diluted loss per common share of the Company excluded 121,693 shares of restricted stock and 613,700 outstanding stock options as the effect of their inclusion in the computation would be anti-dilutive.
New Accounting Pronouncements	New Accounting Pronouncements. On May 28, 2014, the Financial Accounting Standards Board (“FASB”) issued a comprehensive new revenue recognition standard that will supersede nearly all existing revenue recognition guidance under generally accepted accounting principles in the United States. The core principal of the new standard is that a company will recognize revenue when it transfers promised goods or services to customers in an amount that reflects the consideration to which the company expects to be entitled in exchange for those goods or services. The Company will adopt the new standard on January 1, 2018 and expects to use the modified retrospective approach upon adoption. The Company has determined that adopting the new accounting standard will not have a material impact on its consolidated financial position, results of operations or cash flows for any of its revenue streams. On February 25, 2016, the FASB issued a comprehensive new leasing standard, which improves 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 will adopt the new standard on January 1, 2019 and will use the modified retrospective approach upon adoption. The Company expects the adoption of the new standard will have a material impact on its consolidated financial position, results of operations and cash flows, although it has not yet determined the extent of the impact. On August 26, 2016, the FASB issued an amendment to the accounting standard which amends or clarifies guidance on classification of certain transactions in the statement of cash flows, including classification of proceeds from the settlement of insurance claims, debt prepayments, debt extinguishment costs and contingent consideration payments after a business combination. The Company will adopt the new standard on January 1, 2018 and does not expect the adoption of the new standard will have a material impact on its consolidated financial position, results of operations or cash flows. 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 will adopt the new standard on January 1, 2018 and expects the impact of the adoption of the new standard to result in a reduction of $12.1 million to the Company’s opening retained earnings. On November 17, 2016, the FASB issued an amendment to the accounting standard which requires that restricted cash and restricted cash equivalents be included with cash and cash equivalents when reconciling the beginning-of-period and end-of-period total cash amounts shown on the statement of cash flows. The new standard is effective for fiscal years beginning after December 15, 2018. Early adoption is permitted. On January 5, 2017, the FASB issued an amendment to the accounting standard which clarifies the definition of a business and assists entities with evaluating whether transactions should be accounted for as acquisitions (or disposals) of assets or businesses. The Company will adopt the new standard on January 1, 2018 and does not expect the adoption of the new standard to have a material impact on its consolidated financial position, results of operations or cash flows. On February 22, 2017, the FASB issued an amendment to the accounting standard which clarifies the scope of guidance on nonfinancial asset derecognition and the accounting for partial sales of nonfinancial assets. The new guidance also conforms the derecognition guidance for nonfinancial assets with the model in the new revenue standard. The Company will adopt the new standard on January 1, 2018 and does not expect the adoption of the new standard to have a material impact on its consolidated financial position, results of operations or cash flows.

Nature Of Operations And Acco28

Nature Of Operations And Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Deferred Revenues Included In Other Current Liabilities	Deferred revenues for the years ended December 31 were as follows (in thousands): 2017 2016 2015 Balance at beginning of year $ 6,953 $ 6,953 $ 6,794 Revenues deferred during the year 4,699 — 159 Revenues recognized during the year (1,548 ) — — Balance at end of year $ 10,104 $ 6,953 $ 6,953
Schedule Of Estimated Useful Life Of Equipment	As of December 31, 2017 , 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: Wind farm utility vessels 10 All other offshore support vessels (excluding wind farm utility) 20 Deliveries of offshore support vessels for the years ended December 31 were as follows: 2017 2016 2015 Fast support 6 12 3 Supply 5 2 1 Specialty — 1 — Wind farm utility — 2 2 11 17 6 _____________________ (1) Excludes four fast support vessels acquired in the Sea-Cat Crewzer and Sea-Cat Crewzer II acquisitions and two liftboats on the consolidation of Falcon Global. Major equipment dispositions for the years ended December 31 were as follows: 2017 (1) 2016 2015 Fast support vessels — — 1 Standby safety 1 4 — Supply 1 5 1 Liftboats 2 — — 4 9 2 _____________________ (1) Excludes the sale of nine offshore support vessels previously removed from service.
Property Plant And Equipment By Major Class [Text Block]	The Company’s property and equipment as of December 31 was as follows (in thousands): Historical Cost (1) Accumulated Depreciation Net Book Value 2017 Offshore support vessels: Anchor handling towing supply $ 198,222 $ (174,159 ) $ 24,063 Fast support 424,865 (89,980 ) $ 334,885 Supply 105,360 (51,494 ) $ 53,866 Standby safety 118,414 (97,603 ) $ 20,811 Specialty 30,529 (19,304 ) $ 11,225 Liftboats 196,504 (54,161 ) $ 142,343 Wind farm utility 65,976 (40,358 ) $ 25,618 General machinery and spares 14,385 (13,244 ) $ 1,141 Other (2) 25,581 (19,857 ) $ 5,724 $ 1,179,836 $ (560,160 ) $ 619,676 2016 Offshore support vessels: Anchor handling towing supply $ 228,857 $ (183,757 ) $ 45,100 Fast support 251,415 (72,599 ) $ 178,816 Supply 96,774 (58,028 ) $ 38,746 Standby safety 109,436 (88,020 ) $ 21,416 Specialty 45,765 (24,063 ) $ 21,702 Liftboats 104,356 (45,447 ) $ 58,909 Wind farm utility 60,671 (29,019 ) $ 31,652 General machinery and spares 32,921 (20,008 ) $ 12,913 Other (2) 28,564 (19,678 ) $ 8,886 $ 958,759 $ (540,619 ) $ 418,140 _____________________ (1) Includes property and equipment acquired in business acquisitions at acquisition date fair value, and net of the impact of recognized impairment charges. (2) Includes land, buildings, leasehold improvements, vehicles and other property and equipment.
Schedule of Deferred Gains	Deferred gain activity related to these transactions for the years ended December 31 was as follows (in thousands): 2017 2016 2015 Balance at beginning of year $ 1,875 $ 3,064 $ 3,136 Amortization of deferred gains included in losses on asset dispositions and impairments, net — (36 ) (72 ) Other (422 ) (1,153 ) — Balance at end of year $ 1,453 $ 1,875 $ 3,064 Deferred gain activity related to these transactions for the years ended December 31 was as follows (in thousands): 2017 2016 2015 Balance at beginning of year $ 32,035 $ 40,234 $ 50,934 Amortization of deferred gains included in operating expenses as reduction to rental expense (8,118 ) (8,199 ) (8,199 ) Amortization of deferred gains included in losses on asset dispositions and impairments, net — — (2,501 ) Other (364 ) — — Balance at end of year $ 23,553 $ 32,035 $ 40,234
Schedule of Accumulated Other Comprehensive Income (Loss)	Accumulated Other Comprehensive Loss. The components of accumulated other comprehensive loss were as follows (in thousands): SEACOR Marine Holdings Inc. Stockholder’s Equity Noncontrolling Interests Foreign Currency Translation Adjustments Derivative Gains (Losses) on Cash Flow Hedges, net Total Foreign Currency Translation Adjustments Derivative Losses on Cash Flow Hedges, net Other Comprehensive Loss Year Ended December 31, 2014 $ (3,664 ) $ 19 $ (3,645 ) $ (87 ) $ — Other comprehensive loss (3,571 ) (198 ) (3,769 ) (442 ) — $ (4,211 ) Income tax benefit 1,250 69 1,319 — — 1,319 Year Ended December 31, 2015 (5,985 ) (110 ) (6,095 ) (529 ) — $ (2,892 ) Other comprehensive income (loss) (8,351 ) 286 (8,065 ) (1,085 ) (17 ) $ (9,167 ) Income tax (expense) benefit 2,923 (100 ) 2,823 — — 2,823 Year Ended December 31, 2016 (11,413 ) 76 (11,337 ) (1,614 ) (17 ) $ (6,344 ) Other comprehensive income 4,397 703 5,100 257 18 $ 5,375 Income tax expense (1) (6,179 ) (77 ) (6,256 ) — — (6,256 ) Year Ended December 31, 2017 $ (13,195 ) $ 702 $ (12,493 ) $ (1,357 ) $ 1 $ (881 ) ______________________ (1) For the year ended December 31, 2017, income tax expense included income tax provisions of $4.5 million recognized as a result of new U.S. tax legislation signed into law on December 22, 2017.

Business Acquisitions (Tables)

Business Acquisitions (Tables)	12 Months Ended
	Dec. 31, 2017
Business Combinations [Abstract]
Schedule of Business Acquisitions, by Acquisition [Table Text Block]	Purchase Price Allocation. The allocation of the purchase price for the Company’s acquisitions for the years ended December 31 was as follows (in thousands): 2017 2016 Restricted cash $ — $ 275 Trade and other receivables 235 1,250 Other current assets 4,148 — Investments, at Equity, and Advances to 50% or Less Owned Companies (15,700 ) — Property and Equipment 61,626 1,367 Accounts payable 747 199 Other current liabilities (76 ) — Long-Term Debt (41,186 ) (3,091 ) Other (43 ) — Purchase price (1) $ 9,751 $ — ______________________ (1) Purchase price in 2017 is net of cash acquired totaling $5.9 million .

Equipment Acquisitions And Disp

Equipment Acquisitions And Dispositions (Tables)	12 Months Ended
	Dec. 31, 2017
Disclosure Text Block [Abstract]
Property, Plant and Equipment Disclosure [Text Block]	3. EQUIPMENT ACQUISITIONS AND DISPOSITIONS Equipment Additions. The Company’s capital expenditures and payments on fair value derivative hedges were $69.4 million , $101.3 million and $87.8 million in 2017 , 2016 and 2015 , respectively. Deliveries of offshore support vessels for the years ended December 31 were as follows: 2017 2016 2015 Fast support 6 12 3 Supply 5 2 1 Specialty — 1 — Wind farm utility — 2 2 11 17 6 _____________________ (1) Excludes four fast support vessels acquired in the Sea-Cat Crewzer and Sea-Cat Crewzer II acquisitions and two liftboats on the consolidation of Falcon Global. Equipment Dispositions. During the year ended December 31, 2017 , the Company sold property and equipment for net proceeds of $11.2 million ( $10.7 million in cash and $0.5 million in cash deposits previously received) and gains of $3.9 million , all of which were recognized currently. In addition, the Company received $0.1 million in deposits on future property and equipment sales. During the year ended December 31, 2016 , the Company sold property and equipment for net proceeds of $41.4 million and gains of $3.5 million , all of which were recognized currently. In addition, the Company received $0.5 million in deposits on future property and equipment sales. During the year ended December 31, 2015 , the Company sold property and equipment for net proceeds of $15.7 million and gains of $0.9 million , all of which were recognized currently. In addition, the Company recognized previously deferred gains of $2.6 million . Major equipment dispositions for the years ended December 31 were as follows: 2017 (1) 2016 2015 Fast support vessels — — 1 Standby safety 1 4 — Supply 1 5 1 Liftboats 2 — — 4 9 2 _____________________ (1) Excludes the sale of nine offshore support vessels previously removed from service.
Property, Plant and Equipment [Table Text Block]	As of December 31, 2017 , 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: Wind farm utility vessels 10 All other offshore support vessels (excluding wind farm utility) 20 Deliveries of offshore support vessels for the years ended December 31 were as follows: 2017 2016 2015 Fast support 6 12 3 Supply 5 2 1 Specialty — 1 — Wind farm utility — 2 2 11 17 6 _____________________ (1) Excludes four fast support vessels acquired in the Sea-Cat Crewzer and Sea-Cat Crewzer II acquisitions and two liftboats on the consolidation of Falcon Global. Major equipment dispositions for the years ended December 31 were as follows: 2017 (1) 2016 2015 Fast support vessels — — 1 Standby safety 1 4 — Supply 1 5 1 Liftboats 2 — — 4 9 2 _____________________ (1) Excludes the sale of nine offshore support vessels previously removed from service.

