International Seaways (INSW) 10-K 12 Mar 21 2020 FY Annual report Financial data

Document And Entity Information

Document And Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2020	Mar. 08, 2021	Jun. 30, 2020
Document Type	10-K
Document Annual Report	true
Document Transition Report	false
Document Period End Date	Dec. 31, 2020
Entity Registrant Name	INTERNATIONAL SEAWAYS, INC.
Entity Incorporation, State or Country Code	1T
Entity File Number	1-37836-1
Entity Tax Identification Number	98-0467117
Entity Address, Address Line One	600 Third Avenue
Entity Address, Address Line Two	39th Floor
Entity Address, City or Town	New York
Entity Address, State or Province	NY
Entity Address, Postal Zip Code	10016
City Area Code	212
Local Phone Number	578-1600
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	true
Entity Ex Transition Period	true
Entity Shell Company	false
Entity Public Float			$ 385,512,676
Entity Common Stock, Shares Outstanding		28,014,877
Entity Central Index Key	0001679049
Current Fiscal Year End Date	--12-31
Document Fiscal Period Focus	FY
Document Fiscal Year Focus	2020
Amendment Flag	false
ICFR Auditor Attestation Flag	true
Common Stock [Member]
Title of 12(b) Security	Common Stock (no par value)
Trading Symbol	INSW
Security Exchange Name	NYSE
8.5% Senior Notes [Member]
Title of 12(b) Security	8.5% Senior Notes due 2023
Trading Symbol	INSW - PA
Security Exchange Name	NYSE

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Current Assets:
Cash and cash equivalents	$ 199,390	$ 89,671
Voyage receivables, net of allowance for credit losses of $55 and $1,245, including unbilled of $38,430 and $74,355	43,362	83,845
Other receivables	4,479	3,938
Inventories	3,601	3,896
Prepaid expenses and other current assets	6,002	5,994
Total Current Assets	256,834	187,344
Restricted cash	16,287	60,572
Vessels and other property, less accumulated depreciation	1,108,214	1,292,516
Deferred drydock expenditures, net	36,334	23,125
Operating lease right-of-use assets	21,588	33,718
Investments in and advances to affiliated companies	141,924	153,292
Long-term derivative asset	2,129
Other assets	3,229	2,934
Total Assets	1,586,539	1,753,501
Current Liabilities:
Accounts payable, accrued expenses and other current liabilities	34,425	27,554
Current portion of operating lease liabilities	8,867	12,958
Current installments of long-term debt	61,483	70,350
Current portion of derivative liability	4,121	3,614
Total Current Liabilities	108,896	114,476
Long-term operating lease liabilities	10,253	17,953
Long-term debt	474,332	590,745
Long-term derivative liability	6,155	6,545
Other liabilities	14,861	1,489
Total Liabilities	614,497	731,208
Commitments and contingencies
Equity:
Capital - 100,000,000 no par value shares authorized; 28,014,877 and 29,274,452 shares issued and outstanding	1,280,501	1,313,178
Accumulated deficit	(275,846)	(270,315)
Stockholders Equity Subtotal	1,004,655	1,042,863
Accumulated other comprehensive loss	(32,613)	(20,570)
Total Equity	972,042	1,022,293
Total Liabilities and Equity	$ 1,586,539	$ 1,753,501

CONSOLIDATED BALANCE SHEETS (Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
CONSOLIDATED BALANCE SHEETS [Abstract]
Unbilled voyage receivable (in dollars)	$ 38,430	$ 74,355
Voyage receivables, allowance for credit losses	$ 55	$ 1,245
Common stock, shares authorized	100,000,000	100,000,000
Common stock, no par value	$ 0	$ 0
Common stock, shares, issued	28,014,877	29,274,452
Common stock, shares, outstanding	28,014,877	29,274,452

CONSOLIDATED STATEMENTS OF OPER

CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Shipping Revenues:
Shipping revenues	$ 421,648	$ 366,184	$ 270,361
Operating Expenses:
Voyage expenses	19,643	26,265	27,261
Vessel expenses	128,373	123,205	135,003
Charter hire expenses	30,114	57,512	44,910
Depreciation and amortization	74,343	75,653	72,428
General and administrative	29,047	26,798	24,304
Provision for credit losses, net	(71)	1,245
Third-party debt modification fees	232	30	1,306
Loss on disposal of vessels and other property, including impairments	100,087	308	19,680
Total operating expenses	381,768	311,016	324,892
Income/(loss) from vessel operations	39,880	55,168	(54,531)
Equity in income of affiliated companies	4,119	11,213	29,432
Operating income/(loss)	43,999	66,381	(25,099)
Other expense	(12,817)	(943)	(3,715)
Income/(loss) before interest expense and income taxes	31,182	65,438	(28,814)
Interest expense	(36,712)	(66,267)	(60,231)
Loss before income taxes	(5,530)	(829)	(89,045)
Income tax (provision)/benefit	(1)	(1)	105
Net loss	$ (5,531)	$ (830)	$ (88,940)
Weighted Average Number of Common Shares Outstanding:
Basic and diluted	28,372,375	29,225,483	29,136,634
Per Share Amounts:
Basic and Diluted net income/(loss) per share	$ (0.20)	$ (0.03)	$ (3.05)
Pool Revenue Leases [Member]
Shipping Revenues:
Shipping revenues	$ 272,980	$ 254,055	$ 177,206
Time and Bareboat Charter Leases [Member]
Shipping Revenues:
Shipping revenues	88,719	27,625	25,961
Voyage Charter Leases [Member]
Shipping Revenues:
Shipping revenues	$ 59,949	$ 84,504	$ 67,194

CONSOLIDATED STATEMENTS OF OP_2

CONSOLIDATED STATEMENTS OF OPERATIONS (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
CONSOLIDATED STATEMENTS OF OPERATIONS [Abstract]
Pool revenues, received from companies accounted for by the equity method	$ 194,258	$ 165,583	$ 94,441

CONSOLIDATED STATEMENTS OF COMP

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME/(LOSS) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME [Abstract]
Net loss	$ (5,531)	$ (830)	$ (88,940)
Other Comprehensive (Loss)/Income, net of tax:
Net change in unrealized losses on cash flow hedges	(12,366)	9,788	7,469
Defined benefit pension and other postretirement benefit plans:
Net change in unrecognized prior service costs	46	32	(13)
Net change in unrecognized actuarial losses	277	(461)	3,022
Other Comprehensive (Loss)/Income, net of tax	(12,043)	9,359	10,478
Comprehensive (Loss)/Income	$ (17,574)	$ 8,529	$ (78,462)

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Cash Flows from Operating Activities:
Net loss	$ (5,531)	$ (830)	$ (88,940)
Items included in net loss not affecting cash flows:
Depreciation and amortization	74,343	75,653	72,428
Loss on write-down of vessels and other assets	103,022		19,037
Amortization of debt discount and other deferred financing costs	2,898	6,920	6,212
Deferred financing costs write-off	13,073	3,558	2,400
Stock compensation	5,631	4,278	3,162
Earnings of affiliated companies	(4,013)	(30,266)	(29,201)
Release other comprehensive loss upon sale of investment in affiliated companies		21,615
Change in fair value of interest rate collar recorded through earnings	1,271	(923)
Other - net	1,747	1,461	448
Items included in net income related to investing and financing activities:
(Gain)/loss on disposal of vessels and other assets, net	(2,935)	308	643
Gain on sale of investment in affiliated companies		(3,033)
Loss on extinguishment of debt	1,197	1,100	1,295
Cash distributions from affiliated companies	4,644	13,855	43,622
Payments for drydocking	(25,642)	(19,546)	(4,520)
Insurance claims proceeds related to vessel operations	5,238	2,179	5,436
Changes in operating assets and liabilities:
Decrease/(increase) in receivables	40,483	10,778	(36,436)
Increase/(decrease) in deferred revenue	2,995	(25)	(893)
Net change in inventories, prepaid expenses and other current assets and accounts payable, accrued expense, and other current and long-term liabilities	(2,281)	404	(7,173)
Net cash provided by/(used in) operating activities	216,140	87,486	(12,480)
Cash Flows from Investing Activities:
Expenditures for vessels and vessel improvements	(50,049)	(36,607)	(148,946)
Proceeds from disposal of vessels and other property	73,121	15,767	169,292
Expenditures for other property	(507)	(574)	(1,096)
Proceeds from sale of investment in affiliated companies		122,755
Investments in and advances to affiliated companies, net	2,347	2,338	3,679
Repayments of advances from affiliated companies	7,456	4,195	100,780
Net cash provided by investing activities	32,368	107,874	123,709
Cash Flows from Financing Activities:
Issuance of debt, net of issuance and deferred financing costs	362,989	(100)	70,120
Extinguishment of debt	(422,699)	(110,000)	(62,069)
Premium and fees on extinguishment of debt	(205)	(2,092)
Payments on debt	(82,007)	(49,911)	(71,610)
Cash payments on derivatives containing other-than-insignificant financing element	(2,681)
Cash dividends paid	(6,770)
Repurchases of common stock	(29,997)
Cash paid to tax authority upon vesting of stock-based compensation	(1,541)	(369)	(410)
Other - net	(163)	(289)	(222)
Net cash used in by financing activities	(183,074)	(162,761)	(64,191)
Net increase in cash, cash equivalents and restricted cash	65,434	32,599	47,038
Cash, cash equivalents and restricted cash at beginning of year	150,243	117,644	70,606
Cash, cash equivalents and restricted cash at end of year	$ 215,677	$ 150,243	$ 117,644

CONSOLIDATED STATEMENTS OF CHAN

CONSOLIDATED STATEMENTS OF CHANGES IN EQUITY - USD ($) $ in Thousands	Common Stock [Member]Restricted Stock [Member]	Common Stock [Member]Restricted Stock Units (RSUs) [Member]	Common Stock [Member]	Retained Earnings / (Accumulated deficit) [Member]	Accumulated Other Comprehensive Loss [Member]	Restricted Stock [Member]	Restricted Stock Units (RSUs) [Member]	Total
Balance, beginning at Dec. 31, 2017			$ 1,306,606	$ (180,545)	$ (40,407)			$ 1,085,654
Net loss				(88,940)				(88,940)
Other comprehensive income					10,478			10,478
Forfeitures of vested restricted stock awards			(499)					(499)
Compensation relating to restricted stock units or restricted stock awards	$ 860	$ 1,412				$ 860	$ 1,412
Compensation relating to stock option awards			890					890
Balance, ending at Dec. 31, 2018			1,309,269	(269,485)	(29,929)			1,009,855
Net loss				(830)				(830)
Other comprehensive income					9,359			9,359
Forfeitures of vested restricted stock awards			(369)					(369)
Compensation relating to restricted stock units or restricted stock awards	899	2,317				899	2,317
Compensation relating to stock option awards			1,062					1,062
Balance, ending at Dec. 31, 2019			1,313,178	(270,315)	(20,570)			1,022,293
Net loss				(5,531)				(5,531)
Other comprehensive income					(12,043)			(12,043)
Dividends declared and paid			(6,770)					(6,770)
Forfeitures of vested restricted stock awards			(1,541)					(1,541)
Compensation relating to restricted stock units or restricted stock awards	$ 918	$ 3,639				$ 918	$ 3,639
Compensation relating to stock option awards			1,074					1,074
Repurchase of common stock			(29,997)					(29,997)
Balance, ending at Dec. 31, 2020			$ 1,280,501	$ (275,846)	$ (32,613)			$ 972,042

DESCRIPTION OF BUSINESS AND BAS

DESCRIPTION OF BUSINESS AND BASIS OF PRESENTATION	12 Months Ended
	Dec. 31, 2020
DESCRIPTION OF BUSINESS AND BASIS OF PRESENTATION [Abstract]
DESCRIPTION OF BUSINESS AND BASIS OF PRESENTATION	NOTE 1 — DESCRIPTION OF BUSINESS AND BASIS OF PRESENTATION: ​ Nature of the Business ​ International Seaways, Inc. (“INSW”), a Marshall Islands corporation, and its wholly owned subsidiaries (the “Company” or “INSW,” or “we” or “us” or “our”) are engaged primarily in the ocean transportation of crude oil and petroleum products in international markets. The Marshall Islands is the principal flag of registry of the Company’s vessels. The Company’s business is currently organized into two reportable segments: Crude Tankers and Product Carriers. The crude oil fleet is comprised of most major crude oil vessel classes. The products fleet transports refined petroleum product cargoes from refineries to consuming markets characterized by both long and short-haul routes. ​ As of December 31, 2020, the Company’s operating fleet consisted of 36 vessels, 33 of which were owned (including two Floating Storage and Offloading (“FSO”) service vessels in which the Company has joint venture ownership interests), with the remaining vessels chartered-in. The Company’s operating fleet list excludes vessels chartered-in where the duration of the charter was one year or less at inception. Vessels chartered-in may be bareboat charters or time charters. Under either a bareboat charter or time charter, a customer pays a fixed daily or monthly rate for a fixed period of time for use of the vessel. Under a bareboat charter, the customer pays all costs of operating the vessel, including voyage expenses, such as fuel, canal tolls and port charges, and vessel expenses such as crew costs, vessel stores and supplies, lubricating oils, maintenance and repair, insurance and communications associated with operating the vessel. Under a time charter, the customer pays all voyage expenses and the shipowner pays all vessel expenses. ​ Basis of Presentation ​ The accompanying consolidated financial statements include the accounts of the Company and its wholly owned subsidiaries. All intercompany balances and transactions within the Company have been eliminated. Investments in 50% or less owned affiliated companies, in which the Company exercises significant influence, are accounted for by the equity method.