Investments, At Equity, And A31

Investments, At Equity, And Advances To 50% Or Less Owned Companies (Tables)	12 Months Ended
	Dec. 31, 2017
Equity Method Investment, Summarized Financial Information [Abstract]
Summarized Financial Information For The Company's Investments, At Equity	Investments, at equity, and advances to 50% or less owned companies as of December 31 were as follows (in thousands): Ownership 2017 2016 MexMar 49.0% $ 60,980 $ 63,404 OSV Partners 30.4% 10,006 9,245 Nautical Power 50.0% 6,408 6,413 Dynamic Offshore Drilling 19.0% 4,958 15,871 Falcon Global 50.0% — 18,539 Sea Cat Crewzer II 50.0% — 11,246 Sea-Cat Crewzer 50.0% — 4,088 Other 20.0% — 50.0% 9,817 9,505 $ 92,169 $ 138,311 Equity in earnings (losses) of 50% or less owned companies, net of tax for the years ended December 31 were as follows (in thousands): 2017 2016 2015 MexMar $ 10,103 $ 3,556 $ 5,650 Other (6,026 ) (9,870 ) 3,107 $ 4,077 $ (6,314 ) $ 8,757
Business Acquisitions	2. BUSINESS ACQUISITIONS Sea-Cat Crewzer. On April 28, 2017, the Company acquired a 100% controlling interest in Sea-Cat Crewzer, which owns an operates two high-speed offshore catamarans, through the acquisition of its partners’ 50% ownership interest for $4.4 million in cash (see Note 4). The Company performed a fair value analysis and the purchase price was allocated to the acquired assets and liabilities based on their fair values resulting in no goodwill being recorded. Sea-Cat Crewzer II. On April 28, 2017, the Company acquired a 100% controlling interest in Sea-Cat Crewzer II, which owns and operates two high-speed offshore catamarans, through the acquisition of its partners’ 50% ownership interest for $11.3 million in cash (see Note 4). The Company performed a fair value analysis and the purchase price was allocated to the acquired assets and liabilities based on their fair values resulting in no goodwill being recorded. Cypress CKOR. On December 12, 2016, the Company obtained a 100% controlling interest in Cypress CKOR LLC (“Cypress CKOR”), an owner of one offshore support vessel, for one dollar and the assumption of $3.1 million in debt. The Company performed a fair value analysis and the purchase price was allocated to the acquired assets and liabilities based on their fair values resulting in no goodwill being recorded. Purchase Price Allocation. The allocation of the purchase price for the Company’s acquisitions for the years ended December 31 was as follows (in thousands): 2017 2016 Restricted cash $ — $ 275 Trade and other receivables 235 1,250 Other current assets 4,148 — Investments, at Equity, and Advances to 50% or Less Owned Companies (15,700 ) — Property and Equipment 61,626 1,367 Accounts payable 747 199 Other current liabilities (76 ) — Long-Term Debt (41,186 ) (3,091 ) Other (43 ) — Purchase price (1) $ 9,751 $ — ______________________ (1) Purchase price in 2017 is net of cash acquired totaling $5.9 million . The impact of consolidating Falcon Global’s net assets effective March 31, 2017 to the Company’s financial position was as follows (in thousands): Cash $ 1,943 Marketable securities 785 Trade and other receivables (291 ) Investments, at Equity, and Advances to 50% or Less Owned Companies (19,374 ) Property and Equipment 96,000 Accounts payable 3,201 Other current liabilities 1,153 Long-Term Debt 58,335 Other Liabilities (1,000 ) Noncontrolling interests in subsidiaries 17,374
Additional Financial Information Disclosure [Text Block]	Condensed Financial Information of MexMar. Summarized financial information of MexMar as of and for the years ended December 31 was as follows (in thousands): 2017 2016 Current assets $ 71,990 $ 50,996 Noncurrent assets 194,990 209,806 Current liabilities 23,931 23,089 Noncurrent liabilities 147,043 151,515 2017 2016 2015 Operating Revenues $ 67,003 $ 70,521 $ 78,363 Costs and Expenses: Operating and administrative 29,405 37,613 41,837 Depreciation 15,977 13,958 13,089 45,382 51,571 54,926 Operating Income $ 21,621 $ 18,950 $ 23,437 Net Income $ 9,233 $ 6,476 $ 15,638 Condensed Financial Information of Falcon Global, Sea-Cat Crewzer and Sea-Cat Crewzer II. Summarized financial information as of and for the years ended December 31 was as follows (in thousands): 2016 Current assets $ 14,834 Noncurrent assets 166,076 Current liabilities 9,624 Noncurrent liabilities 90,693 2017 (1) 2016 2015 Operating Revenues $ 5,075 $ 21,611 $ 24,439 Costs and Expenses: Operating and administrative 3,752 12,837 9,441 Depreciation 2,324 3,694 3,708 6,076 16,531 13,149 Operating Income (Loss) $ (1,001 ) $ 5,080 $ 11,290 Net Income (Loss) $ (2,699 ) $ 778 $ 6,468 _____________________ (1) Includes activity through date of acquisition or consolidation. Combined Condensed Financial Information of Other Investees (excluding MexMar, Falcon Global, Sea-Cat Crewzer and Sea-Cat Crewzer II). 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): 2017 2016 Current assets $ 61,360 $ 78,071 Noncurrent assets 247,038 255,270 Current liabilities 14,603 32,731 Noncurrent liabilities 138,789 158,628 2017 2016 2015 Operating Revenues $ 77,409 $ 77,571 $ 92,559 Costs and Expenses: Operating and administrative 46,748 51,136 57,922 Depreciation 12,198 13,181 13,961 58,946 64,317 71,883 Loss on Asset Dispositions and Impairments, Net — (21,323 ) (2,201 ) Operating Income $ 18,463 $ (8,069 ) $ 18,475 Net Income (Loss) $ 6,451 $ (19,229 ) $ 3,829

Long-Term Debt (Tables)

Long-Term Debt (Tables)	12 Months Ended
	Dec. 31, 2017
Long-term Debt, Unclassified [Abstract]
Schedule Of Company's Borrowings	The Company’s long-term debt obligations as of December 31 were as follows (in thousands): 2017 2016 3.75% Convertible Senior Notes $ 175,000 $ 175,000 Falcon Global Term Loan Facility 54,870 — Sea-Cat Crewzer III Term Loan Facility 29,078 22,785 Windcat Workboats Facilities 25,202 22,118 Sea-Cat Crewzer II Term Loan Facility 20,871 — Sea-Cat Crewzer Term Loan Facility 18,504 — C-Lift Acquisition Notes 16,000 17,500 BNDES Equipment Construction Finance Notes 7,234 9,186 Cypress CKOR Term Loan 1,300 2,452 348,059 249,041 Portion due within one year (22,858 ) (20,400 ) Debt discount (27,373 ) (4,567 ) Issue costs (5,787 ) (6,269 ) $ 292,041 $ 217,805
Schedule Of Long-Term Debt Maturities	The Company’s contractual long-term debt maturities for the years ended December 31 were as follows (in thousands): 2018 $ 22,858 2019 54,533 2020 10,358 2021 34,989 2022 208,618 Years subsequent to 2022 16,703 $ 348,059

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Schedule Of Income Before Income Tax, Domestic and Foreign	oss 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): 2017 2016 2015 United States $ (90,696 ) $ (169,523 ) $ (47,184 ) Foreign (45,112 ) (28,095 ) (1,963 ) Eliminations 18,785 7,313 (3,429 ) $ (117,023 ) $ (190,305 ) $ (52,576 )
Components Of Income Tax Expense (Benefit)	The components of income tax benefit for the years ended December 31 were as follows (in thousands): 2017 2016 2015 Current: Federal $ (16,705 ) $ (20,718 ) $ (6,814 ) State (42 ) (139 ) 420 Foreign 3,347 5,436 5,907 (13,400 ) (15,421 ) (487 ) Deferred: Federal (60,750 ) (47,692 ) (15,956 ) State (172 ) (446 ) (14 ) Foreign (84 ) 90 (516 ) (61,006 ) (48,048 ) (16,486 ) $ (74,406 ) $ (63,469 ) $ (16,973 )
Components 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: 2017 2016 2015 Statutory rate (35.0 )% (35.0 )% (35.0 )% U.S. federal income tax law changes (37.3 )% — % — % SEACOR Holdings share awards to Company personnel 2.3 % 0.4 % 0.1 % Non-deductible expenses 1.8 % 0.1 % 1.8 % Exclusion of foreign subsidiaries with accumulated losses 2.7 % 1.1 % 0.5 % Noncontrolling interests 1.7 % 0.2 % (0.5 )% State taxes (0.2 )% (0.3 )% 0.5 % Other 0.4 % 0.1 % 0.3 % (63.6 )% (33.4 )% (32.3 )%
Components Of The Net Deferred Income Tax Liabilities	The components of net deferred income tax liabilities as of December 31 were as follows (in thousands): 2017 2016 Deferred tax liabilities: Property and equipment $ 55,262 $ 98,654 Unremitted earnings of foreign subsidiaries — 24,084 Investments in 50% or Less Owned Companies 4,258 15,203 Other 5,901 2,260 Total deferred tax liabilities 65,421 140,201 Deferred tax assets: Federal Net Operating Loss Carryforwards 5,111 — Other 5,373 15,256 10,484 15,256 Valuation Allowance (569 ) — Total deferred tax assets 9,915 15,256 Net deferred tax liabilities $ 55,506 $ 124,945 As of December 31, 2017, the Company’s valuation allowance of $0.6 million related to various state net operating loss carryforwards. The estimated impact of the new U.S. tax legislation signed into law on December 22, 2017 is based on management’s current knowledge and assumptions. As of December 31, 2017, the Company’s federal net operating loss carryforwards excluded unrecognized tax benefits of $3.9 million as a result of uncertainty regarding the interpretation of the new tax law. The recognition of these unrecognized tax benefits, as well as any other items identified upon the Company’s further analysis of the new tax law, will affect the Company’s effective tax rate in future periods, which could be materially different from the current estimates recorded.

Derivative Instruments And He34

Derivative Instruments And Hedging Strategies (Tables)	12 Months Ended
	Dec. 31, 2017
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Fair Values Of Derivative Instruments	The fair values of the Company’s derivative instruments as of December 31 were as follows (in thousands): 2017 2016 Derivative (1) Derivative (2) Derivative (1) Derivative (2) Derivatives designated as hedging instruments: Forward currency exchange contracts (fair value hedges) $ — $ — $ — $ 316 Interest rate swap agreements (cash flow hedges) 260 20 — 73 260 20 — 389 Derivatives not designated as hedging instruments: Conversion option liability on 3.75% Convertible Senior Notes — 6,832 — — Forward currency exchange, option and future contracts — — 195 158 Interest rate swap agreements 159 46 — — $ 419 $ 6,898 $ 195 $ 547 _________________ (1) Included in other receivables in the accompanying consolidated balance sheets. (2) Included in other current liabilities in the accompanying consolidated balance sheets, except for the conversion option liability on the 3.75% Convertible Senior Notes.
Recognized Gains (Losses) On Derivative Instruments Not Designated As Hedging Instruments	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 2017 2016 2015 Conversion option liability on 3.75% Convertible Senior Notes $ 20,422 $ — $ — Interest rate swap agreements 46 (18 ) (18 ) Options on equities — 3,095 (2,748 ) Forward currency exchange, option and future contracts (212 ) (82 ) — $ 20,256 $ 2,995 $ (2,766 )

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Financial Assets And Liabilities Measured At Fair Value 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 2017 ASSETS Derivative instruments (included in other receivables) $ — $ 419 $ — Construction reserve funds 45,361 — — LIABILITIES Derivative instruments (included in other current liabilities) — 66 — Conversion Option Liability on 3.75% Convertible Senior Notes — — 6,832 2016 ASSETS Marketable securities $ 40,139 $ — $ — Derivative instruments (included in other receivables) — 195 — Construction reserve funds 78,209 — — LIABILITIES Derivative instruments (included in other current liabilities) — 547 —
Estimated Fair Value Of Other 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): Carrying Amount Estimated Fair Value Level 1 Level 2 Level 3 2017 ASSETS Cash, cash equivalents and restricted cash $ 112,551 $ 112,551 $ — $ — Investments, at cost, in 50% or less owned companies (included in other assets) 132 see below LIABILITIES Long-term debt, including current portion 314,899 — 291,932 — 2016 ASSETS Cash, cash equivalents and restricted cash $ 118,771 $ 118,771 $ — $ — Investments, at cost, in 50% or less owned companies (included in other assets) 132 see below LIABILITIES Long-term debt, including current portion 238,205 — 242,404 —
Non-Financial 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 2017 ASSETS Property and equipment: Anchor handling towing supply $ — $ 12,400 $ — Fast support — 175 — Specialty — 750 — Investments, at equity, in 50% or less owned companies — 20,658 20,430 2016 ASSETS Property and equipment: Anchor handling towing supply $ — $ 2,600 $ 42,500 Fast support — 50 — Supply — 2,153 1,800 Specialty — 4,000 — Liftboats — — 62,830 Investments, at equity, in 50% or less owned companies — — 18,539 Notes receivable from third parties (included in other assets) — — 11,900

Noncontrolling Interests in S36

Noncontrolling Interests in Subsidiaries Noncontrolling Interests (Tables)	12 Months Ended
	Dec. 31, 2017
Noncontrolling Interest [Abstract]
Redeemable Noncontrolling Interest [Table Text Block]	Noncontrolling interests in the Company’s consolidated subsidiaries as of December 31 were as follows (in thousands): Noncontrolling Interests 2017 2016 Falcon Global 50.0% $ 12,087 $ — Windcat Workboats 12.5% 2,608 5,266 Other 1.8 % — 30% 280 278 $ 14,975 $ 5,544

Share Based Compensation (Table

Share Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Share Based Compensation Plans	Share Award Transactions. The following transactions have occurred in connection with the Company’s share based compensation under the 2017 Plan during the year ended December 31, 2017 : Director Stock Awards Granted 3,000 Restricted Stock Activity: Outstanding as of the beginning of year — Granted - 2017 Plan 1,000 Distributed by SEACOR Holdings in connection with the Spin-off 120,693 Vested — Forfeited — Outstanding as of the end of year 121,693 Stock Option Activity: Outstanding as of the beginning of year — Granted - 2017 Plan 613,700 Exercised — Forfeited — Expired — Outstanding as of the end of year 613,700

Commitments And Contingencies S

Commitments And Contingencies Schedule of Operating Lease Payments (Tables)	12 Months Ended
	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Unrecorded Unconditional Purchase Obligations Disclosure [Table Text Block]	The Company’s capital commitments by year of expected payment are as follows (in thousands): 2018 $ 13,435 2019 21,919 2020 10,696 Deferred (estimated based on current construction pricing) 20,697 $ 66,747
Schedule of Future Minimum Rental Payments for Operating Leases [Table Text Block]	Future minimum payments in the years ended December 31 under operating leases that have a remaining term in excess of one year as of December 31, 2017 were as follows (in thousands): 2018 $ 16,525 2019 16,525 2020 13,460 2021 6,143 2022 6

Commitments And Contingencies C

Commitments And Contingencies Capital Committments (Tables) $ in Thousands	Dec. 31, 2017USD ($)
Commitments and Contingencies Disclosure [Abstract]
2,018	$ 13,435
2,019	21,919
2,020	10,696
Deferred	20,697
Unrecorded Unconditional Purchase Obligation	$ 66,747