SUMMARY OF SIGNIFICANT ACCOUNTI

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	12 Months Ended
	Dec. 31, 2020
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES [Abstract]
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	NOTE 2 — SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES: 1. Cash and cash equivalents — ​ 2. Concentration of credit risk Leases Revenue from Contracts with Customers ​ With respect to non-operating lease receivables, the Company recognizes as an allowance its estimate of expected credit losses in accordance with ASC 326, Financial Instruments – Credit losses of the counterparty, and their business strategy. We manage our non-operating lease receivable portfolios using delinquency as a key credit quality indicator. The Company performs the following steps in estimating expected losses: (i) gather historical losses over 5 years; (ii) assume outstanding billed amounts over 180 days as additional expected losses; and (iii) make forward-looking adjustments to the expected losses to reflect future economic conditions by comparing credit default swap rates of significant customers over time. In addition, the Company performs individual assessments for customers that do not share risk characteristics with other customers (for example a customer under bankruptcy or a customer with known disputes or collectability issues). ​ The allowance for credit losses is recognized as an allowance or contra-asset and reflects our best estimate of probable losses inherent in the voyage receivables balance. Provisions for credit losses associated with voyage receivables are included in provision for credit losses on the consolidated statements of operations. Activity for allowance for credit losses is summarized as follows: ​ ​ ​ ​ ​ (Dollars in thousands) ​ ​ Allowance for Credit Losses - Voyage Receivables Balance at January 1, 2018 ​ $ — Provision for expected credit losses ​ ​ — Balance at December 31, 2018 ​ ​ — Provision for expected credit losses ​ ​ 1,245 Balance at December 31, 2019 ​ ​ 1,245 Provision for expected credit losses ​ ​ 58 Write-offs charged against the allowance ​ ​ (1,119) Recoveries of amounts previously written off ​ ​ (129) Balance at December 31, 2020 ​ $ 55 ​ We are also exposed to credit losses from off-balance sheet exposures related to guarantees of joint venture debt. See Note 6, “Equity Method Investments,” for more information on these off-balance sheet exposures. ​ During the year ended December 31, 2020, 2019 and 2018, the Company did not have any individual customers who accounted for 10% or more of its revenues apart from the pools in which it participates. The pools in which the Company participates accounted in aggregate 88% of consolidated voyage receivables at December 31, 2020 and December 31, 2019, respectively. ​ 3. Inventories ​ 4. Vessels, vessel lives, deferred drydocking expenditures and other property ​ Interest costs are capitalized to vessels during the period that vessels are under construction. No interest was capitalized during the three years ended December 31, 2020, since the Company had no vessels under construction during this period. ​ Other property, including leasehold improvements, are recorded at cost and amortized on a straight-line basis over the shorter of the terms of the leases or the estimated useful lives of the assets, which range from three ​ Expenditures incurred during a drydocking are deferred and amortized on the straight-line basis over the period until the next scheduled drydocking, which is generally two ​ 5. Impairment of long-lived assets ​ 6. Deferred finance charges Finance charges, excluding original issue discount, incurred in the arrangement and/or amendments resulting in the modification of debt are deferred and amortized to interest expense on either an effective interest method or straight-line basis over the life of the related debt ​ Interest expense relating to the amortization of deferred financing costs amounted to $2.8 million in 2020, $4.8 million in 2019 and $3.9 million in 2018. ​ 7. Revenue and expense recognition ​ Under ASC 842, lease revenue for fixed lease payments is recognized over the lease term on a straight-line basis and lease revenue for variable lease payments (e.g., demurrage) are recognized in the period in which the changes in facts and circumstances on which the variable lease payments are based occur. Initial direct costs are expensed over the lease term on the same basis as lease revenue. The Company has elected the lessor practical expedient to aggregate non-lease components with the associated lease components and to account for the combined components as required by the practical expedient since its primary revenue streams described above meet the conditions required to adopt the practical expedient. Furthermore, the Company has performed a qualitative analysis of each of its primary revenue contract types to determine whether the lease component or the non-lease component is the predominant component of the contract. The Company concluded that the lease component is the predominant component for all of its primary revenue contract types, as the lessee would ascribe more value to the control and use of the underlying vessel rather than to the technical services to operate the vessel which is an add-on service to the lessee. ​ Revenues from time charters are accounted for as fixed rate operating leases with an embedded technical management service component and are recognized ratably over the rental periods of such charters. Bareboat charters are also accounted for as fixed rate operating leases and the associated revenue is recognized ratably over the rental periods of such charters. Voyage charters contain a lease component if the contract (i) specifies a specific vessel asset; and (ii) has terms that allow the charterer to exercise substantive decision-making rights, which have an economic value to the charterer and therefore allow the charterer to direct how and for what purpose the vessel is used. Voyage charter revenues and expenses are recognized ratably over the estimated length of each voyage. For a voyage charter which contains a lease component, revenue and expenses are recognized based on a lease commencement-to-discharge basis and the lease commencement date is the latter of discharge of the previous cargo or voyage charter contract signing. For voyage charters that do not have a lease component, revenue and expenses are recognized based on a load-to-discharge basis. Accordingly, voyage expenses incurred during a vessel’s positioning voyage to a load port in order to serve a customer under a voyage charter not containing a lease are considered costs to fulfill a contract and are deferred and recognized ratably over the load-to-discharge portion of the contract. ​ Under voyage charters, expenses such as fuel, port charges, canal tolls, cargo handling operations and brokerage commissions are paid by the Company whereas, under time and bareboat charters, such voyage costs are paid by the Company’s customers. ​ For the Company’s vessels operating in pools, revenues and voyage expenses are pooled and allocated to each pool’s participants on a time charter equivalent (“TCE”) basis in accordance with an agreed-upon formula. Accordingly, the Company accounts for its agreements with commercial pools as variable rate operating leases. For the pools in which the Company participates, management monitors, among other things, the relative proportion of the Company’s vessels operating in each of the pools to the total number of vessels in each of the respective pools and assesses whether or not the Company’s participation interest in each of the pools is sufficiently significant so as to determine that the Company has effective control of the pool. ​ Demurrage earned during a voyage charter represents variable consideration. The Company estimates demurrage at contract inception using either the expected value or most likely amount approaches. Such estimate is reviewed and updated over the term of the voyage charter contract. ​ The Company recognizes revenues from services in accordance with the provisions of ASC 606. The standard provides a unified model to determine how revenue is recognized. In doing so, the Company makes judgments including identifying performance obligations in the contract, estimating the amount of variable consideration to include in the transaction price, and allocating the transaction price to each performance obligation. Revenues are recognized to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. In determining the appropriate amount of revenue to be recognized as it fulfills its obligations under its agreements, the Company performs the following steps: (i) identification of the promised goods or services in the contract; (ii) determination of whether the promised goods or services are performance obligations, including whether they are distinct in the context of the contract; (iii) measurement of the transaction price, including the constraint on variable consideration; (iv) allocation of the transaction price to the performance obligations based on estimated selling prices; and (v) recognition of revenue when (or as) the Company satisfies each performance obligation. ​ As the Company’s performance obligations are services which are received and consumed by its customers as it performs such services, revenues are recognized over time proportionate to the days elapsed since the service commencement compared to the total days anticipated to complete the service. The minimum duration of services is less than one year for each of the Company’s current contracts. ​ 8. Leases — The Company determines if an arrangement is a lease at inception. Operating leases are included in operating lease right-of-use (“ROU”) assets, current portion of operating lease liabilities, and long-term operating lease liabilities in the Company’s consolidated balance sheets. The Company does not have finance leases. ​ ROU assets represent our right to use an underlying asset for the lease term and lease liabilities represent our obligation to make lease payments arising from the lease. Operating lease ROU assets and liabilities are recognized at commencement date based on the present value of lease payments over the lease term. The operating lease ROU asset also includes any prepaid lease payments made and excludes accrued lease payments and lease incentives. Our lease terms take into consideration options to extend or terminate the lease, or purchase the underlying asset when it is reasonably certain that we will exercise such options. Lease expense for lease payments is recognized on a straight-line basis over the lease term. As most of our leases do not provide an implicit rate, we use our incremental borrowing rate based on the information available at commencement date in determining the present value of lease payments. The Company makes significant judgements and assumptions to estimate its incremental borrowing rate that a lessee would have to pay to borrow on a 100% collateralized basis over a term similar to the lease term and in an amount equal to the lease payments in a similar economic environment. The Company performs the following steps in estimating its incremental borrowing rate: (i) gather observable debt yields of the Company’s recently issued debt facilities; and (ii) make adjustments to the yields of the actual debt facilities to reflect changes in collateral level, terms, the risk-free interest rate, and credit ratings. In addition, the Company performs sensitivity analyses to evaluate the impact of selected discount rates on the estimated lease liability. The Company makes significant judgements and assumptions to separate the lease component from the non-lease component of its time chartered-in vessels. For purposes of determining the standalone selling price of the vessel lease and technical management service components of the Company’s time charters, the Company concluded that the residual approach would be the most appropriate method to use given that vessel lease rates are highly variable depending on shipping market conditions, the duration of such charters, and the age of the vessel. The Company believes that the standalone transaction price attributable to the technical management service component is more readily determinable than the price of the lease component and, accordingly, the price of the service component is estimated using observable data (such as fees charged by third-party technical managers) and the residual transaction price is attributed to the vessel lease component. 9. Derivatives — Derivatives and Hedging ​ The Company formally documents all relationships between hedging instruments and hedged items, as well as its risk-management objective and strategy for undertaking various hedge transactions. This process includes linking all derivatives that are designated as cash flow hedges to forecasted transactions. The Company also formally assesses (both at the hedge’s inception and on an ongoing basis) whether the derivatives that are used in hedging transactions have been highly effective in offsetting changes in the cash flows of hedged items and whether those derivatives may be expected to remain highly effective in future periods. When it is determined that a derivative is not (or has ceased to be) highly effective as a hedge, the Company discontinues hedge accounting prospectively, as discussed below. ​ The Company discontinues hedge accounting prospectively when: (1) it determines that the derivative is no longer effective in offsetting changes in the cash flows of a hedged item such as forecasted transactions; (2) the derivative expires or is sold, terminated, or exercised; (3) it is no longer probable that the forecasted transaction will occur; or (4) management determines that designating the derivative as a hedging instrument is no longer appropriate or desired. ​ When the Company discontinues hedge accounting because it is no longer probable that the forecasted transaction will occur in the originally expected period, the gain or loss on the derivative remains in accumulated other comprehensive income/(loss) and is reclassified into earnings when the forecasted transaction affects earnings. However, if it is probable that a forecasted transaction will not occur by the end of the originally specified time period or within an additional two-month period of time thereafter, the gains and losses that were accumulated in other comprehensive gain/(loss) will be recognized immediately in earnings. In all situations in which hedge accounting is discontinued and the derivative remains outstanding, the Company will carry the derivative at its fair value on the consolidated balance sheets, recognizing changes in the fair value in current-period earnings, unless it is designated in a new hedging relationship. ​ Any gain or loss realized upon the early termination of an interest rate cap, collar or swaps is recognized as an adjustment of interest expense over the shorter of the remaining term of the derivative instruments or the hedged debt. See Note 9, “Fair Value of Financial Instruments, Derivatives and Fair Value Disclosures,” for additional disclosures on the Company’s interest rate cap, collar and swaps and other financial instruments. ​ 10. Fair value measurements — Fair Value Measurement fair value of assets and liabilities should include consideration of non-performance risk, which for the liabilities described below includes the Company's own credit risk. The hierarchy below lists three levels of fair value based on the extent to which inputs used in measuring fair value are observable in the market: ​ Level 1 - Quoted prices in active markets for identical assets or liabilities. Our Level 1 non-derivative assets and liabilities primarily include cash and cash equivalents and the 8.50% Senior Notes. Level 2 - Quoted prices for similar assets and liabilities in active markets or model-based valuation techniques for which all significant inputs are observable in the market (where applicable, these models project future cash flows and discount the future amounts to a present value using market-based observable inputs including interest rate curves, credit spreads, etc.). Our Level 2 non-derivative liabilities primarily include the Core Term Loan Facility and Sinosure Credit Facility. Our Level 2 derivative assets and liabilities primarily include our interest rate caps, collars, and swaps. Level 3 - Inputs that are unobservable (for example cash flow modeling inputs based on assumptions). ​ 11. Income taxes — ​ Net deferred tax assets are recorded to the extent the Company believes these assets will more likely than not be realized. In making such a determination, all available positive and negative evidence is considered, including future reversals of existing taxable temporary differences, projected future taxable income, tax-planning strategies, and results of recent operations. In the event the Company were to determine that it would be able to realize its deferred income tax assets in the future in excess of their net recorded amount, an adjustment would be made to the deferred tax asset valuation allowance, which would reduce the provision for income taxes in the period such determination is made. ​ Uncertain tax positions are recorded in accordance with ASC 740, Income Taxes, ​ 12. Valuation of equity method investments — ​ 13. Use of estimates ​ 14. Recently adopted accounting standards — Financial Instruments – Credit Losses is deemed uncollectible will be written off in a manner consistent with existing standards. In addition, for guarantees in the scope of ASC 326, entities must measure the expected credit losses arising from the contingent aspect under the CECL model in addition to recognizing the liability for the noncontingent aspect of the guarantee under ASC 460, Guarantees Financial Instruments – Credit Losses ​ In August 2018, the FASB issued ASU 2018-14, Defined Benefit Plans ​ In August 2018, the FASB issued ASU 2018-13, Fair Value Measurement year ended December 31, 2020. ​ On May 20, 2020, the SEC issued a final rule that amends the financial statement requirements for acquisitions and dispositions of businesses. Among other changes, the final rule modifies the significance tests and disclosure requirements for (i) acquired or to be acquired businesses, (ii) real estate operations, (iii) pro forma financial information and (iv) equity method investees. Key amendments in the final rule will (i) change the investment test to use the aggregate worldwide market value of common equity of the registrant when a registrant is evaluating businesses for significance ; and (ii) change the income test to use the lower measure of significance based on (1) income from continuing operations before taxes or (2) revenue. The new rule requires the use of absolute values of five years income instead of zeros for loss years. However, the amendments also limit the use of income averaging to situations in which the revenue test is not applicable (i.e., either the registrant or the acquiree did not have material revenue in each of the two most recently completed fiscal years). Because we do have material revenue in the past two years, we can’t use five year averaging. The final rule is applicable for a registrant’s fiscal year beginning after December 31, 2020 and early application is permitted. The Company adopted this final rule to take advantage of the revenue test in evaluating the significance of our joint ventures accounted for using the equity method. ​ 15. Recently issued accounting standards — Reference Rate Reform which provides relief for companies preparing for discontinuation of interest rates such as LIBOR. A contract modification is eligible to apply the optional relief to account for the modifications as a continuation of the existing contracts without additional analysis and consider embedded features to be clearly and closely related to the host contract without reassessment, if all of the following criteria are met: (i) contract references a rate that will be discontinued; (ii) modified terms directly replace (or have potential to replace) this reference rate; and (iii) changes to any other terms that change (or have potential to change) amount and timing of cash flows must be related to replacement of the reference rate. In addition, this guidance provides relief from certain hedge accounting requirements. Hedge accounting may continue uninterrupted when critical terms change due to reference rate reform. For cash flow hedges, entities can (i) disregard potential discontinuation of a referenced interest rate when assessing whether a hedged forecasted interest payment is probable; (ii) continue hedge accounting upon a change in the hedged risk as long as the hedge is still highly effective; (iii) assess effectiveness of the hedge relationship in ways that essentially disregards a potential mismatch in the variable rate indices between the hedging instrument and the hedged item; and (iv) disregard the requirement that individual hedged transactions must share the same risk exposure for hedges of portfolios of forecasted transactions that reference a rate affected by reference rate reform. Relief provided by this ASU is optional and expires December 31, 2022. In January 2021, the FASB issued ASU 2021-01, Reference Rate Reform

EARNINGS PER COMMON SHARE

EARNINGS PER COMMON SHARE	12 Months Ended
	Dec. 31, 2020
EARNINGS PER COMMON SHARE [Abstract]
EARNINGS PER COMMON SHARE	NOTE 3 — EARNINGS PER COMMON SHARE: ​ Basic earnings per common share is computed by dividing earnings, after the deduction of dividends and undistributed earnings allocated to participating securities, by the weighted average number of common shares outstanding during the period. ​ The computation of diluted earnings per share assumes the issuance of common stock for all potentially dilutive stock options and restricted stock units not classified as participating securities. Participating securities are defined by ASC 260, Earnings Per Share, ​ There were 48,229, 48,014 and 42,449 weighted average shares of unvested restricted common stock shares considered to be participating securities for the years ended December 31, 2020, 2019 and 2018, respectively. Such participating securities are allocated a portion of income, but not losses under the two-class method. As of December 31, 2020, there were 233,833 shares of restricted stock units and 670,624 stock options outstanding considered to be potentially dilutive securities. ​ Reconciliations of the numerator of the basic and diluted earnings per share computations are as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (Dollars in thousands) ​ ​ 2020 ​ ​ 2019 ​ ​ 2018 Net loss allocated to: ​ ​ ​ ​ ​ ​ ​ ​ ​ Common Stockholders ​ $ (5,544) ​ $ (830) ​ $ (88,940) Participating securities ​ ​ 13 ​ ​ — ​ ​ — ​ ​ $ (5,531) ​ $ (830) ​ $ (88,940) ​ There were no dilutive equity awards outstanding for the years ended December 31, 2020, 2019 and 2018. Awards of 962,205, 746,616 and 523,544 for the years ended December 31, 2020, 2019 and 2018, respectively, were not included in the computation of diluted earnings per share because inclusion of these awards would be anti-dilutive.