Major Customers And Segment I40

Major Customers And Segment Information (Tables)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting [Abstract]
Operating Results, Capital Expenditures And Assets By Reporting 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 Brazil, Mexico, Central and South America Europe (primarily North Sea) Total For the year ended December 31, 2017 Operating Revenues: Time charter $ 18,079 $ 32,866 $ 33,410 $ 2,977 $ 73,213 $ 160,545 Bareboat charter — — — 4,636 — 4,636 Other 4,217 1,080 474 552 2,279 8,602 22,296 33,946 33,884 8,165 75,492 173,783 Direct Costs and Expenses: Operating: Personnel 15,621 13,419 16,883 809 34,768 81,500 Repairs and maintenance 3,594 5,957 9,037 274 8,793 27,655 Drydocking 1,828 2,180 968 — 4,059 9,035 Insurance and loss reserves 3,286 677 1,444 316 801 6,524 Fuel, lubes and supplies 1,485 2,815 3,727 223 3,782 12,032 Other 249 3,319 5,240 117 980 9,905 26,063 28,367 37,299 1,739 53,183 146,651 Direct Vessel Profit (Loss) $ (3,767 ) $ 5,579 $ (3,415 ) $ 6,426 $ 22,309 27,132 Other Costs and Expenses: Operating: Leased-in equipment $ 8,152 $ 3,870 $ 862 $ — $ 64 12,948 Administrative and general 56,217 Depreciation and amortization $ 22,060 $ 9,280 $ 17,724 $ 3,608 $ 10,107 62,779 131,944 Losses on Asset Dispositions and Impairments, Net (23,547 ) Operating Loss $ (128,359 ) As of December 31, 2017 Property and Equipment: Historical cost $ 410,475 $ 192,600 $ 326,378 $ 72,484 $ 177,899 $ 1,179,836 Accumulated depreciation (230,636 ) (57,228 ) (100,435 ) (37,281 ) (134,580 ) (560,160 ) $ 179,839 $ 135,372 $ 225,943 $ 35,203 $ 43,319 $ 619,676	United States (primarily Gulf of Mexico) Africa (primarily West Africa) Middle East and Asia Brazil, Mexico, Central and South America Europe (primarily North Sea) Total For the year ended December 31, 2016 Operating Revenues: Time charter $ 28,902 $ 36,706 $ 41,657 $ 196 $ 78,866 $ 186,327 Bareboat charter — — — 8,833 — 8,833 Other 3,954 856 12,230 1,180 2,256 20,476 32,856 37,562 53,887 10,209 81,122 215,636 Direct Costs and Expenses: Operating: Personnel 22,305 12,628 18,381 2,117 39,713 95,144 Repairs and maintenance 2,721 2,628 6,426 232 9,275 21,282 Drydocking 228 1,098 2,117 — 4,378 7,821 Insurance and loss reserves 3,363 539 731 43 1,006 5,682 Fuel, lubes and supplies 1,392 2,512 4,215 21 3,948 12,088 Other 271 2,519 3,247 114 1,180 7,331 30,280 21,924 35,117 2,527 59,500 149,348 Direct Vessel Profit $ 2,576 $ 15,638 $ 18,770 $ 7,682 $ 21,622 66,288 Other Costs and Expenses: Operating: Leased-in equipment $ 7,975 $ 3,898 $ 4,389 $ 913 $ 402 17,577 Administrative and general 49,308 Depreciation and amortization $ 27,052 $ 6,720 $ 11,550 $ 4,083 $ 8,664 58,069 124,954 Losses on Asset Dispositions and Impairments, Net (116,222 ) Operating Loss $ (174,888 ) As of December 31, 2016 Property and Equipment: Historical cost $ 404,226 $ 136,428 $ 197,389 $ 57,744 $ 162,972 $ 958,759 Accumulated depreciation (233,075 ) (60,794 ) (97,433 ) (34,455 ) (114,862 ) (540,619 ) $ 171,151 $ 75,634 $ 99,956 $ 23,289 $ 48,110 $ 418,140	United States (primarily Gulf of Mexico) Africa (primarily West Africa) Middle East and Asia Brazil, Mexico, Central and South America Europe (primarily North Sea) Total For the year ended December 31, 2015 Operating Revenues: Time charter $ 111,892 $ 53,724 $ 48,541 $ 17,585 $ 99,148 $ 330,890 Bareboat charter — — — 8,598 — 8,598 Other 6,859 3,528 14,951 1,602 2,440 29,380 118,751 57,252 63,492 27,785 101,588 368,868 Direct Costs and Expenses: Operating: Personnel 52,843 15,677 20,614 7,406 54,066 150,606 Repairs and maintenance 8,697 4,692 8,678 1,237 13,067 36,371 Drydocking 6,430 757 1,275 1,859 7,460 17,781 Insurance and loss reserves 5,193 1,165 1,448 535 1,557 9,898 Fuel, lubes and supplies 6,785 2,705 5,033 673 5,566 20,762 Other 4,456 4,085 7,316 849 1,339 18,045 84,404 29,081 44,364 12,559 83,055 253,463 Direct Vessel Profit $ 34,347 $ 28,171 $ 19,128 $ 15,226 $ 18,533 115,405 Other Costs and Expenses: Operating: Leased-in equipment $ 10,891 $ 4,695 $ 4,364 $ 2,545 $ 14 22,509 Administrative and general 53,085 Depreciation and amortization $ 26,605 $ 8,580 $ 11,209 $ 5,623 $ 9,712 61,729 137,323 Losses on Asset Dispositions and Impairments, Net (17,017 ) Operating Loss $ (38,935 ) As of December 31, 2015 Property and Equipment: Historical cost $ 447,862 $ 144,880 $ 218,927 $ 87,612 $ 203,338 $ 1,102,619 Accumulated depreciation (198,556 ) (71,965 ) (88,722 ) (48,303 ) (139,416 ) (546,962 ) $ 249,306 $ 72,915 $ 130,205 $ 39,309 $ 63,922 $ 555,657
Summarized Financial Information For The Company's Investments, At Equity	Investments, at equity, and advances to 50% or less owned companies as of December 31 were as follows (in thousands): Ownership 2017 2016 MexMar 49.0% $ 60,980 $ 63,404 OSV Partners 30.4% 10,006 9,245 Nautical Power 50.0% 6,408 6,413 Dynamic Offshore Drilling 19.0% 4,958 15,871 Falcon Global 50.0% — 18,539 Sea Cat Crewzer II 50.0% — 11,246 Sea-Cat Crewzer 50.0% — 4,088 Other 20.0% — 50.0% 9,817 9,505 $ 92,169 $ 138,311 Equity in earnings (losses) of 50% or less owned companies, net of tax for the years ended December 31 were as follows (in thousands): 2017 2016 2015 MexMar $ 10,103 $ 3,556 $ 5,650 Other (6,026 ) (9,870 ) 3,107 $ 4,077 $ (6,314 ) $ 8,757

Supplemental Information For 41

Supplemental Information For Statements Of Cash Flows (Tables)	12 Months Ended
	Dec. 31, 2017
Supplemental Cash Flow Information [Abstract]
Cash Flow Supplemental Information	Supplemental information for the years ended December 31 was as follows (in thousands): 2017 2016 2015 Income taxes refunded, net $ 33,773 $ 10,224 $ 1,667 Interest paid, excluding capitalized interest 9,216 2,698 22,407 Schedule of Non-Cash Investing and Financing Activities: Exchange of receivable for investment in 50% or less owned company 1,000 — — Services received to settle notes receivable — — 2,500 Equipment received to settle notes receivable — 11,900 — Financial support from SEACOR Holdings upon issuance of the Company’s convertible senior notes — — 8,511

Quarterly Financial Informati42

Quarterly Financial Information (Tables)	12 Months Ended
	Dec. 31, 2017
Quarterly Financial Data [Abstract]
Quarterly Financial Information	Three Months Ended Dec. 31, Sept. 30, June 30, March 31, 2017 Operating Revenues $ 49,343 $ 47,813 $ 42,323 $ 34,304 Operating Loss (35,830 ) (29,129 ) (44,815 ) (18,585 ) Net Income (Loss) 27,904 (22,356 ) (36,489 ) (7,599 ) Net Income (Loss) attributable to SEACOR Marine Holdings Inc. 28,961 (20,475 ) (33,992 ) (7,395 ) Basic Income (Loss) Per Common Share of SEACOR Marine Holdings Inc. $ 1.65 $ (1.17 ) $ (1.93 ) $ (0.42 ) Diluted Income (Loss) Per Common Share of SEACOR Marine Holdings Inc. $ 1.20 $ (1.25 ) $ (1.93 ) $ (0.42 ) 2016 Operating Revenues $ 44,361 $ 54,125 $ 57,271 $ 59,879 Operating Loss (82,719 ) (41,068 ) (34,514 ) (16,587 ) Net Loss (61,774 ) (28,007 ) (30,789 ) (12,580 ) Net Loss attributable to SEACOR Marine Holdings Inc. (61,575 ) (27,933 ) (30,580 ) (11,959 ) Basic and Diluted Loss Per Common Share of SEACOR Marine Holdings Inc. $ (3.48 ) $ (1.58 ) $ (1.73 ) $ (0.68 )

Nature Of Operations And Acco43

Nature Of Operations And Accounting Policies (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Sep. 30, 2017
Nature of Operations and Accounting Policies [Line Items]
Depreciation		$ 62.8	$ 58	$ 60.8
Capitalized interest		3.6	7	4.4
Amortization expense			0.1	0.9
Equity Method Investment, Other than Temporary Impairment		$ 8.8	6.9
Goodwill, Impairment Loss				13.4
Debt Instrument, Interest Rate, Stated Percentage		3.75%
Offshore Support Vessels [Member]
Nature of Operations and Accounting Policies [Line Items]
Asset Impairment Charges		$ (27.5)	$ (119.7)	$ (7.1)
Three Point Seven Five Percentage Convertible Notes [Member]
Nature of Operations and Accounting Policies [Line Items]
Debt Instrument, Interest Rate, Stated Percentage		3.75%			3.75%
Convertible Debt Securities [Member] | Three Point Seven Five Percentage Convertible Notes [Member]
Nature of Operations and Accounting Policies [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount		4,070,500
Employee Stock Option [Member] | Stock Compensation Plan [Member]
Nature of Operations and Accounting Policies [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount		613,700
Restricted Stock [Member] | Stock Compensation Plan [Member]
Nature of Operations and Accounting Policies [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount		121,693
Subsequent Event [Member]
Nature of Operations and Accounting Policies [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification	$ 12.1

Nature Of Operations And Acco44

Nature Of Operations And Accounting Policies (Deferred Revenues Included In Other Current Liabilities) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Balance at beginning of period	$ 6,953	$ 6,953	$ 6,794
Revenues deferred during the year	4,699	0	159
Deferred Revenue, Revenue Recognized	(1,548)	0	0
Balance at end of period	10,104	$ 6,953	$ 6,953
Domestic Destination [Member]
Balance at end of period	6,800
Geographic Distribution, Foreign [Member]
Balance at end of period	$ 3,200

Nature Of Operations And Acco45

Nature Of Operations And Accounting Policies (Estimated Useful life Of Major Assets) (Details)	12 Months Ended
	Dec. 31, 2017
Offshore Support Vessels [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	20 years
Wind Farm Utility Vessel [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	10 years

Nature Of Operations And Acco46

Nature Of Operations And Accounting Policies (Schedule Of Property And Equipment By Major Classes) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 1,179,836	$ 958,759	$ 1,102,619
Accumulated Depreciation	(560,160)	(540,619)
Property, Plant and Equipment, Other, Gross	619,676	418,140
Offshore Support Vessels Anchor Handling Towing Supply [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	198,222	228,857
Accumulated Depreciation	(174,159)	(183,757)
Property, Plant and Equipment, Other, Gross	24,063	45,100
Offshore Support Vessels Fast Support [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	424,865	251,415
Accumulated Depreciation	(89,980)	(72,599)
Property, Plant and Equipment, Other, Gross	334,885	178,816
Offshore Support Vessels Supply [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	105,360	96,774
Accumulated Depreciation	(51,494)	(58,028)
Property, Plant and Equipment, Other, Gross	53,866	38,746
Offshore Support Vessels Standby Safety [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	118,414	109,436
Accumulated Depreciation	(97,603)	(88,020)
Property, Plant and Equipment, Other, Gross	20,811	21,416
Offshore Support Vessels Specialty [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	30,529	45,765
Accumulated Depreciation	(19,304)	(24,063)
Property, Plant and Equipment, Other, Gross	11,225	21,702
Liftboats [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	196,504	104,356
Accumulated Depreciation	(54,161)	(45,447)
Property, Plant and Equipment, Other, Gross	142,343	58,909
Wind Farm Utility Vessel [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	65,976	60,671
Accumulated Depreciation	(40,358)	(29,019)
Property, Plant and Equipment, Other, Gross	25,618	31,652
Offshore Support Vessels Machinery and Spares [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	14,385	32,921
Accumulated Depreciation	(13,244)	(20,008)
Property, Plant and Equipment, Other, Gross	1,141	12,913
Property, Plant and Equipment, Other Types [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	25,581	28,564
Accumulated Depreciation	(19,857)	(19,678)
Property, Plant and Equipment, Other, Gross	$ 5,724	$ 8,886

Nature Of Operations And Acco47

Nature Of Operations And Accounting Policies (Schedule Of Deferred Gain Activity) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Sale Leaseback and Financed Equipment Sales
Deferred Revenue Arrangement [Line Items]
Balance at beginning of period	$ 32,035	$ 40,234	$ 50,934
Amortization of deferred gains included in operating expenses as a reduction to rental expense	(8,118)	(8,199)	(8,199)
Amortization Of Deferred Gains Included In Gains On Asset Dispositions And Impairments, Net	0	0	2,501
Other	(364)	0	0
Balance at end of period	23,553	32,035	40,234
Fifty Percent Or Less Owned Subsidiaries
Deferred Revenue Arrangement [Line Items]
Balance at beginning of period	1,875	3,064	3,136
Amortization Of Deferred Gains Included In Gains On Asset Dispositions And Impairments, Net	0	36	72
Other	(422)	(1,153)	0
Balance at end of period	$ 1,453	$ 1,875	$ 3,064

Nature Of Operations And Acco48

Nature Of Operations And Accounting Policies Nature Of Operations And Accounting Policies (Schedule of Accumulated Other Comprehensive Income (Loss))(Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Amount	$ 43,700
Accumulated Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Net of Tax	(13,195)	$ (11,413)	$ (5,985)	$ (3,664)
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, before Tax, Portion Attributable to Parent	4,397	(8,351)	(3,571)
Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Tax, Portion Attributable to Parent	(6,179)	2,923	1,250
Accumulated Other Comprehensive Income (Loss), Cumulative Changes in Net Gain (Loss) from Cash Flow Hedges, Effect Net of Tax	702	76	(110)	19
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, before Tax, Portion Attributable to Parent	703	286	(198)
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Tax, Portion Attributable to Parent	(77)	(100)	69
Accumulated Other Comprehensive Income (Loss), Net of Tax	(12,493)	(11,337)	(6,095)	(3,645)
Other Comprehensive Income (Loss), before Tax, Portion Attributable to Parent	5,100	(8,065)	(3,769)
Other Comprehensive Income (Loss), Tax, Portion Attributable to Parent	(6,256)	2,823	1,319
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, before Tax, Portion Attributable to Noncontrolling Interest	257	(1,085)	(442)
Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Tax, Portion Attributable to Noncontrolling Interest	0	0	0
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax, Portion Attributable to Noncontrolling Interest	18	(17)	0
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Tax, Portion Attributable to Noncontrolling Interest	0	0	0
Other Comprehensive Loss, before Tax	5,375	(9,167)	(4,211)
Other Comprehensive Income (Loss), Tax	(6,256)	2,823	1,319
Other Comprehensive Income (Loss), Net of Tax	(881)	(6,344)	(2,892)
Non-Controlling Interests In Subsidiaries [Member]
Accumulated Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Net of Tax	(1,357)	(1,614)	(529)	(87)
Accumulated Other Comprehensive Income (Loss), Cumulative Changes in Net Gain (Loss) from Cash Flow Hedges, Effect Net of Tax	1	(17)	0	$ 0
Other Comprehensive Income (Loss), Net of Tax	275	$ (1,102)	$ (442)
Deferred Income Tax Charge [Member]
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Amount	$ 4,500

Business Acquisitions (Details)

Business Acquisitions (Details)	9 Months Ended	12 Months Ended
	Sep. 30, 2017USD ($)equipment	Dec. 31, 2017USD ($)equipment	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Apr. 28, 2017	Dec. 12, 2016USD ($)
Business Acquisition [Line Items]
Restricted cash	$ 235,000	$ 0	$ 275,000
Trade and other receivables	4,148,000		1,250,000
Other current assets	(15,700,000)		0
Investments, at Equity, and Advances to 50% or Less Owned Companies	(61,626,000)		0
Property and Equipment			1,367,000
Accounts payable	(747,000)		199,000
Other current liabilities	76,000		0
Long-Term Debt	41,186,000		(3,091,000)
Other Liabilities	$ 43,000		0
Purchase price		9,751,000	0
Cash Acquired from Acquisition		$ (1,943,000)	0	$ 0
Sea Cat Crewzer [Member]
Business Acquisition [Line Items]
Equity Method Investment, Ownership Percentage		50.00%			100.00%
Number of Equipment Operated | equipment	2
Business Acquisition, Percentage of Voting Interests Acquired					50.00%
Payments to Acquire Businesses, Gross	$ 4,400,000	$ 4,400,000
Cash Acquired from Acquisition		$ (5,900,000)
Sea-Cat Crewzer II [Member]
Business Acquisition [Line Items]
Equity Method Investment, Ownership Percentage		50.00%			100.00%
Number of Equipment Operated | equipment	2	2
Business Acquisition, Percentage of Voting Interests Acquired					50.00%
Payments to Acquire Businesses, Gross	$ 11,300,000	$ 11,300,000
Cypress CKOR LLC [Member]
Business Acquisition [Line Items]
Business Acquisition, Percentage of Voting Interests Acquired						100.00%
Payments to Acquire Businesses, Gross			$ 1
Long-Term Debt						$ 3,100,000

Equipment Acquisitions And Di50

Equipment Acquisitions And Dispositions (Major Equipment Deliveries) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)equipment	Dec. 31, 2016USD ($)equipment	Dec. 31, 2015USD ($)equipment
Number Of Equipments Acquired	11	17	6
Payments to Acquire Property, Plant, and Equipment | $	$ 69,021	$ 100,884	$ 87,765
Offshore Support Vessels Fast Support [Member]
Number Of Equipments Acquired	6	12	3
Offshore Support Vessels Supply [Member]
Number Of Equipments Acquired	5	2	1
Offshore Support Vessels Specialty [Member]
Number Of Equipments Acquired	0	1	0
Wind Farm Utility Vessel [Member]
Number Of Equipments Acquired	0	2	2
Sea Cat Crewzer [Member] | Offshore Support Vessels Fast Support [Member]
Number Of Equipments Acquired	4
Falcon Global [Member] | Liftboats [Member]
Number Of Equipments Acquired	2
Fair Value Hedging [Member]
Payments to Acquire Property, Plant, and Equipment | $	$ 69,400	$ 101,300	$ 87,800

Equipment Acquisitions And Di51

Equipment Acquisitions And Dispositions (Narrative) (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Business Acquisition [Line Items]
Sales Price Of Equipment		$ 11,200	$ 41,400	$ 15,700
Proceeds from Sale of Property, Plant, and Equipment		10,843	41,919	15,698
Deposits		100	500
Disposal Group, Disposed of by Sale, Not Discontinued Operations [Member]
Business Acquisition [Line Items]
Proceeds from Sale of Property, Plant, and Equipment		10,700
Gain (Loss) on Asset Dispositions and Impairments, Net [Member]
Business Acquisition [Line Items]
Gain (Loss) on Disposition of Property Plant Equipment		$ 3,900	$ 3,500	900
Amortization of Deferred Charges				$ 2,600
Other Current Liabilities [Member] | Disposal Group, Disposed of by Sale, Not Discontinued Operations [Member]
Business Acquisition [Line Items]
Proceeds from Sale of Property, Plant, and Equipment	$ 500

Equipment Acquisitions And Di52

Equipment Acquisitions And Dispositions (Major Equipment Dispositions) (Details) - equipment	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Number of Equipments Removed from Service	4	9	2
Offshore Support Vessels Fast Support [Member]
Number of Equipments Removed from Service	0	0	1
Offshore Support Vessels Standby Safety [Member]
Number of Equipments Removed from Service	1	4	0
Offshore Support Vessels Supply [Member]
Number of Equipments Removed from Service	1	5	1
Liftboats [Member]
Number of Equipments Removed from Service	2	0	0
Disposal Group, Disposed of by Sale, Not Discontinued Operations [Member]
Number of Equipments Removed from Service	9

Investments, At Equity, And A53

Investments, At Equity, And Advances To 50% Or Less Owned Companies (Investments, At Equity, And Advances To 50% Or Less Owned Companies) (Details) - USD ($) $ in Thousands	Jan. 17, 2018	Dec. 31, 2017	Apr. 28, 2017	Dec. 31, 2016
Schedule of Equity Method Investments [Line Items]
Equity Method Investments		$ 92,169		$ 138,311
MexMar [Member]
Schedule of Equity Method Investments [Line Items]
Ownership of equity interest		49.00%
Equity Method Investments		$ 60,980		63,404
OSV Partners [Member]
Schedule of Equity Method Investments [Line Items]
Ownership of equity interest		30.40%
Equity Method Investments		$ 10,006		9,245
Nautical Power [Member]
Schedule of Equity Method Investments [Line Items]
Ownership of equity interest		50.00%
Equity Method Investments		$ 6,408		6,413
Dynamic Offshore Drilling Ltd. [Member]
Schedule of Equity Method Investments [Line Items]
Ownership of equity interest		19.00%
Equity Method Investments		$ 4,958		15,871
Falcon Global [Member]
Schedule of Equity Method Investments [Line Items]
Ownership of equity interest		50.00%
Equity Method Investments		$ 0		18,539
Sea-Cat Crewzer II [Member]
Schedule of Equity Method Investments [Line Items]
Ownership of equity interest		50.00%	100.00%
Equity Method Investments		$ 0		11,246
Sea Cat Crewzer [Member]
Schedule of Equity Method Investments [Line Items]
Ownership of equity interest		50.00%	100.00%
Equity Method Investments		$ 0		4,088
Other [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investments		$ 9,817		$ 9,505
Other [Member] | Minimum [Member]
Schedule of Equity Method Investments [Line Items]
Ownership of equity interest		20.00%
Other [Member] | Maximum [Member]
Schedule of Equity Method Investments [Line Items]
Ownership of equity interest		50.00%
Subsequent Event [Member] | SEACOSCO Offshore LLC [Member]
Schedule of Equity Method Investments [Line Items]
Ownership of equity interest	50.00%

Investments, At Equity, And A54

Investments, At Equity, And Advances To 50% Or Less Owned Companies (Summarized Financial Information For The Company's Investments, At Equity) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
MexMar [Member]
Current assets	$ 71,990	$ 50,996
Noncurrent assets	194,990	209,806
Current liabilities	23,931	23,089
Noncurrent liabilities	147,043	151,515
Operating Revenues	67,003	70,521	$ 78,363
Costs and Expenses: Operating and administrative	29,405	37,613	41,837
Costs and Expenses: Depreciation	15,977	13,958	13,089
Total costs and expenses	45,382	51,571	54,926
Operating Income	21,621	18,950	23,437
Net Income (Loss)	9,233	6,476	15,638
Other [Member]
Current assets	61,360	78,071
Noncurrent assets	247,038	255,270
Current liabilities	14,603	32,731
Noncurrent liabilities	138,789	158,628
Operating Revenues	77,409	77,571	92,559
Costs and Expenses: Operating and administrative	46,748	51,136	57,922
Costs and Expenses: Depreciation	12,198	13,181	13,961
Total costs and expenses	58,946	64,317	71,883
Gain (Loss) on Asset Dispositions	0	(21,323)	(2,201)
Operating Income	18,463	(8,069)	18,475
Net Income (Loss)	6,451	(19,229)	3,829
Falcon Global, Sea-Cat Crewzer and Sea-Cat Crewzer II [Member]
Current assets		14,834
Noncurrent assets		166,076
Current liabilities		9,624
Noncurrent liabilities		90,693
Operating Revenues	5,075	21,611	24,439
Costs and Expenses: Operating and administrative	3,752	12,837	9,441
Costs and Expenses: Depreciation	2,324	3,694	3,708
Total costs and expenses	6,076	16,531	13,149
Operating Income	(1,001)	5,080	11,290
Net Income (Loss)	$ (2,699)	$ 778	$ 6,468

Investments, At Equity, And A55

Investments, At Equity, And Advances To 50% Or Less Owned Companies (Narrative) (Details) $ in Thousands	3 Months Ended	9 Months Ended	12 Months Ended
	Mar. 31, 2017USD ($)equipment	Sep. 30, 2017USD ($)equipment	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)equipment	Dec. 31, 2016USD ($)equipment	Dec. 31, 2015USD ($)equipment	Jan. 17, 2018USD ($)	Apr. 28, 2017
Cumulative undistributed net earnings of 50% or less owned companies accounted for by the equity method included in the Company's consolidated retained earnings				$ 46,100	$ 38,700
Number Of Equipments Acquired | equipment				11	17	6
Equity Method Investment, Other than Temporary Impairment				$ 8,800	$ 6,900
Trade and other receivables		$ 4,148			1,250
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Assets		61,626			0
Property and Equipment					1,367
Accounts payable		(747)			199
Other current liabilities		76			0
Long-Term Debt		41,186			(3,091)
Other Liabilities		$ 43			0
Noncontrolling interests in subsidiaries				14,975	5,544
Payments to Acquire Property, Plant, and Equipment				69,021	100,884	$ 87,765
Unrecorded Unconditional Purchase Obligation, Due in Next Twelve Months				13,435
Unrecorded Unconditional Purchase Obligation				66,747
Offshore Support Vessels [Member]
Asset Impairment Charges				$ 27,500	$ 119,700	$ 7,100
Offshore Support Vessels Fast Support [Member]
Number Of Equipments Acquired | equipment				6	12	3
Other [Member]
Operating Revenues				$ 77,409	$ 77,571	$ 92,559
Costs and Expenses: Operating and administrative				46,748	51,136	57,922
Costs and Expenses: Depreciation				12,198	13,181	13,961
Equity Method Investment Summarized Financial Information Total Costs and Expenses				58,946	64,317	71,883
Operating Income				18,463	(8,069)	18,475
Net Income (Loss)				6,451	(19,229)	3,829
MexMar [Member]
Operating Revenues				67,003	70,521	78,363
Partners' Capital Account, Contributions					$ 7,400	7,900
Number Of Equipments Acquired | equipment					2
Repayments of Secured Debt						15,000
Payments to Acquire Machinery and Equipment					$ 34,000
Related Party Transaction, Revenues from Transactions with Related Party				$ 300	300	400
Related party transaction expense					5,100	11,600
Equity Method Investment, Ownership Percentage				49.00%
Proceeds from Equity Method Investment, Dividends or Distributions, Return of Capital				$ 7,400
Costs and Expenses: Operating and administrative				29,405	37,613	41,837
Costs and Expenses: Depreciation				15,977	13,958	13,089
Equity Method Investment Summarized Financial Information Total Costs and Expenses				45,382	51,571	54,926
Operating Income				21,621	18,950	23,437
Net Income (Loss)				$ 9,233	6,476	15,638
MexMar [Member] | Offshore Support Vessels [Member]
Number of Equipment Operated | equipment				15
Falcon Global [Member]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Cash and Equivalents	$ 1,943
Partners' Capital Account, Contributions	400
Equity Method Investment, Ownership Percentage				50.00%
Payments for Advance to Affiliate	$ 2,000
Business Acquisition, Percentage of Voting Interests Acquired	100.00%
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Marketable Securities	$ 785
Trade and other receivables	291
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Assets	19,374
Property and Equipment	96,000
Accounts payable	3,201
Other current liabilities	1,153
Long-Term Debt	58,335
Other Liabilities	1,000
Noncontrolling interests in subsidiaries	$ 17,374
Falcon Global [Member] | Liftboats [Member]
Number of Equipment Operated | equipment	2
Sea-Cat Crewzer II [Member]
Number of Equipment Operated | equipment		2		2
Equity Method Investment, Ownership Percentage				50.00%				100.00%
Business Acquisition, Percentage of Voting Interests Acquired								50.00%
Payments to Acquire Businesses, Gross		$ 11,300		$ 11,300
OSV Partners [Member]
Partners' Capital Account, Contributions				2,300	1,200	1,400
Related Party Transaction, Revenues from Transactions with Related Party				600	500	1,200
Secured Long-term Debt, Noncurrent				$ 29,300
Equity Method Investment, Ownership Percentage				30.40%
OSV Partners [Member] | Offshore Support Vessels [Member]
Asset Impairment Charges					1,000
Dynamic Offshore Drilling Ltd. [Member]
Equity Method Investment, Other than Temporary Impairment				$ 8,300
Equity Method Investment, Ownership Percentage				19.00%
Nautical Power [Member]
Equity Method Investment, Ownership Percentage				50.00%
Sea Cat Crewzer [Member]
Number of Equipment Operated | equipment		2
Equity Method Investment, Ownership Percentage				50.00%				100.00%
Business Acquisition, Percentage of Voting Interests Acquired								50.00%
Payments to Acquire Businesses, Gross		$ 4,400		$ 4,400
Other Offshore Marine Services Joint Ventures [Member]
Partners' Capital Account, Contributions				800	500
Repayments of Advances				(200)		(200)
Related Party Transaction, Revenues from Transactions with Related Party				700	800	800
Equity Method Investment, Other than Temporary Impairment				500	500
Proceeds from Equity Method Investment, Dividends or Distributions, Return of Capital				2,600	800	900
Allocable share of uncalled capital				1,400
Guarantee of outstanding charter receivables				$ 400
Other Offshore Marine Services Joint Ventures [Member] | Offshore Support Vessels [Member]
Number of Equipment Operated | equipment				9
Other Offshore Marine Services Joint Ventures [Member] | Offshore Support Vessels [Member]
Asset Impairment Charges					$ 2,700	$ 2,000
General Partner [Member] | OSV Partners [Member]
Partners' Capital Account, Contributions				$ 6,000
Equity Method Investment, Ownership Percentage				38.60%
Subsequent Event [Member]
Unrecorded Unconditional Purchase Obligation, Due in Next Twelve Months			$ 10,100
Unrecorded Unconditional Purchase Obligation			11,000
Subsequent Event [Member] | SEACOSCO Offshore LLC [Member]
Equity Method Investment, Ownership Percentage							50.00%
Payments to Acquire Property, Plant, and Equipment			$ 161,100
Unrecorded Unconditional Purchase Obligation, Due in Next Twelve Months							$ 20,000
Unrecorded Unconditional Purchase Obligation							$ 27,500