BUSINESS AND SEGMENT REPORTING

BUSINESS AND SEGMENT REPORTING	12 Months Ended
	Dec. 31, 2020
BUSINESS AND SEGMENT REPORTING [Abstract]
BUSINESS AND SEGMENT REPORTING	NOTE 4 — BUSINESS AND SEGMENT REPORTING: ​ The Company is engaged primarily in the ocean transportation of crude oil and petroleum products in the international market through the ownership and operation of a diversified fleet of vessels. The shipping industry has many distinct market segments based, in large part, on the size and design configuration of vessels required and, in some cases, on the flag of registry. Rates in each market segment are determined by a variety of factors affecting the supply and demand for vessels to move cargoes in the trades for which they are suited. Tankers are not bound to specific ports or schedules and therefore can respond to market opportunities by moving between trades and geographical areas. The Company charters its vessels to commercial shippers and foreign governments and governmental agencies primarily on voyage charters and on time charters. ​ The Company has two reportable segments: Crude Tankers and Product Carriers. The joint ventures with two floating storage and offloading service vessels are included in the Crude Tankers Segment. The joint venture with four LNG Carriers, which was sold in October 2019, was included in Other. Adjusted income/(loss) from vessel operations for segment reporting is defined as income/(loss) from vessel operations before general and administrative expenses, provision for credit losses, ​ ​ Information about the Company’s reportable segments as of and for each of the years in the three-year period ended December 31, 2020 follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Crude ​ Product ​ ​ ​ ​ ​ ​ (Dollars in thousands) ​ Tankers ​ Carriers ​ Other ​ Totals 2020 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Shipping revenues ​ $ 334,765 ​ $ 86,883 ​ $ — ​ $ 421,648 Time charter equivalent revenues ​ ​ 318,588 ​ ​ 83,417 ​ ​ — ​ ​ 402,005 Depreciation and amortization ​ ​ 57,980 ​ ​ 16,269 ​ ​ 94 ​ ​ 74,343 Loss on disposal of vessels and other property, including impairments ​ ​ 44,330 ​ ​ 55,757 ​ ​ — ​ ​ 100,087 Adjusted income/(loss) from vessel operations ​ ​ 144,451 ​ ​ 24,818 ​ ​ (94) ​ ​ 169,175 Equity in income of affiliated companies ​ ​ 4,119 ​ ​ — ​ ​ — ​ ​ 4,119 Investments in and advances to affiliated companies at December 31, 2020 ​ ​ 134,439 ​ ​ 7,485 ​ ​ — ​ ​ 141,924 Adjusted total assets at December 31, 2020 ​ ​ 1,112,342 ​ ​ 253,990 ​ ​ — ​ ​ 1,366,332 Expenditures for vessels and vessel improvements ​ ​ 27,858 ​ ​ 22,191 ​ ​ — ​ ​ 50,049 Payments for drydocking ​ ​ 20,313 ​ ​ 5,329 ​ ​ — ​ ​ 25,642 2019 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Shipping revenues ​ $ 285,356 ​ $ 80,828 ​ $ — ​ $ 366,184 Time charter equivalent revenues ​ ​ 259,517 ​ ​ 80,402 ​ ​ — ​ ​ 339,919 Depreciation and amortization ​ ​ 59,387 ​ ​ 16,152 ​ ​ 114 ​ ​ 75,653 Loss on disposal of vessels and other property ​ ​ 82 ​ ​ 226 ​ ​ — ​ ​ 308 Adjusted income/(loss) from vessel operations ​ ​ 71,344 ​ ​ 12,319 ​ ​ (114) ​ ​ 83,549 Equity in income/(loss) of affiliated companies ​ ​ 19,383 ​ ​ — ​ ​ (8,170) ​ ​ 11,213 Investments in and advances to affiliated companies at December 31, 2019 ​ ​ 143,095 ​ ​ 10,197 ​ ​ — ​ ​ 153,292 Adjusted total assets at December 31, 2019 ​ ​ 1,284,631 ​ ​ 313,063 ​ ​ — ​ ​ 1,597,694 Expenditures for vessels and vessel improvements ​ ​ 33,384 ​ ​ 3,223 ​ ​ — ​ ​ 36,607 Payments for drydocking ​ ​ 16,997 ​ ​ 2,549 ​ ​ — ​ ​ 19,546 2018 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Shipping revenues ​ $ 202,396 ​ $ 67,965 ​ $ — ​ $ 270,361 Time charter equivalent revenues ​ ​ 175,524 ​ ​ 67,576 ​ ​ — ​ ​ 243,100 Depreciation and amortization ​ ​ 54,431 ​ ​ 17,862 ​ ​ 135 ​ ​ 72,428 Loss/(gain) on disposal of vessels and other property, including impairments ​ ​ 22,992 ​ ​ (3,312) ​ ​ — ​ ​ 19,680 Adjusted income/(loss) from vessel operations ​ ​ 2,194 ​ ​ (12,002) ​ ​ 567 ​ ​ (9,241) Equity in income of affiliated companies ​ ​ 19,582 ​ ​ — ​ ​ 9,850 ​ ​ 29,432 Investments in and advances to affiliated companies at December 31, 2018 ​ ​ 143,789 ​ ​ 12,321 ​ ​ 112,212 ​ ​ 268,322 Adjusted total assets at December 31, 2018 ​ ​ 1,285,433 ​ ​ 328,792 ​ ​ 112,212 ​ ​ 1,726,437 Expenditures for vessels and vessel improvements ​ ​ 146,322 ​ ​ 2,624 ​ ​ — ​ ​ 148,946 Payments for drydocking ​ ​ 4,121 ​ ​ 399 ​ ​ — ​ ​ 4,520 ​ Reconciliations of time charter equivalent revenues of the segments to shipping revenues as reported in the consolidated statements of operations follow: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (Dollars in thousands) ​ ​ 2020 ​ ​ 2019 ​ ​ 2018 Time charter equivalent revenues ​ $ 402,005 ​ $ 339,919 ​ $ 243,100 Add: Voyage expenses ​ ​ 19,643 ​ ​ 26,265 ​ ​ 27,261 Shipping revenues ​ $ 421,648 ​ $ 366,184 ​ $ 270,361 ​ Consistent with general practice in the shipping industry, the Company uses time charter equivalent revenues, which represents shipping revenues less voyage expenses, as a measure to compare revenue generated from a voyage charter to revenue generated from a time charter. Time charter equivalent revenues, a non-GAAP measure, provides additional meaningful information in conjunction with shipping revenues, the most directly comparable GAAP measure, because it assists Company management in making decisions regarding the deployment and use of its vessels and in evaluating their financial performance. ​ Reconciliations of adjusted income/(loss) from vessel operations of the segments to income/(loss) before income taxes, as reported in the consolidated statements of operations follow: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (Dollars in thousands) ​ ​ 2020 ​ ​ 2019 ​ ​ 2018 Total adjusted income/(loss) from vessel operations of all segments ​ $ 169,175 ​ $ 83,549 ​ $ (9,241) General and administrative expenses ​ ​ (29,047) ​ ​ (26,798) ​ ​ (24,304) Provision for credit losses, net ​ ​ 71 ​ ​ (1,245) ​ ​ — Third-party debt modification fees ​ ​ (232) ​ ​ (30) ​ ​ (1,306) Loss on disposal of vessels and other property, including impairments ​ ​ (100,087) ​ ​ (308) ​ ​ (19,680) Consolidated income/(loss) from vessel operations ​ ​ 39,880 ​ ​ 55,168 ​ ​ (54,531) Equity in income of affiliated companies ​ ​ 4,119 ​ ​ 11,213 ​ ​ 29,432 Other expense ​ ​ (12,817) ​ ​ (943) ​ ​ (3,715) Interest expense ​ ​ (36,712) ​ ​ (66,267) ​ ​ (60,231) Income/(loss) before income taxes ​ $ (5,530) ​ $ (829) ​ $ (89,045) ​ Reconciliations of adjusted total assets of the segments to amounts included in the consolidated balance sheets follow: ​ ​ ​ ​ ​ ​ ​ ​ (Dollars in thousands) ​ December 31, 2020 ​ December 31, 2019 Adjusted total assets of all segments ​ $ 1,366,332 ​ $ 1,597,694 Corporate unrestricted cash and cash equivalents ​ ​ 199,390 ​ ​ 89,671 Restricted cash ​ ​ 16,287 ​ ​ 60,572 Other unallocated amounts ​ ​ 4,530 ​ ​ 5,564 Consolidated total assets ​ $ 1,586,539 ​ $ 1,753,501 ​ Certain additional information about the Company’s operations for each of the years in the three year period ended December 31, 2020 follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Crude ​ Product ​ ​ ​ ​ ​ ​ (Dollars in thousands) ​ Tankers ​ Carriers ​ ​ Other ​ Consolidated Total vessels, deferred drydock and other property at December 31, 2020 ​ $ 919,974 ​ $ 224,507 ​ $ 67 ​ $ 1,144,548 Total vessels, deferred drydock and other property at December 31, 2019 ​ ​ 1,051,848 ​ ​ 263,651 ​ ​ 142 ​ ​ 1,315,641 Total vessels, deferred drydock and other property at December 31, 2018 ​ ​ 1,057,994 ​ ​ 289,317 ​ ​ 257 ​ ​ 1,347,568 ​