Construction Reserve Funds (Det

Construction Reserve Funds (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Other Restricted Assets [Abstract]
Withdrawals	$ (39,163)	$ (87,820)	$ (24,871)
Deposits	6,315	27,414	18,054
Construction Reserve Fund Activity Net	$ (32,848)	$ (60,406)	$ (6,817)

Third Party Notes Receivable (D

Third Party Notes Receivable (Details) $ in Millions	12 Months Ended
	Dec. 31, 2015USD ($)
Notes, Loans and Financing Receivable, Net, Noncurrent [Abstract]
Notes receivable third party	$ (13.6)

Long-Term Debt (Schedule Of Com

Long-Term Debt (Schedule Of Company's Borrowings) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 12, 2016	Dec. 01, 2015
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 348,059	$ 249,041
Portion due within one year, net of related debt discount and issuance costs	(22,858)	(20,400)
Debt discount included in long-term debt	(27,373)	(4,567)
Debt issuance costs included in long-term debt	(5,787)	(6,269)
Long-term Debt, Excluding Current Maturities	292,041	217,805
Three Point Seven Five Percentage Convertible Notes [Member]
Debt Instrument [Line Items]
Convertible Debt	175,000	175,000		$ 175,000
Debt discount included in long-term debt				$ (8,500)
Falcon Global [Member]
Debt Instrument [Line Items]
Secured Long-term Debt, Noncurrent	54,870	0
Sea-Cat Crewzer III [Member]
Debt Instrument [Line Items]
Secured Long-term Debt, Noncurrent	29,078	22,785
Windcat Workboats Ltd. [Member]
Debt Instrument [Line Items]
Secured Long-term Debt, Noncurrent	25,202	22,118
Sea-Cat Crewzer II [Member]
Debt Instrument [Line Items]
Secured Long-term Debt, Noncurrent	20,871	0
Sea Cat Crewzer [Member]
Debt Instrument [Line Items]
Secured Long-term Debt, Noncurrent	18,504	0
C-Lift [Member]
Debt Instrument [Line Items]
Secured Long-term Debt, Noncurrent	16,000	17,500
BNDES [Member]
Debt Instrument [Line Items]
Secured Long-term Debt, Noncurrent	7,234	9,186
Cypress CKOR LLC [Member]
Debt Instrument [Line Items]
Secured Long-term Debt, Noncurrent	$ 1,300	$ 2,452	$ 3,100

Long-Term Debt (Schedule Of Lon

Long-Term Debt (Schedule Of Long-Term Debt Maturities) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Long-term Debt, Unclassified [Abstract]
2,018	$ 22,858
2,019	54,533
2,020	10,358
2,021	34,989
2,022	208,618
Years subsequent to 2022	16,703
Long-term Debt, Gross	$ 348,059	$ 249,041

Long-Term Debt (Narrative) (Sen

Long-Term Debt (Narrative) (Senior Notes And Convertible Debentures) (Details) $ / shares in Units, € in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2016USD ($)	Dec. 31, 2017USD ($)$ / sharesshares	Dec. 31, 2016USD ($)$ / shares	Dec. 31, 2016EUR (€)	Dec. 31, 2015USD ($)	Sep. 30, 2017USD ($)	Apr. 28, 2017	Mar. 31, 2017USD ($)	Dec. 12, 2016USD ($)	May 24, 2016EUR (€)	Apr. 21, 2016EUR (€)	Dec. 01, 2015USD ($)	Aug. 03, 2015USD ($)	Jun. 06, 2013
Debt Instrument [Line Items]
Debt instrument, stated percentage		3.75%
Debt Instrument, Unamortized Discount		$ 27,373,000	$ 4,567,000
Common Stock, Par or Stated Value Per Share | $ / shares		$ 0.01	$ 0.01
Letters of credit outstanding amount		$ 2,800,000
Long-Term Debt			$ (3,091,000)			$ 41,186,000
Three Point Seven Five Percentage Convertible Notes [Member]
Debt Instrument [Line Items]
Debt instrument, stated percentage		3.75%				3.75%
Convertible Debt		$ 175,000,000	175,000,000									$ 175,000,000
Debt Instrument, Unamortized Discount												8,500,000
Debt Issuance Costs, Gross												$ 6,400,000
Common Stock, Par or Stated Value Per Share | $ / shares		$ 0.01
Individual Bond, Face Value		$ 1,000
Debt Instrument, Convertible, Conversion Ratio		23.26
Convertible Securities | shares		4,070,500
Bond Redemption Percentage		100.00%
Debt Instrument, Interest Rate, Effective Percentage		7.95%										8.70%
Embedded Derivative, Fair Value of Embedded Derivative Liability												$ 27,300,000
Falcon Global [Member]
Debt Instrument [Line Items]
Payments of Debt Issuance Costs		$ 200,000
Debt Instrument, Interest Rate, Effective Percentage		5.25%
Secured Long-term Debt, Noncurrent		$ 54,870,000	0
Sea-Cat Crewzer III [Member]
Debt Instrument [Line Items]
Debt Issuance Costs, Gross			2,700,000
Aggregate principal amount | €											€ 27.6
Proceeds from issuance of long-term debt, net of offering costs		$ 7,100,000	22,800,000
Debt Instrument, Interest Rate, Effective Percentage		2.76%
Repayments of Long-term Debt		$ (600,000)
Secured Long-term Debt, Noncurrent		29,078,000	22,785,000
Windcat Workboats Ltd. [Member]
Debt Instrument [Line Items]
Debt Issuance Costs, Gross			600,000
Line of Credit Facility, Maximum Borrowing Capacity | €										€ 25
Proceeds from Lines of Credit			23,500,000	€ 21
Repayments of Long-term Debt			(22,900,000)		$ (3,200,000)
Secured Long-term Debt, Noncurrent		$ 25,202,000	$ 22,118,000
Windcat Workboats Ltd. [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate			3.00%	3.00%
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage			1.20%	1.20%
Windcat Workboats Ltd. [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate			3.30%	3.30%
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage			1.32%	1.32%
Sea-Cat Crewzer II [Member]
Debt Instrument [Line Items]
Debt instrument, stated percentage		1.52%
Payments of Debt Issuance Costs		$ 100,000
Debt Instrument, Final Baloon Payment		$ 17,300,000
Debt Instrument, Interest Rate, Effective Percentage		5.64%
Repayments of Long-term Debt		$ (1,200,000)
Secured Long-term Debt, Noncurrent		$ 20,871,000	$ 0
Sea-Cat Crewzer II [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate		2.10%
Sea-Cat Crewzer II [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate		2.75%
Sea Cat Crewzer [Member]
Debt Instrument [Line Items]
Debt instrument, stated percentage		1.52%
Payments of Debt Issuance Costs		$ 100,000
Debt Instrument, Final Baloon Payment		$ 15,300,000
Debt Instrument, Interest Rate, Effective Percentage		5.64%
Repayments of Long-term Debt		$ (1,100,000)
Secured Long-term Debt, Noncurrent		$ 18,504,000	0
Sea Cat Crewzer [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate		2.10%
Sea Cat Crewzer [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate		2.75%
C-Lift [Member]
Debt Instrument [Line Items]
Payments of Debt Issuance Costs		$ 100,000
Debt Instrument, Interest Rate, Effective Percentage		6.19%
Repayments of Long-term Debt		$ (1,500,000)	(1,700,000)		(1,600,000)
Secured Long-term Debt, Noncurrent		$ 16,000,000	17,500,000
BNDES [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Effective Percentage		4.00%
Repayments of Long-term Debt		$ (2,000,000)	(2,000,000)		$ (2,000,000)
Secured Long-term Debt, Noncurrent		7,234,000	9,186,000
Cypress CKOR LLC [Member]
Debt Instrument [Line Items]
Repayments of Long-term Debt		(1,200,000)	(600,000)
Secured Long-term Debt, Noncurrent		$ 1,300,000	$ 2,452,000						$ 3,100,000
Cypress CKOR LLC [Member]
Debt Instrument [Line Items]
Payments to Acquire Businesses, Gross	$ 1
Falcon Global [Member]
Debt Instrument [Line Items]
Debt Issuance Costs, Gross								$ 1,000,000
Equity Method Investment, Ownership Percentage		50.00%
Business Acquisition, Percentage of Voting Interests Acquired								100.00%
Long-Term Debt								$ 58,335,000
Falcon Global [Member] | Tranche A [Member]
Debt Instrument [Line Items]
Aggregate principal amount													$ 62,500,000
Repayments of Long-term Debt		$ (4,400,000)
Falcon Global [Member] | Tranche B [Member]
Debt Instrument [Line Items]
Aggregate principal amount													$ 18,000,000
Cypress CKOR LLC [Member]
Debt Instrument [Line Items]
Equity Method Investment, Ownership Percentage									100.00%
C-Lift [Member]
Debt Instrument [Line Items]
Business Acquisition, Percentage of Voting Interests Acquired														50.00%
Sea Cat Crewzer [Member]
Debt Instrument [Line Items]
Equity Method Investment, Ownership Percentage							100.00%
Business Acquisition, Percentage of Voting Interests Acquired							50.00%
Sea-Cat Crewzer II [Member]
Debt Instrument [Line Items]
Equity Method Investment, Ownership Percentage							100.00%
Business Acquisition, Percentage of Voting Interests Acquired							50.00%

Income Taxes (Narrative) (Detai

Income Taxes (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cumulative undistributed net earnings of foreign subsidiaries included in retained earnings		$ 38.5
Statutory rate		35.00%	35.00%	35.00%
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Amount		$ 43.7
Effective Income Tax Rate Reconciliation, Percent		63.60%	33.40%	32.30%
Subsequent Event [Member]
Statutory rate	(21.00%)
United States [Member]
Operating Loss Carryforwards, Valuation Allowance		$ 3.9
State and Local Jurisdiction [Member]
Operating Loss Carryforwards, Valuation Allowance		$ 0.6

Income Taxes (Schedule Of Incom

Income Taxes (Schedule Of Income Before Income Tax Expense (Benefit) And Equity In Earnings Of 50% Or Less Owned Companies) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Contingency [Line Items]
Income Before Income Tax Expense (Benefit) and Equity in Earnings of 50% or Less Owned Companies	$ (117,023)	$ (190,305)	$ (52,576)
United States [Member]
Income Tax Contingency [Line Items]
Income Before Income Tax Expense (Benefit) and Equity in Earnings of 50% or Less Owned Companies	(90,696)	(169,523)	(47,184)
Foreign [Member]
Income Tax Contingency [Line Items]
Income Before Income Tax Expense (Benefit) and Equity in Earnings of 50% or Less Owned Companies	(45,112)	(28,095)	(1,963)
Eliminations And Other [Member]
Income Tax Contingency [Line Items]
Income Before Income Tax Expense (Benefit) and Equity in Earnings of 50% or Less Owned Companies	$ 18,785	$ 7,313	$ (3,429)

Income Taxes (Components Of Inc

Income Taxes (Components Of Income Tax Expense (Benefit)) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Components of Income Tax Expense (Benefit), Continuing Operations [Abstract]
Federal	$ (16,705)	$ (20,718)	$ (6,814)
State	(42)	(139)	420
Foreign	3,347	5,436	5,907
Current Income Tax Expense, Total	(13,400)	(15,421)	(487)
Federal	(60,750)	(47,692)	(15,956)
State	(172)	(446)	(14)
Foreign	(84)	90	(516)
Deferred Income Tax Benefit, Total	(61,006)	(48,048)	(16,486)
Income Tax Benefit	$ (74,406)	$ (63,469)	$ (16,973)

Income Taxes (Schedule Of Effec

Income Taxes (Schedule Of Effective Income Tax Rate) (Details)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Statutory rate	(35.00%)	(35.00%)	(35.00%)
SEACOR Holdings share awards to Company personnel	2.30%	0.40%	0.10%
Non-deductible expenses	1.80%	0.10%	1.80%
Noncontrolling interests	1.70%	0.20%	(0.50%)
U.S. federal income tax statutory changes	(37.30%)	0.00%	0.00%
Exclusion of foreign subsidiaries with accumulated losses	2.70%	1.10%	0.50%
State taxes	(0.20%)	(0.30%)	0.50%
Other	0.40%	0.10%	0.30%
Effective Income Tax Rate	(63.60%)	(33.40%)	(32.30%)

Income Taxes (Components Of The

Income Taxes (Components Of The Net Deferred Income Tax Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Components of Deferred Tax Assets and Liabilities [Abstract]
Property and Equipment	$ 55,262	$ 98,654
Unremitted earnings of foreign subsidiaries	0	24,084
Investments in 50% or Less Owned Companies	4,258	15,203
Other	5,901	2,260
Total deferred tax liabilities	65,421	140,201
Federal net operating loss carryforwards	5,111	0
Other	5,373	15,256
Total deferred tax assets	10,484	15,256
Valuation allowance	(569)	0
Deferred Tax Assets, Net of Valuation Allowance	9,915	15,256
Net deferred tax liabilities	$ 55,506	$ 124,945

Derivative Instruments And He66

Derivative Instruments And Hedging Strategies (Narrative) (Details) $ in Thousands, € in Millions	12 Months Ended
	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Dec. 31, 2017EUR (€)	Sep. 30, 2017
Derivative [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	3.75%			3.75%
Derivative (gains) losses on cash flow hedges		$ (2,493)
Cash Flow Hedging [Member]
Derivative [Line Items]
Derivative (gains) losses on cash flow hedges	$ 214	(2,500)	$ (1,193)
Fixed interest rate	0.027%			0.027%
Derivative, Notional Amount	$ 18,000			€ 15
Sea-Cat Crewzer II [Member] | Cash Flow Hedging [Member]
Derivative [Line Items]
Fixed interest rate	1.52%			1.52%
Derivative, Notional Amount	$ 20,900
Sea Cat Crewzer [Member] | Cash Flow Hedging [Member]
Derivative [Line Items]
Fixed interest rate	1.52%			1.52%
Derivative, Notional Amount	$ 18,500
MexMar [Member] | Cash Flow Hedging [Member]
Derivative [Line Items]
Derivative, Notional Amount	$ 110,800
Not Designated as Hedging Instrument [Member] | Falcon Global [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Fixed interest rate	2.06%			2.06%
Derivative, Notional Amount	$ 56,300
Not Designated as Hedging Instrument [Member] | OSV Partners [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, Notional Amount	$ 33,000
Not Designated as Hedging Instrument [Member] | Dynamic Offshore Drilling Ltd. [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Fixed interest rate	1.30%			1.30%
Derivative, Notional Amount	$ 64,200
Three Point Seven Five Percentage Convertible Notes [Member]
Derivative [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	3.75%			3.75%	3.75%
Minimum [Member] | MexMar [Member] | Cash Flow Hedging [Member]
Derivative [Line Items]
Fixed interest rate	1.71%			1.71%
Minimum [Member] | Not Designated as Hedging Instrument [Member] | OSV Partners [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Fixed interest rate	1.89%			1.89%
Maximum [Member] | MexMar [Member] | Cash Flow Hedging [Member]
Derivative [Line Items]
Fixed interest rate	2.10%			2.10%
Maximum [Member] | Not Designated as Hedging Instrument [Member] | OSV Partners [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Fixed interest rate	2.27%			2.27%
Construction in Progress [Member] | Fair Value Hedging [Member]
Derivative [Line Items]
Change in Unrealized Gain (Loss) on Hedged Item in Fair Value Hedge	$ 100	$ 800

Derivative Instruments And He67

Derivative Instruments And Hedging Strategies (Fair Values Of Derivative Instruments) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Sep. 30, 2017	Dec. 31, 2016	Dec. 01, 2015
Derivatives, Fair Value [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	3.75%
Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset	$ 260		$ 0
Derivative Liability	20		389
Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset	419		195
Derivative Liability	6,898		547
Embedded Derivative, Fair Value of Embedded Derivative Asset	0		0
Embedded Derivative, Fair Value of Embedded Derivative Liability	6,832		0
Foreign Exchange [Member] | Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset	0		0
Derivative Liability	0		316
Foreign Exchange [Member] | Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset	0		195
Derivative Liability	0		158
Interest Rate Swap [Member] | Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset	260		0
Derivative Liability	20		73
Interest Rate Swap [Member] | Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset	159		0
Derivative Liability	$ 46		$ 0
Three Point Seven Five Percentage Convertible Notes [Member]
Derivatives, Fair Value [Line Items]
Embedded Derivative, Fair Value of Embedded Derivative Liability				$ 27,300
Debt Instrument, Interest Rate, Stated Percentage	3.75%	3.75%

Derivative Instruments And He68

Derivative Instruments And Hedging Strategies (Recognized Gains (Losses) On Derivative Instruments Not Designated As Hedging Instruments) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Derivative [Line Items]
Derivative (gains) losses on cash flow hedges		$ (2,493,000)
Derivative gains (losses), net	$ 20,256	2,995	$ (2,766)
Cash Flow Hedging [Member]
Derivative [Line Items]
Derivative (gains) losses on cash flow hedges	214,000	(2,500,000)	(1,193,000)
Fair Value Hedging [Member] | Construction in Progress [Member]
Derivative [Line Items]
Change in Unrealized Gain (Loss) on Hedged Item in Fair Value Hedge	100,000	800,000
Interest Rate Swap [Member]
Derivative [Line Items]
Derivative gains (losses), net	46	(18)	(18)
Equity Option [Member]
Derivative [Line Items]
Derivative gains (losses), net	0	3,095	(2,748)
Foreign Exchange Forward [Member]
Derivative [Line Items]
Derivative gains (losses), net	(212)	(82)	0
Three Point Seven Five Percentage Convertible Notes [Member]
Derivative [Line Items]
Embedded Derivative, Gain on Embedded Derivative	$ 20,422	$ 0	$ 0

Fair Value Measurements (Financ

Fair Value Measurements (Financial Assets And Liabilities Measured At Fair Value On Recurring Basis) (Details) - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Construction Reserve Funds	$ 45,361,000	$ 78,209,000
Exchange Option Liability on Subsidiary Convertible Senior Notes	6,832,000	0
Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative instruments (included in other receivables)	0	0
Construction Reserve Funds	45,361,000	78,209,000
Derivative instruments (included in other current liabilities)	0	0
Exchange Option Liability on Subsidiary Convertible Senior Notes	0
Marketable securities		40,139,000
Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative instruments (included in other receivables)	419,000	195,000
Construction Reserve Funds	0	0
Derivative instruments (included in other current liabilities)	66,000	547,000
Exchange Option Liability on Subsidiary Convertible Senior Notes	0
Marketable securities		0
Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative instruments (included in other receivables)	0	0
Construction Reserve Funds	0	0
Derivative instruments (included in other current liabilities)	0	0
Exchange Option Liability on Subsidiary Convertible Senior Notes	$ 6,832,000
Marketable securities		$ 0

Fair Value Measurements (Estima

Fair Value Measurements (Estimated Fair Value Of Other Financial Assets And Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Cash Equivalents, at Carrying Value	$ 110,234	$ 117,309	$ 150,242	$ 104,769
Investment Owned, at Cost	132	132
Debt, Long-term and Short-term, Combined Amount	314,899	238,205
Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	112,551	118,771
Long-term Debt, Fair Value	0	0
Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	0	0
Long-term Debt, Fair Value	291,932	242,404
Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	0	0
Long-term Debt, Fair Value	$ 0	$ 0

Fair Value Measurements (Non-Fi

Fair Value Measurements (Non-Financial Assets And Liabilities Measured At Fair Value) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity Method Investment, Other than Temporary Impairment	$ 8,800	$ 6,900
Offshore Support Vessels [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Asset Impairment Charges	27,500	119,700	$ 7,100
Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity Method Investments, Fair Value Disclosure	0	0
Notes Receivable, Fair Value Disclosure		0
Fair Value, Inputs, Level 1 [Member] | Offshore Support Vessels Anchor Handling Towing Supply [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Property, Plant, and Equipment, Fair Value Disclosure	0	0
Fair Value, Inputs, Level 1 [Member] | Offshore Support Vessels Fast Support [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Property, Plant, and Equipment, Fair Value Disclosure	0	0
Fair Value, Inputs, Level 1 [Member] | Offshore Support Vessels Supply [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Property, Plant, and Equipment, Fair Value Disclosure		0
Fair Value, Inputs, Level 1 [Member] | Offshore Support Vessels Specialty [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Property, Plant, and Equipment, Fair Value Disclosure	0	0
Fair Value, Inputs, Level 1 [Member] | Liftboats [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Property, Plant, and Equipment, Fair Value Disclosure		0
Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity Method Investments, Fair Value Disclosure	20,658	0
Notes Receivable, Fair Value Disclosure		0
Fair Value, Inputs, Level 2 [Member] | Offshore Support Vessels Anchor Handling Towing Supply [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Property, Plant, and Equipment, Fair Value Disclosure	12,400	2,600
Fair Value, Inputs, Level 2 [Member] | Offshore Support Vessels Fast Support [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Property, Plant, and Equipment, Fair Value Disclosure	175	50
Fair Value, Inputs, Level 2 [Member] | Offshore Support Vessels Supply [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Property, Plant, and Equipment, Fair Value Disclosure		2,153
Fair Value, Inputs, Level 2 [Member] | Offshore Support Vessels Specialty [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Property, Plant, and Equipment, Fair Value Disclosure	750	4,000
Fair Value, Inputs, Level 2 [Member] | Liftboats [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Property, Plant, and Equipment, Fair Value Disclosure		0
Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity Method Investments, Fair Value Disclosure	20,430	18,539
Notes Receivable, Fair Value Disclosure		$ 11,900
Fair Value Inputs, Comparability Adjustments		33.00%
Fair Value Inputs, Discount Rate		56.00%
Provision for Loan and Lease Losses		$ 1,800
Fair Value, Inputs, Level 3 [Member] | Falcon Global [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Inputs, Discount Rate		25.00%
Equity Method Investment, Other than Temporary Impairment		$ 6,400
Fair Value, Inputs, Level 3 [Member] | Offshore Support Vessels Anchor Handling Towing Supply [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Property, Plant, and Equipment, Fair Value Disclosure	0	$ 42,500
Fair Value Inputs, Comparability Adjustments		55.00%
Fair Value Inputs, Discount Rate		74.00%
Fair Value, Inputs, Level 3 [Member] | Offshore Support Vessels Fast Support [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Property, Plant, and Equipment, Fair Value Disclosure	0	$ 0
Fair Value, Inputs, Level 3 [Member] | Offshore Support Vessels Supply [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Property, Plant, and Equipment, Fair Value Disclosure		1,800
Fair Value, Inputs, Level 3 [Member] | Offshore Support Vessels Specialty [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Property, Plant, and Equipment, Fair Value Disclosure	$ 0	0
Fair Value, Inputs, Level 3 [Member] | Liftboats [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Property, Plant, and Equipment, Fair Value Disclosure		$ 62,830
Fair Value Inputs, Comparability Adjustments		42.00%
Fair Value Inputs, Discount Rate		61.00%
Cost Approach Valuation Technique [Member] | Fair Value, Inputs, Level 3 [Member] | Offshore Support Vessels Anchor Handling Towing Supply [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Nonrecurring		$ 364,000
Cost Approach Valuation Technique [Member] | Fair Value, Inputs, Level 3 [Member] | Liftboats [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Nonrecurring		$ 279,000

Common Stock (Details)

Common Stock (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Sep. 30, 2017
Equity, Class of Treasury Stock [Line Items]
Contributions from SEACOR Holdings	$ 0	$ 0	$ 6,900
Debt Instrument, Interest Rate, Stated Percentage	3.75%
Financial support received upon issuance of convertible senior notes, net of tax			5,532
Distributions to SEACOR Holdings	$ 0	0	1,845
Three Point Seven Five Percentage Convertible Notes [Member]
Equity, Class of Treasury Stock [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	3.75%			3.75%
Financial support received upon issuance of convertible senior notes, net of tax	$ 0	$ 0	$ (8,511)

Noncontrolling Interests in S73

Noncontrolling Interests in Subsidiaries (Details) $ in Thousands	3 Months Ended									9 Months Ended	12 Months Ended
	Mar. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Sep. 30, 2017USD ($)	Jun. 30, 2017USD ($)	Mar. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Sep. 30, 2016USD ($)	Jun. 30, 2016USD ($)	Mar. 31, 2016USD ($)	Sep. 30, 2017USD ($)	Dec. 31, 2017USD ($)equipment	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Feb. 09, 2018USD ($)
Noncontrolling Interest [Line Items]
Noncontrolling interests in subsidiaries		$ 14,975				$ 5,544					$ 14,975	$ 5,544
Net Income (Loss)		27,904	$ (22,356)	$ (36,489)	$ (7,599)	(61,774)	$ (28,007)	$ (30,789)	$ (12,580)		(38,540)	(133,150)	$ (26,846)
Net Income (Loss) Attributable to Noncontrolling Interest											(5,639)	(1,103)	403
Investments in and advances to 50% or less owned companies											5,469	16,863	24,976
Falcon Global [Member]
Noncontrolling Interest [Line Items]
Noncontrolling interests in subsidiaries		$ 12,087				0					$ 12,087	0
Net Assets			$ 24,200							$ 24,200
Net Income (Loss)										(10,600)
Net Income (Loss) Attributable to Noncontrolling Interest										$ (5,300)
Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners		50.00%									50.00%
Windcat Workboats Ltd. [Member]
Noncontrolling Interest [Line Items]
Noncontrolling interests in subsidiaries		$ 2,608				5,266					$ 2,608	5,266
Net Assets		$ 20,800				21,100					20,800	21,100
Net Income (Loss)											(2,100)	(4,500)
Net Income (Loss) Attributable to Noncontrolling Interest											$ (400)	(1,100)
Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners		12.50%									12.50%
Business Acquisition, Percentage of Voting Interests Acquired			12.50%							12.50%
Investments in and advances to 50% or less owned companies										$ 3,700
Other Noncontrolling Interests [Member]
Noncontrolling Interest [Line Items]
Noncontrolling interests in subsidiaries		$ 280				278					$ 280	278
Liftboats [Member] | Falcon Global [Member]
Noncontrolling Interest [Line Items]
Number of Equipment Operated | equipment											2
Minimum [Member] | Other Noncontrolling Interests [Member]
Noncontrolling Interest [Line Items]
Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners		1.80%									1.80%
Maximum [Member] | Other Noncontrolling Interests [Member]
Noncontrolling Interest [Line Items]
Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners		30.00%									30.00%
Falcon Global [Member]
Noncontrolling Interest [Line Items]
Secured Long-term Debt, Noncurrent		$ 54,870				$ 0					$ 54,870	$ 0
Subsequent Event [Member] | Falcon Global [Member]
Noncontrolling Interest [Line Items]
Repayments of Long-term Debt	$ 15,000
Line of Credit Facility, Maximum Borrowing Capacity														$ 15,000
Debt Instrument, Face Amount														131,100
Secured Long-term Debt, Noncurrent														$ 116,100
Noncontrolling Interest, Ownership Percentage by Parent														72.00%
Proceeds from Lines of Credit	$ 5,000
Offshore Marine Services [Member] | Windcat Workboats Ltd. [Member]
Noncontrolling Interest [Line Items]
Net Income (Loss)													1,600
Net Income (Loss) Attributable to Noncontrolling Interest													$ 400