VESSELS, DEFERRED DRYDOCK AND O

VESSELS, DEFERRED DRYDOCK AND OTHER PROPERTY	12 Months Ended
	Dec. 31, 2020
VESSELS, DEFERRED DRYDOCK AND OTHER PROPERTY [Abstract]
VESSELS, DEFERRED DRYDOCK AND OTHER PROPERTY	NOTE 5 — VESSELS, DEFERRED DRYDOCK AND OTHER PROPERTY: ​ Vessels and other property, excluding vessel held for sale, consist of the following: ​ ​ ​ ​ ​ ​ ​ ​ (Dollars in thousands) ​ December 31, 2020 ​ December 31, 2019 Vessels, at cost ​ $ 1,287,688 ​ $ 1,650,670 Accumulated depreciation ​ ​ (182,148) ​ ​ (361,088) Vessels, net ​ ​ 1,105,540 ​ ​ 1,289,582 Other property, at cost ​ ​ 6,610 ​ ​ 6,714 Accumulated depreciation and amortization ​ ​ (3,936) ​ ​ (3,780) Other property, net ​ ​ 2,674 ​ ​ 2,934 Total Vessels and other property ​ $ 1,108,214 ​ $ 1,292,516 ​ ​ Twenty of the Company’s owned vessels are pledged as collateral under either the Core Term Loan Facility or Sinosure Credit Facility (see Note 8, “Debt”). The aggregate carrying value of the 14 vessels pledged as collateral under the Core Term Loan Facility, and the six vessels pledged as collateral under Sinosure Credit Facility was $551.3 million and $429.5 million, respectively. A breakdown of the carrying value of the Company’s owned vessels by reportable segment and fleet as of December 31, 2020 and 2019 follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net ​ ​ Average ​ ​ Number of ​ ​ ​ ​ ​ Accumulated ​ Carrying ​ ​ Vessel Age ​ ​ Owned As of December 31, 2020 (Dollars in thousands) ​ Cost ​ Depreciation ​ Value ​ ​ (by dwt) ​ ​ Vessels Crude Tankers ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ VLCC ​ $ 839,542 ​ $ (131,862) ​ $ 707,680 ​ ​ 7.9 ​ ​ 11 Suezmax ​ ​ 117,338 ​ ​ (14,099) ​ ​ 103,239 ​ ​ 3.4 ​ ​ 2 Aframax (1) ​ ​ 32,395 ​ ​ (1,378) ​ ​ 31,017 ​ ​ 7.5 ​ ​ 1 Panamax ​ ​ 57,992 ​ ​ (8,111) ​ ​ 49,881 ​ ​ 18.2 ​ ​ 7 Total Crude Tankers ​ ​ 1,047,267 ​ ​ (155,450) ​ ​ 891,817 (2) ​ 8.8 ​ ​ 21 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Product Carriers ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ LR2 ​ ​ 73,710 ​ ​ (17,419) ​ ​ 56,291 ​ ​ 6.4 ​ ​ 1 LR1 ​ ​ 96,838 ​ ​ (9,279) ​ ​ 87,559 ​ ​ 11.9 ​ ​ 5 MR ​ ​ 69,873 ​ ​ — ​ ​ 69,873 ​ ​ 10.0 ​ ​ 4 Total Product Carriers ​ ​ 240,421 ​ ​ (26,698) ​ ​ 213,723 (3) ​ 10.5 ​ ​ 10 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fleet Total ​ $ 1,287,688 ​ $ (182,148) ​ $ 1,105,540 ​ ​ 9.0 ​ ​ 31 (1) Net carrying value includes assets capitalized on two bareboat chartered-in Aframaxes. (2) Includes 10 VLCCs and one Panamax with an aggregate carrying value of $695.3 million, which the Company believes exceeds their aggregate market values (estimated by taking an average of two third party vessel appraisals) of approximately $584.0 million by $111.3 million. (3) Includes one LR2 and three LR1s with an aggregate carrying value of $106.3 million, which the Company believes exceeds their aggregate market values (estimated by taking an average of two third party vessel appraisals) of approximately $75.6 million by $30.7 million. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net ​ ​ Average ​ ​ Number of ​ ​ ​ ​ ​ Accumulated ​ Carrying ​ ​ Vessel Age ​ ​ Owned As of December 31, 2019 (Dollars in thousands) ​ Cost ​ Depreciation ​ Value ​ ​ (by dwt) ​ ​ Vessels Crude Tankers ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ VLCC ​ $ 1,028,760 ​ $ (236,217) ​ $ 792,543 ​ ​ 8.6 ​ ​ 13 Suezmax ​ ​ 117,338 ​ ​ (10,007) ​ ​ 107,331 ​ ​ 2.4 ​ ​ 2 Aframax ​ ​ 96,038 ​ ​ (19,659) ​ ​ 76,379 ​ ​ 14.1 ​ ​ 3 Panamax ​ ​ 59,181 ​ ​ (5,223) ​ ​ 53,958 ​ ​ 17.2 ​ ​ 7 Total Crude Tankers ​ ​ 1,301,317 ​ ​ (271,106) ​ ​ 1,030,211 ​ ​ 9.4 ​ ​ 25 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Product Carriers ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ LR2 ​ ​ 73,681 ​ ​ (14,714) ​ ​ 58,967 ​ ​ 5.4 ​ ​ 1 LR1 ​ ​ 108,251 ​ ​ (22,420) ​ ​ 85,831 ​ ​ 11.0 ​ ​ 4 MR ​ ​ 167,421 ​ ​ (52,848) ​ ​ 114,573 ​ ​ 9.0 ​ ​ 4 Total Product Carriers ​ ​ 349,353 ​ ​ (89,982) ​ ​ 259,371 ​ ​ 9.3 ​ ​ 9 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fleet Total ​ $ 1,650,670 ​ $ (361,088) ​ $ 1,289,582 ​ ​ 9.4 ​ ​ 34 ​ ​ Vessel activity for the three years ended December 31, 2020 is summarized as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (Dollars in thousands) ​ Vessel Cost ​ Accumulated Depreciation ​ Net Book Value Balance at January 1, 2018 ​ $ 1,404,360 ​ $ (302,087) ​ $ 1,102,273 Purchases and vessel additions ​ ​ 459,608 ​ ​ — ​ ​ ​ Disposals ​ ​ (176,300) ​ ​ 16,097 ​ ​ ​ Depreciation ​ ​ — ​ ​ (56,711) ​ ​ ​ Impairment ​ ​ (58,021) ​ ​ 40,816 ​ ​ ​ Balance at December 31, 2018 ​ ​ 1,629,647 ​ ​ (301,885) ​ ​ 1,327,762 Purchases and vessel additions ​ ​ 38,138 ​ ​ — ​ ​ ​ Disposals ​ ​ (17,115) ​ ​ 1,105 ​ ​ ​ Depreciation ​ ​ — ​ ​ (60,308) ​ ​ ​ Balance at December 31, 2019 ​ ​ 1,650,670 ​ ​ (361,088) ​ ​ 1,289,582 Purchases and vessel additions ​ ​ 48,436 ​ ​ — ​ ​ ​ Disposals ​ ​ (70,353) ​ ​ 2,763 ​ ​ ​ Depreciation ​ ​ — ​ ​ (61,866) ​ ​ ​ Impairment ​ ​ (341,065) ​ ​ 238,043 ​ ​ ​ Balance at December 31, 2020 ​ $ 1,287,688 ​ $ (182,148) ​ $ 1,105,540 ​ The total of purchases and vessel additions will differ from expenditures for vessels as shown in the consolidated statements of cash flows because of the timing of when payments were made. ​ Vessel Impairments ​ During the year ended December 31, 2020, the Company gave consideration on a quarterly basis as to whether events or changes in circumstances had occurred since December 31, 2019 that could indicate that the carrying amounts of the vessels in the Company’s fleet may not be recoverable. Factors considered included declines in valuations for vessels of certain sizes and ages, any negative changes in forecasted near term charter rates, and an increase in the likelihood that the Company will sell certain of its vessels before the end of their estimated useful lives in conjunction with the Company’s fleet renewal program. In addition, the economic impacts of the novel coronavirus (COVID-19) did not have immediate material negative impacts on the markets for our vessels and there was a very strong rate environment for our fleets for fixtures concluded during the latter portion of the first quarter of 2020 into the second quarter of 2020, which was principally due to temporary increases in oil production and a growth in demand for floating storage. Commencing from the latter part of the second quarter of 2020, principally as the result of the impact of the COVID-19 pandemic, oil production declined and consequently so did the need for floating storage. This development negatively impacted the demand for oil tankers during the second half of 2020. The extent to which the current COVID-19 related market conditions will continue to negatively impact the tanker rate environment will depend on the extent to which oil demand is met from excess crude inventories that were built up during the period of oil demand destruction, the timing and magnitude of oil demand recoveries in the various parts of the world and the levels of oil production during such periods September 30, 2020; and (iii) ​ In developing estimates of undiscounted future cash flows for performing Step 1 of the impairment tests as of June 30, 2020, the Company utilized weighted probabilities assigned to possible outcomes for each of the two vessels for which impairment triggering events were determined to exist. As the Company was considering selling the two VLCCs as a part of its fleet renewal program, 25% probabilities were assigned to the possibility that the two VLCCs would be sold prior to the end of their respective useful lives. The carrying value for one of the two VLCCs was estimated to be unrecoverable in the Step 1 test. In estimating the fair value of the vessel for the purposes of Step 2 of the impairment test, the Company developed fair value estimates that utilized a market approach which considered an average of two vessel appraisals obtained from third-party valuation specialists. Based on the tests performed, an impairment charge totaling $5.5 million was recorded on the 2002-built VLCC to write-down its carrying value to its estimated fair value at June 30, 2020. ​ Interest and activity in the sale and purchase market for older VLCCs increased subsequent to June 30, 2020 and the Company entered into memoranda of agreements for the sale of the two VLCCs in early October 2020. Accordingly, a 100% probability was attributed to the two VLCCs being sold before the end of their useful lives in developing estimates of undiscounted future cash flows for performing Step 1 of the impairment tests as of September 30, 2020. The carrying values for the two VLCCs were estimated to be unrecoverable in the Step 1 test. In estimating the fair values of the vessels for the purposes of Step 2 of the impairment test, the Company considered the market approach by using the sales prices per the memoranda of agreements. Based on the tests performed, an impairment charge totaling $11.7 million was recorded on the two VLCCs to write-down their carrying values to their estimated fair values at September 30, 2020. ​ In developing estimates of undiscounted future cash flows for performing Step 1 of the impairment tests as of December 31, 2020, the Company utilized weighted probabilities assigned to possible outcomes for the vessels that the Company was considering to sell or recycle before the end of their respective useful lives. The Company made assumptions about future performance, with significant assumptions being related to charter rates, operating expenses, utilization, drydocking and capital expenditure requirements, residual value and the estimated remaining useful lives of the vessels. These assumptions are based on historical trends as well as future expectations. The estimated daily time charter equivalent rates used for unfixed days were based on a combination of (i) rates as forecasted by third party analysts, and (ii) the trailing 12-year historical average rates, based on monthly