Savings Plans And Multiemploy74

Savings Plans And Multiemployer Pension Plans (Details) £ in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2017USD ($)	Dec. 31, 2015USD ($)	Dec. 31, 2015GBP (£)	Dec. 31, 2014USD ($)	Dec. 31, 2013USD ($)	Dec. 31, 2014GBP (£)
Defined Benefit Plan Disclosure [Line Items]
Employer Matching Contribution Percent of Employees' Gross Pay		3.50%	3.50%
Defined Contribution Plan Contributions		$ 1.3
United Kingdom Merchant Navy Officers Pension Fund [Member] | Foreign Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Pension and other postretirement benefit expense					$ 19.4
United Kingdom Merchant Navy Ratings Pension Fund [Member] | Foreign Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Pension and other postretirement benefit expense		$ 6.9	£ 4.5	$ 0.4
Pension and other postretirement benefit plans, total funding deficit				$ 491.7		£ 325
Other Defined Contribution Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Contribution Plan Contributions	$ 0.7

Share Based Compensation (Narra

Share Based Compensation (Narrative) (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock authorized for grant under the Share Incentive Plans		2,174,000
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant	1,556,300
Adjustments to Additional Paid in Capital, Other	$ (2,656)
Additional compensation expense	800
Unrecognized compensation costs	5,200
Compensation costs expected to be recognized in 2018	1,700
Compensation costs expected to be recognized in 2019	$ 1,400
Weighted average expected volatility	52.50%
Weighted average discount rates	2.22%
Expected lives	6 years
Weighted average remaining contractual term for total outstanding stock options	9 years 328 days
Employee Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock authorized for grant under the Share Incentive Plans	300,000
Share-based Compensation Arrangement by Share-based Payment Award, Discount from Market Price, Purchase Date	85.00%
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Adjustments to Additional Paid in Capital, Other	$ 2,700
Stock Issued During Period, Shares, Restricted Stock Award, Gross	120,693
Weighted average values of grants	$ 12.50
Restricted Stock [Member] | Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock and restricted stock units vesting period	1 year
Restricted Stock [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock and restricted stock units vesting period	4 years
Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average values of grants	$ 6.41
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price	$ 12.50
Employee Stock Option [Member] | Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock and restricted stock units vesting period	1 year
Employee Stock Option [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock and restricted stock units vesting period	4 years
SEACOR Holdings Inc. [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Additional compensation expense	$ 1,700
SEACOR Holdings Inc. [Member] | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Additional compensation expense	$ 600

Share Based Compensation (Share

Share Based Compensation (Share Based Compensation Plans) (Details) - shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock Option, Outstanding as of December 31,	613,700	0
Total Options, Granted, Number of Shares	613,700
Stock Options, Exercised, Number of Shares	0
Stock Options, Forfeited, Number of Shares	0
Stock Options, Expired, Number of Shares	0
Director [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Director stock awards granted	3,000
Restricted Stock [Member]
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, Nonvested, Number	121,693	0
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period	1,000
Restricted stock awards granted	120,693
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period	0
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period	0

Related Party Transactions (Det

Related Party Transactions (Details) - USD ($)	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Related Party Transaction [Line Items]
Related party transaction, amounts	$ 9,400,000	$ 11,214	$ 12,655	$ 78,100
Adjustments to Additional Paid in Capital, Other		$ (2,656,000)
Employer Matching Contribution Percent of Employees' Gross Pay				3.50%
Related Party Transaction, Rate		0.50%
Interest Expense, Related Party		$ 300,000	400,000	$ 100,000
Allocated Share-based Compensation Expense		$ 800,000
Debt Instrument, Interest Rate, Stated Percentage		3.75%
OSV Partners [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Revenues from Transactions with Related Party		$ 600,000	500,000	1,200,000
Equity Method Investment, Ownership Percentage		30.40%
Officer [Member] | OSV Partners [Member]
Related Party Transaction [Line Items]
Partners' Capital Account, Contributions		$ 300,000
Officer [Member] | OSV Partners [Member] | Maximum [Member]
Related Party Transaction [Line Items]
Partners' Capital Account, Contributions		1,500,000
General Partners' Capital Account		300,000
Transition Services Agreement [Member]
Related Party Transaction [Line Items]
Related party transaction, amounts		3,300,000
Transition Services Agreement [Member] | Maximum [Member]
Related Party Transaction [Line Items]
Related party transaction, amounts		6,300,000
Payroll Services [Member]
Related Party Transaction [Line Items]
Related party transaction, amounts		0	0	57,939
Health Insurance [Member]
Related Party Transaction [Line Items]
Related party transaction, amounts		899	3,702	7,249
Other Pension Plan, Postretirement or Supplemental Plans [Member]
Related Party Transaction [Line Items]
Related party transaction, amounts		0	0	1,876
Stock Compensation Plan [Member]
Related Party Transaction [Line Items]
Related party transaction, amounts		8,383	4,588	4,730
Management Services [Member]
Related Party Transaction [Line Items]
Related party transaction, amounts		1,932	$ 4,365	6,306
Management Services [Member] | Maximum [Member]
Related Party Transaction [Line Items]
Related party transaction, amounts				7,700,000
SEACOR Holdings Inc. [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Revenues from Transactions with Related Party		100,000
Guarantor Obligations, Maximum Exposure, Undiscounted		69,100,000
Allocated Share-based Compensation Expense		$ 1,700,000
Notes Receivable [Member]
Related Party Transaction [Line Items]
Related party transaction, amounts				13,600,000
Securities (Assets) [Member]
Related Party Transaction [Line Items]
Related party transaction, amounts				$ 36,600,000
Limited Partner [Member] | OSV Partners [Member]
Related Party Transaction [Line Items]
Equity Method Investment, Ownership Percentage		30.40%
Limited Partner [Member] | Officer [Member] | OSV Partners [Member]
Related Party Transaction [Line Items]
Equity Method Investment, Ownership Percentage		30.40%
Limited Partner [Member] | Officer [Member] | OSV Partners [Member] | Maximum [Member]
Related Party Transaction [Line Items]
Equity Method Investment, Ownership Percentage		3.90%
General Partner [Member] | OSV Partners [Member]
Related Party Transaction [Line Items]
Equity Method Investment, Ownership Percentage		38.60%
General Partner [Member] | Officer [Member] | OSV Partners [Member] | Maximum [Member]
Related Party Transaction [Line Items]
Equity Method Investment, Ownership Percentage		5.00%
Restricted Stock [Member]
Related Party Transaction [Line Items]
Stock Issued During Period, Shares, Restricted Stock Award, Gross		120,693
Adjustments to Additional Paid in Capital, Other		$ 2,700,000
Restricted Stock [Member] | SEACOR Holdings Inc. [Member]
Related Party Transaction [Line Items]
Allocated Share-based Compensation Expense		$ 600,000
Share Distribution [Member]
Related Party Transaction [Line Items]
Related party transaction, amounts	$ 6,700,000
Three Point Seven Five Percentage Convertible Notes [Member]
Related Party Transaction [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	3.75%	3.75%
Restructuring Charges [Member]
Related Party Transaction [Line Items]
Related party transaction, amounts	$ 6,000,000
Restructuring Charges [Member] | Maximum [Member]
Related Party Transaction [Line Items]
Related party transaction, amounts	3,000,000
Employee Severance [Member]
Related Party Transaction [Line Items]
Related party transaction, amounts	700,000
General and Administrative Expense [Member]
Related Party Transaction [Line Items]
Related party transaction, amounts	$ 3,400,000

Commitments And Contingencies (

Commitments And Contingencies (Narrative) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)equipment	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Dec. 31, 2018USD ($)equipment
Commitments and Contingencies [Line Items]
Unrecorded Unconditional Purchase Obligation, Due within Two Years | $	$ 21,919
Unrecorded Unconditional Purchase Obligation | $	66,747
Total rental expense for operating leases | $	$ 14,500	$ 19,400	$ 24,500
Offshore Support Vessels Fast Support [Member]
Commitments and Contingencies [Line Items]
Unrecorded Unconditional Purchase Obligation, Maximum Quantity	4
Offshore Support Vessels Supply [Member]
Commitments and Contingencies [Line Items]
Unrecorded Unconditional Purchase Obligation, Maximum Quantity	3
Wind Farm Utility Vessel [Member]
Commitments and Contingencies [Line Items]
Unrecorded Unconditional Purchase Obligation, Maximum Quantity	2
Offshore Support Vessels [Member]
Commitments and Contingencies [Line Items]
Number of equipment leases	7
Subsequent Event [Member]
Commitments and Contingencies [Line Items]
Unrecorded Unconditional Purchase Obligation, Due within Two Years | $				$ 900
Unrecorded Unconditional Purchase Obligation | $				$ 11,000
Subsequent Event [Member] | Offshore Support Vessels Supply [Member]
Commitments and Contingencies [Line Items]
Unrecorded Unconditional Purchase Obligation, Maximum Quantity				2
Subsequent Event [Member] | Wind Farm Utility Vessel [Member]
Commitments and Contingencies [Line Items]
Unrecorded Unconditional Purchase Obligation, Maximum Quantity				2
Maximum [Member]
Commitments and Contingencies [Line Items]
Lessee Leasing Arrangements, Operating Leases, Term of Contract	4 years
Minimum [Member]
Commitments and Contingencies [Line Items]
Lessee Leasing Arrangements, Operating Leases, Term of Contract	1 year

Commitments And Contingencies79

Commitments And Contingencies (Future Minimum Payments Under Operating Leases) (Details) $ in Thousands	Dec. 31, 2017USD ($)
Commitments and Contingencies Disclosure [Abstract]
Total Minimum Payments, 2018	$ 16,525
Total Minimum Payments, 2019	16,525
Total Minimum Payments, 2020	13,460
Total Minimum Payments, 2021	6,143
Total Minimum Payments, 2022	$ 6

Major Customers And Segment I80

Major Customers And Segment Information (Operating Results, Capital Expenditures And Assets By Reportable Segments) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Equity in Earnings (Losses) of 50% or Less Owned Companies									$ 4,077	$ (6,314)	$ 8,757
Operating Revenues	$ (49,343)	$ (47,813)	$ (42,323)	$ (34,304)	$ (44,361)	$ (54,125)	$ (57,271)	$ (59,879)	(173,783)	(215,636)	(368,868)
Operating Expenses									146,651	149,348	253,463
Direct Vessel Profit (Loss)									27,132	66,288	115,405
Depreciation and amortization									62,779	58,069	61,729
Other Cost and Expense, Operating									131,944	124,954	137,323
Operating Income (Loss)	(35,830)	$ (29,129)	$ (44,815)	$ (18,585)	(82,719)	$ (41,068)	$ (34,514)	$ (16,587)	(128,359)	(174,888)	(38,935)
Property, Plant and Equipment, Gross	1,179,836				958,759				1,179,836	958,759	1,102,619
Accumulated depreciation	(560,160)				(540,619)				(560,160)	(540,619)	(546,962)
Property, Plant and Equipment, Net In Service	619,676				418,140				619,676	418,140	555,657
Administrative and general									56,217	49,308	53,085
Losses on Asset Dispositions and Impairments, Net									(23,547)	(116,222)	(17,017)
Personnel [Member]
Segment Reporting Information [Line Items]
Operating Expenses									81,500	95,144	150,606
Repairs and maintenance [Member]
Segment Reporting Information [Line Items]
Operating Expenses									27,655	21,282	36,371
Drydocking [Member]
Segment Reporting Information [Line Items]
Operating Expenses									9,035	7,821	17,781
Insurance and loss reserves [Member]
Segment Reporting Information [Line Items]
Operating Expenses									6,524	5,682	9,898
Fuel, lubes and supplies [Member]
Segment Reporting Information [Line Items]
Operating Expenses									12,032	12,088	20,762
Other [Member]
Segment Reporting Information [Line Items]
Operating Expenses									9,905	7,331	18,045
Leased-in equipment [Member]
Segment Reporting Information [Line Items]
Operating Expenses									12,948	17,577	22,509
Time Charter Revenues [Member]
Segment Reporting Information [Line Items]
Operating Revenues									(160,545)	(186,327)	(330,890)
Bareboat Charter Revenues [Member]
Segment Reporting Information [Line Items]
Operating Revenues									(4,636)	(8,833)	(8,598)
Other Marine Services Revenues [Member]
Segment Reporting Information [Line Items]
Operating Revenues									(8,602)	(20,476)	(29,380)
United States (primarily Gulf of Mexico) [Member]
Segment Reporting Information [Line Items]
Operating Revenues									(22,296)	(32,856)	(118,751)
Operating Expenses									26,063	30,280	84,404
Direct Vessel Profit (Loss)									(3,767)	2,576	34,347
Depreciation and amortization									22,060	27,052	26,605
Property, Plant and Equipment, Gross	410,475				404,226				410,475	404,226	447,862
Accumulated depreciation	230,636				233,075				230,636	233,075	198,556
Property, Plant and Equipment, Net In Service	179,839				171,151				179,839	171,151	249,306
United States (primarily Gulf of Mexico) [Member] | Personnel [Member]
Segment Reporting Information [Line Items]
Operating Expenses									15,621	22,305	52,843
United States (primarily Gulf of Mexico) [Member] | Repairs and maintenance [Member]
Segment Reporting Information [Line Items]
Operating Expenses									3,594	2,721	8,697
United States (primarily Gulf of Mexico) [Member] | Drydocking [Member]
Segment Reporting Information [Line Items]
Operating Expenses									1,828	228	6,430
United States (primarily Gulf of Mexico) [Member] | Insurance and loss reserves [Member]
Segment Reporting Information [Line Items]
Operating Expenses									3,286	3,363	5,193
United States (primarily Gulf of Mexico) [Member] | Fuel, lubes and supplies [Member]
Segment Reporting Information [Line Items]
Operating Expenses									1,485	1,392	6,785
United States (primarily Gulf of Mexico) [Member] | Other [Member]
Segment Reporting Information [Line Items]
Operating Expenses									249	271	4,456
United States (primarily Gulf of Mexico) [Member] | Leased-in equipment [Member]
Segment Reporting Information [Line Items]
Operating Expenses									8,152	7,975	10,891
United States (primarily Gulf of Mexico) [Member] | Time Charter Revenues [Member]
Segment Reporting Information [Line Items]
Operating Revenues									(18,079)	(28,902)	(111,892)
United States (primarily Gulf of Mexico) [Member] | Bareboat Charter Revenues [Member]
Segment Reporting Information [Line Items]
Operating Revenues									0	0	0
United States (primarily Gulf of Mexico) [Member] | Other Marine Services Revenues [Member]
Segment Reporting Information [Line Items]
Operating Revenues									(4,217)	(3,954)	(6,859)
Africa Primarily West Africa [Member]
Segment Reporting Information [Line Items]
Operating Revenues									(33,946)	(37,562)	(57,252)
Operating Expenses									28,367	21,924	29,081
Direct Vessel Profit (Loss)									5,579	15,638	28,171
Depreciation and amortization									9,280	6,720	8,580
Property, Plant and Equipment, Gross	192,600				136,428				192,600	136,428	144,880
Accumulated depreciation	57,228				60,794				57,228	60,794	71,965
Property, Plant and Equipment, Net In Service	135,372				75,634				135,372	75,634	72,915
Africa Primarily West Africa [Member] | Personnel [Member]
Segment Reporting Information [Line Items]
Operating Expenses									13,419	12,628	15,677
Africa Primarily West Africa [Member] | Repairs and maintenance [Member]
Segment Reporting Information [Line Items]
Operating Expenses									5,957	2,628	4,692
Africa Primarily West Africa [Member] | Drydocking [Member]
Segment Reporting Information [Line Items]
Operating Expenses									2,180	1,098	757
Africa Primarily West Africa [Member] | Insurance and loss reserves [Member]
Segment Reporting Information [Line Items]
Operating Expenses									677	539	1,165
Africa Primarily West Africa [Member] | Fuel, lubes and supplies [Member]
Segment Reporting Information [Line Items]
Operating Expenses									2,815	2,512	2,705
Africa Primarily West Africa [Member] | Other [Member]
Segment Reporting Information [Line Items]
Operating Expenses									3,319	2,519	4,085
Africa Primarily West Africa [Member] | Leased-in equipment [Member]
Segment Reporting Information [Line Items]
Operating Expenses									3,870	3,898	4,695
Africa Primarily West Africa [Member] | Time Charter Revenues [Member]
Segment Reporting Information [Line Items]
Operating Revenues									(32,866)	(36,706)	(53,724)
Africa Primarily West Africa [Member] | Bareboat Charter Revenues [Member]
Segment Reporting Information [Line Items]
Operating Revenues									0	0	0
Africa Primarily West Africa [Member] | Other Marine Services Revenues [Member]
Segment Reporting Information [Line Items]
Operating Revenues									(1,080)	(856)	(3,528)
Middle East and Asia [Member]
Segment Reporting Information [Line Items]
Operating Revenues									(33,884)	(53,887)	(63,492)
Operating Expenses									37,299	35,117	44,364
Direct Vessel Profit (Loss)									(3,415)	18,770	19,128
Depreciation and amortization									17,724	11,550	11,209
Property, Plant and Equipment, Gross	326,378				197,389				326,378	197,389	218,927
Accumulated depreciation	100,435				97,433				100,435	97,433	88,722
Property, Plant and Equipment, Net In Service	225,943				99,956				225,943	99,956	130,205
Middle East and Asia [Member] | Personnel [Member]
Segment Reporting Information [Line Items]
Operating Expenses									16,883	18,381	20,614
Middle East and Asia [Member] | Repairs and maintenance [Member]
Segment Reporting Information [Line Items]
Operating Expenses									9,037	6,426	8,678
Middle East and Asia [Member] | Drydocking [Member]
Segment Reporting Information [Line Items]
Operating Expenses									968	2,117	1,275
Middle East and Asia [Member] | Insurance and loss reserves [Member]
Segment Reporting Information [Line Items]
Operating Expenses									1,444	731	1,448
Middle East and Asia [Member] | Fuel, lubes and supplies [Member]
Segment Reporting Information [Line Items]
Operating Expenses									3,727	4,215	5,033
Middle East and Asia [Member] | Other [Member]
Segment Reporting Information [Line Items]
Operating Expenses									5,240	3,247	7,316
Middle East and Asia [Member] | Leased-in equipment [Member]
Segment Reporting Information [Line Items]
Operating Expenses									862	4,389	4,364
Middle East and Asia [Member] | Time Charter Revenues [Member]
Segment Reporting Information [Line Items]
Operating Revenues									(33,410)	(41,657)	(48,541)
Middle East and Asia [Member] | Bareboat Charter Revenues [Member]
Segment Reporting Information [Line Items]
Operating Revenues									0	0	0
Middle East and Asia [Member] | Other Marine Services Revenues [Member]
Segment Reporting Information [Line Items]
Operating Revenues									(474)	(12,230)	(14,951)
Brazil, Mexico, Central and South America [Member]
Segment Reporting Information [Line Items]
Operating Revenues									(8,165)	(10,209)	(27,785)
Operating Expenses									1,739	2,527	12,559
Direct Vessel Profit (Loss)									6,426	7,682	15,226
Depreciation and amortization									3,608	4,083	5,623
Property, Plant and Equipment, Gross	72,484				57,744				72,484	57,744	87,612
Accumulated depreciation	37,281				34,455				37,281	34,455	48,303
Property, Plant and Equipment, Net In Service	35,203				23,289				35,203	23,289	39,309
Brazil, Mexico, Central and South America [Member] | Personnel [Member]
Segment Reporting Information [Line Items]
Operating Expenses									809	2,117	7,406
Brazil, Mexico, Central and South America [Member] | Repairs and maintenance [Member]
Segment Reporting Information [Line Items]
Operating Expenses									274	232	1,237
Brazil, Mexico, Central and South America [Member] | Drydocking [Member]
Segment Reporting Information [Line Items]
Operating Expenses									0	0	1,859
Brazil, Mexico, Central and South America [Member] | Insurance and loss reserves [Member]
Segment Reporting Information [Line Items]
Operating Expenses									316	43	535
Brazil, Mexico, Central and South America [Member] | Fuel, lubes and supplies [Member]
Segment Reporting Information [Line Items]
Operating Expenses									223	21	673
Brazil, Mexico, Central and South America [Member] | Other [Member]
Segment Reporting Information [Line Items]
Operating Expenses									117	114	849
Brazil, Mexico, Central and South America [Member] | Leased-in equipment [Member]
Segment Reporting Information [Line Items]
Operating Expenses									0	913	2,545
Brazil, Mexico, Central and South America [Member] | Time Charter Revenues [Member]
Segment Reporting Information [Line Items]
Operating Revenues									(2,977)	(196)	(17,585)
Brazil, Mexico, Central and South America [Member] | Bareboat Charter Revenues [Member]
Segment Reporting Information [Line Items]
Operating Revenues									(4,636)	(8,833)	(8,598)
Brazil, Mexico, Central and South America [Member] | Other Marine Services Revenues [Member]
Segment Reporting Information [Line Items]
Operating Revenues									(552)	(1,180)	(1,602)
Europe Primarily North Sea [Member]
Segment Reporting Information [Line Items]
Operating Revenues									(75,492)	(81,122)	(101,588)
Operating Expenses									53,183	59,500	83,055
Direct Vessel Profit (Loss)									22,309	21,622	18,533
Depreciation and amortization									10,107	8,664	9,712
Property, Plant and Equipment, Gross	177,899				162,972				177,899	162,972	203,338
Accumulated depreciation	134,580				114,862				134,580	114,862	139,416
Property, Plant and Equipment, Net In Service	$ 43,319				$ 48,110				43,319	48,110	63,922
Europe Primarily North Sea [Member] | Personnel [Member]
Segment Reporting Information [Line Items]
Operating Expenses									34,768	39,713	54,066
Europe Primarily North Sea [Member] | Repairs and maintenance [Member]
Segment Reporting Information [Line Items]
Operating Expenses									8,793	9,275	13,067
Europe Primarily North Sea [Member] | Drydocking [Member]
Segment Reporting Information [Line Items]
Operating Expenses									4,059	4,378	7,460
Europe Primarily North Sea [Member] | Insurance and loss reserves [Member]
Segment Reporting Information [Line Items]
Operating Expenses									801	1,006	1,557
Europe Primarily North Sea [Member] | Fuel, lubes and supplies [Member]
Segment Reporting Information [Line Items]
Operating Expenses									3,782	3,948	5,566
Europe Primarily North Sea [Member] | Other [Member]
Segment Reporting Information [Line Items]
Operating Expenses									980	1,180	1,339
Europe Primarily North Sea [Member] | Leased-in equipment [Member]
Segment Reporting Information [Line Items]
Operating Expenses									64	402	14
Europe Primarily North Sea [Member] | Time Charter Revenues [Member]
Segment Reporting Information [Line Items]
Operating Revenues									(73,213)	(78,866)	(99,148)
Europe Primarily North Sea [Member] | Bareboat Charter Revenues [Member]
Segment Reporting Information [Line Items]
Operating Revenues									0	0	0
Europe Primarily North Sea [Member] | Other Marine Services Revenues [Member]
Segment Reporting Information [Line Items]
Operating Revenues									$ (2,279)	$ (2,256)	$ (2,440)

Major Customers And Segment I81

Major Customers And Segment Information Major Customers And Segment Information (Narrrative) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Investments, at Equity, and Advances to 50% or Less Owned Companies	$ 92,169				$ 138,311				$ 92,169	$ 138,311
Operating Revenues	49,343	$ 47,813	$ 42,323	$ 34,304	$ 44,361	$ 54,125	$ 57,271	$ 59,879	173,783	215,636	$ 368,868
Equity in Earnings (Losses) of 50% or Less Owned Companies									$ 4,077	$ (6,314)	8,757
Non-US [Member]
Concentration Risk, Percentage									15.15%	13.20%
Operating Revenues									$ 26,800	$ 28,400
Equity in Earnings (Losses) of 50% or Less Owned Companies									$ 1,900	$ (4,200)	$ 8,600
Sales Revenue, Net [Member]
Concentration Risk, Percentage									59.00%	58.00%	55.00%
Sales Revenue, Net [Member] | Non-US [Member]
Concentration Risk, Percentage									87.00%	85.00%	68.00%
MexMar [Member]
Investments, at Equity, and Advances to 50% or Less Owned Companies	61,000								$ 61,000
Equity in Earnings (Losses) of 50% or Less Owned Companies									10,103	$ 3,556	$ 5,650
Other Affiliates [Member]
Investments, at Equity, and Advances to 50% or Less Owned Companies	$ 31,200								31,200
Equity in Earnings (Losses) of 50% or Less Owned Companies									$ (6,026)	$ (9,870)	$ 3,107

Supplemental Information For 82

Supplemental Information For Statements Of Cash Flows (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Income taxes refunded	$ 33,773	$ 10,224	$ 1,667
Interest paid, excluding capitalized interest	9,216	2,698	22,407
Transfer to Investments	1,000	0	0
Services and Equipment received to settle notes receivable	0	0	2,500
Adjustments to Additional Paid in Capital, Equity Component of Convertible Debt			(5,532)
Property, Plant and Equipment [Member]
Property, Plant and Equipment [Line Items]
Services and Equipment received to settle notes receivable	0	11,900	0
Three Point Seven Five Percentage Convertible Notes [Member]
Property, Plant and Equipment [Line Items]
Adjustments to Additional Paid in Capital, Equity Component of Convertible Debt	$ 0	$ 0	$ 8,511

Quarterly Financial Informati83

Quarterly Financial Information (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Quarterly Financial Data [Abstract]
Operating Revenues	$ 49,343	$ 47,813	$ 42,323	$ 34,304	$ 44,361	$ 54,125	$ 57,271	$ 59,879	$ 173,783	$ 215,636	$ 368,868
Operating Loss	(35,830)	(29,129)	(44,815)	(18,585)	(82,719)	(41,068)	(34,514)	(16,587)	(128,359)	(174,888)	(38,935)
Net Income (Loss)	27,904	(22,356)	(36,489)	(7,599)	(61,774)	(28,007)	(30,789)	(12,580)	(38,540)	(133,150)	(26,846)
Net Income (Loss) attributable to SEACOR Marine Holdings Inc.	$ 28,961	$ (20,475)	$ (33,992)	$ (7,395)	$ (61,575)	$ (27,933)	$ (30,580)	$ (11,959)	$ (32,901)	$ (132,047)	$ (27,249)
Basic Earnings (Loss) Per Common Share of SEACOR Marine Holdings Inc.	$ 1.65	$ (1.17)	$ (1.93)	$ (0.42)					$ (1.87)	$ (7.47)	$ (1.54)
Diluted Earnings (Loss) Per Common Share of SEACOR Marine Holdings Inc.	$ 1.20	$ (1.25)	$ (1.93)	$ (0.42)

Valuation And Qualifying Acco84

Valuation And Qualifying Accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Valuation and Qualifying Accounts [Abstract]
Balance Beginning of Year	$ 5,359	$ 1,177	$ 1,177
Bad debt expense (income)	(1,283)	4,280	0
Deductions	37	98	0
Balance End of Year	$ 4,039	$ 5,359	$ 1,177