average rates published by a third party maritime research service. Management used the published 12-year historical average rates in its assumptions because it is management’s belief that the 12-year period captures an even distribution of strong and weak charter rate periods, which results in the use of an average mid-cycle rate that is in line with management’s forecast of a return to mid-cycle charter rate levels in the medium term. Recognizing that the transportation of crude oil and petroleum products is cyclical and subject to significant volatility based on factors beyond the Company’s control, management believes the use of estimates based on the combination of internally forecasted rates and 12-year historical average rates calculated as of the reporting date to be reasonable. ​ Estimated outflows for operating expenses and capital expenditures and drydocking requirements are based on historical and budgeted costs and are adjusted for assumed inflation. Utilization was based on historical levels achieved and estimates of a residual value for recyclings are based upon published 12-year historical data or the pattern of scrap steel prices used in management’s evaluation of salvage value for purposes of recording depreciation. ​ In estimating the fair value of the vessel for the purposes of Step 2 of the impairment test, the Company developed fair value estimates that utilized a market approach which considered an average of two vessel appraisals obtained from third-party valuation specialists. Based on the tests performed, the Company recorded impairment charges totaling $85.9 million on its one remaining older VLCC, one Aframax, two LR1s, and its four MRs to write-down their carrying values to their estimated fair values at December 31, 2020. ​ The Company gave consideration as to whether events or changes in circumstances had occurred since December 31, 2018 that could indicate that the carrying amounts of the vessels in the Company’s fleet may not be recoverable as of December 31, 2019 and concluded that ​ During the year ended December 31, 2018, the Company gave consideration on a quarterly basis as to whether events or changes in circumstances had occurred since December 31, 2017 that could indicate that the carrying amounts of the vessels in the Company’s fleet may not be recoverable. Factors considered included declines in valuations during 2018 for vessels of certain sizes and ages, any negative changes in forecasted near term charter rates, and an increase in the likelihood that the Company will sell certain of its vessels before the end of their estimated useful lives in conjunction with the Company’s fleet renewal program. The Company concluded that the increased likelihood of disposal prior to the end of their respective useful lives constituted impairment triggering events for one Panamax and two Aframaxes that were being actively marketed for sale as of June 30, 2018; one VLCC that was held-for-sale as of September 30, 2018; and one MR that had an increased likelihood of disposal prior to the end of its useful life as of December 31, 2018. ​ In developing estimates of undiscounted future cash flows for performing Step 1 of the impairment tests as of June 30, 2018, the Company utilized weighted probabilities assigned to possible outcomes for each of the three vessels for which impairment trigger events were determined to exist. The Company entered into a memorandum of agreement for the sale of the Panamax vessel in early July 2018. Accordingly, a 100% probability was attributed to the vessel being sold before the end of its useful life. As the Company was considering selling the other two vessels as a part of its fleet renewal program, 50% probabilities were assigned to the possibility that the two Aframax vessels would be sold prior to the end of their respective useful lives. In estimating the fair value of the vessels for the purposes of Step 2 of the impairment tests, the Company considered the market approach by using the sales price per the memorandum of agreement. Based on the tests performed, the sum of the undiscounted cash flows for each of the two Aframax vessels was more than its carrying value as of June 30, 2018 and the sum of the undiscounted cash flows for the Panamax vessel was less than its carrying value as of June 30, 2018. Accordingly, an impairment charge totaling $0.9 million was recorded for the Panamax vessel to write-down its carrying value to its estimated fair value at June 30, 2018. ​ Held-for-sale impairment charges aggregating $16.4 million were recorded during the third quarter of 2018 including (i) a charge of $14.2 million to write the value of the VLCC held-for-sale at September 30, 2018 down to its estimated fair value; (ii) a charge of $0.4 million for estimated costs to sell the vessel; and (iii) a charge of $1.8 million for the write-off of other assets associated with the operations of the vessel. The amount of the charge to write down the vessel to its fair value was determined using the market approach by utilizing the sales price per the memorandum of agreement. ​ In developing estimates of undiscounted future cash flows for performing Step 1 of the impairment test as of December 31, 2018, the Company utilized weighted probabilities assigned to possible outcomes for the MR for which an impairment triggering event was determined to exist. As the Company was considering selling the MR as a part of its fleet renewal program, a 50% probability was assigned to the possibility that the vessel would be sold prior to the end of its useful life. In estimating the fair value of the vessel for the purposes of Step 2 of the impairment test, the Company considered the market approach by utilizing a combination of third party appraisals and recently executed vessel sale transactions. Based on the tests performed, the sum of the undiscounted cash flows for the vessel was less than its carrying value as of December 31, 2018. Accordingly, an impairment charge totaling $1.7 million was recorded to write-down the vessel’s carrying value to its estimated fair value at December 31, 2018. ​ Vessel Acquisitions and Deliveries ​ In December 2019, the Company entered into a memorandum of agreement for the acquisition of a 2009-built LR1 for a purchase price of $18.8 million, which was delivered during the first quarter of 2020. ​ On June 14, 2018, the Company completed its acquisition of six 300,000 DWT VLCCs including one 2015-built and five 2016-built. The Company purchased the outstanding shares of Gener8 Maritime Subsidiary VII, Inc., which has been renamed Seaways Subsidiary VII, Inc., a corporation incorporated under the laws of the Marshall Islands and the sole owner of six limited liability companies each of which holds title to a VLCC tanker. The acquisition was completed pursuant to the terms of the Stock Purchase and Sale Agreement dated as of April 18, 2018, by and among Seaways Holding Corporation, a corporation incorporated under the laws of the Marshall Islands and a wholly-owned subsidiary of the Company, Euronav NV (“Euronav”), a corporation incorporated and existing under the laws of the Kingdom of Belgium, and Euronav MI II Inc. (as successor to Euronav MI Inc.), a corporation incorporated under the laws of the Marshall Islands and a wholly-owned subsidiary of Euronav. In accordance with ASC 2017-01, Business Combinations (Topic 805), this acquisition did not constitute the acquisition of a business, and therefore was accounted for as an asset acquisition. The purchase price for the acquisition was $434.0 million, inclusive of assumed debt secured by the six vessels (see Note 8, “Debt”). On June 14, 2018, the Company paid to Euronav cash consideration of approximately $120.0 million, with the difference reflecting assumed debt and accrued interest thereon through the acquisition date. An additional $20.9 million was paid to Euronav in October 2018 for the other assets and liabilities of Gener8 Maritime Subsidiary VII, Inc. that were acquired in the transaction. ​ Disposal/Sales of Vessel and Other Property ​ During 2020, the Company recognized a net aggregate gain of $4.5 million on disposal of a 2002-built Aframax, a 2001-built Aframax, a 2003-built VLCC, and a 2002-built VLCC. The Company also recognized an aggregate loss of approximately $1.6 million during 2020 related to the termination of the purchase and installation contracts for ballast water treatment systems on five of the Company’s Panamaxes. The contracts were terminated as a result of the Company being granted an extension by the United States Coast Guard on the requirement to install ballast water treatment systems on these Panamaxes until 2022. ​ During 2019, the Company recognized a net aggregate loss of $0.3 million on disposal of two 2004-built MRs. ​ During 2018, the Company recognized a net aggregate gain on disposal of vessels and other property of $0.6 million, primarily relating to (i) the sale of a 2002-built MR which was held-for-sale as of December 31, 2017; (ii) the sale of three 2004-built MRs, a 1998-built MR, a 2000-built VLCC, a 2001-built VLCC, two 2001-built Aframaxes, and a 2002-built Panamax; (iii) the sale and leaseback of two 2009-built Aframaxes, and (iv) the sale of a 2003-built ULCC in conjunction with the acquisition of the six VLCCs discussed above. ​ Drydocking activity for the three years ended December 31, 2020 is summarized as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (Dollars in thousands) ​ 2020 ​ 2019 ​ 2018 Balance at January 1 ​ $ 23,125 ​ $ 16,773 ​ $ 30,528 Additions ​ ​ 27,835 ​ ​ 21,086 ​ ​ 5,616 Sub-total ​ ​ 50,960 ​ ​ 37,859 ​ ​ 36,144 Drydock amortization ​ ​ (11,780) ​ ​ (14,685) ​ ​ (15,084) Amount charged to loss on disposal of vessels ​ ​ (2,846) ​ ​ (49) ​ ​ (4,287) Balance at December 31 ​ $ 36,334 ​ $ 23,125 ​ $ 16,773 ​ The total additions above will differ from payments for drydocking as shown in the consolidated statements of cash flows because of the timing of when payments were made.

EQUITY METHOD INVESTMENTS

EQUITY METHOD INVESTMENTS	12 Months Ended
	Dec. 31, 2020
EQUITY METHOD INVESTMENTS [Abstract]
EQUITY METHOD INVESTMENTS	NOTE 6 — EQUITY METHOD INVESTMENTS: ​ Investments in affiliated companies include joint ventures accounted for using the equity method. ​ FSO Joint Venture ​ As of December 31, 2020, the Company had a 50% interest in two joint ventures with Euronav NV. The two joint ventures converted two ULCCs to Floating Storage and Offloading Service vessels (collectively the “FSO Joint Venture”). In May 2017, the FSO Joint Venture signed two five-year service contracts with North Oil Company (“NOC”), the operator of the Al Shaheen oil field, off the coast of Qatar, relating to the two FSO service vessels. The shareholders of NOC are Qatar Petroleum Oil & Gas Limited and Total E&P Golfe Limited. In October 2020, the FSO Joint Venture signed a 10-year extension on each of the existing service contracts with NOC relating to the two FSO service vessels. Such extensions shall commence in direct continuation of the existing contracts, which were originally scheduled to expire during the third quarter of 2022. ​ The FSO Joint Venture financed the purchase of the two ULCCs from each of Euronav NV and INSW and their conversion costs through partner loans and a long-term bank financing which was paid off in July 2017. On March 29, 2018, the FSO Joint Venture executed an agreement on a $220 million secured credit facility (the “FSO Loan Agreement”). The FSO Loan Agreement is among TI Africa and TI Asia, as joint and several borrowers, ABN AMRO Bank N.V. and ING Belgium SA/NV, as Lenders, Mandated Lead Arrangers and Swap Banks, and ING Bank N.V., as Agent and as Security Trustee. The FSO Loan Agreement provides for (i) a term loan of $110 million (the “FSO Term Loan”), which is repayable in scheduled quarterly installments over the course of the two service contracts in effect for the FSO Asia and FSO Africa with North Oil Company, maturing in July 2022 and September 2022, respectively; and (ii) a revolving credit facility of $110 million (the “FSO Revolver”), which revolving credit commitment reduces quarterly over the course of the foregoing two service contracts. INSW provided a guarantee for the $110 million FSO Term Loan portion of the facility and Euronav provided a guarantee for the $110 million FSO Revolver. The FSO Joint Venture drew down and distributed the entire $110 million of proceeds of the FSO Term Loan on April 26, 2018 to INSW, which used the proceeds for general corporate purposes, including to fund partially the purchase of six VLCCs in June 2018 (See Note 5, “Vessels, Deferred Drydock and Other Property”). The FSO Joint Venture also borrowed the entire $110 million available under the FSO Revolver and distributed the proceeds on April 26, 2018 to Euronav. The FSO Term Loan and the FSO Revolver are secured by, among other things, a first preferred vessel mortgage on the FSO Africa and FSO Asia, an assignment of the service contracts for the FSO Africa and FSO Asia and the aforementioned guarantees of the FSO Term Loan by INSW and the guarantee of the FSO Revolver by Euronav. The FSO Loan Agreement has a financial covenant that the Debt Service Cover Ratio (as defined in the agreement) shall be equal to or greater than 1.10 to 1.00. Approximately $45.2 million and $69.6 million was outstanding under each of the FSO Term Loan and the FSO Revolver, respectively, as of December 31, 2020 and 2019, respectively. The FSO Joint Venture has agreed to pay a commitment fee (“FSO Commitment Fee”) of 0.7% on any undrawn amount under the FSO Revolver. INSW has agreed to pay Euronav through July 2021 for the FSO Asia and September 2021 for the FSO Africa, an amount equal to the first 0.3% of the 0.7% FSO Commitment Fee and, to the extent the FSO Revolver is fully drawn, to pay Euronav an amount equal to the first 0.3% of the amount of loan interest payable under the FSO Revolver. ​ Interest payable on the FSO Term Loan and on the FSO Revolver is based on three month, six month or twelve month LIBOR, as selected by the FSO Joint Venture, plus a 2.00% margin. The FSO Joint Venture has entered into swap transactions, which fix the interest rate on the FSO Loan Agreement at a blended rate of approximately 4.858% per annum, effective as of June 29, 2018. The interest rate swap covers a notional amount of $90.4 million and $139.2 million as of December 31, 2020 and 2019, respectively. As of December 31, 2020 and 2019, the FSO Joint Venture had a liability of $2.4 million, respectively, for the fair value of the swaps associated with the FSO Joint Venture. The Company’s share of the effective portion of such amounts, aggregating a loss of $1.2 million at December 31, 2020 and 2019, respectively, is included in accumulated other comprehensive loss in the accompanying consolidated balance sheets. ​ The FSO Joint Venture is an obligor pursuant to a guarantee facility agreement dated as of July 14, 2017, by and among, the FSO Joint Venture, ING Belgium NV/SA, as issuing bank, and Euronav and INSW, as guarantors (the ‘‘Guarantee Facility’’). INSW severally guarantees the obligations of the FSO Joint Venture pursuant to the Guarantee Facility. The Guarantee Facility will expire at the commencement of the 10-year INSW’s guarantee of the FSO Term Loan has financial covenants that provide (i) INSW’s Liquid Assets shall not be less than the higher of $50 million and 5% of Total Indebtedness of INSW, (ii) INSW shall have Cash of at least $30 million and (iii) INSW is in compliance with the Loan to Value Test (as such capitalized terms are defined in the Company guarantee). As of December 31, 2020 the maximum aggregate potential amount of future principal payments (undiscounted) relating to the FSO Joint Venture’s secured bank debt and interest rate swap obligations that INSW could be required to make was $46.4 million, and the carrying value of the Company’s guaranty of such FSO Joint Venture obligations in the accompanying consolidated balance sheet as of December 31, 2020 was $44 thousand. ​ LNG Joint Venture In November 2004, the Company formed a joint venture with Qatar Gas Transport Company Limited (Nakilat) (“QGTC”) whereby companies in which the Company held a 49.9% interest ordered four 216,200 cbm LNG Carriers. Upon delivery in late 2007 and early 2008, these vessels commenced 25-year ​ On October 7, 2019, the Company sold its 49.9% ownership interest in the LNG Joint Venture to Nakilat pursuant to a share purchase agreement. The purchase price for the transaction was $123.0 million, excluding fees and expenses. The share purchase agreement contained specified representations, warranties, covenants and indemnification provisions of the parties customary for transactions of this type. In addition, in connection with the transaction, various other agreements governing the LNG Joint Venture and the LNG Joint Venture’s relationships with its counterparties were also amended to reflect the change in ownership and related matters. The Company recorded a cash gain on the sale of $3.0 million and reclassified the Company’s share of the unrealized losses associated with the interest rate swaps held by the LNG Joint Venture of $21.6 million into earnings from accumulated other comprehensive loss. ​ Impairment of Equity Method Investments ​ Management gave consideration as to whether events or changes in circumstances had occurred since December 31, 2017, 2018, and 2019 respectively, that could indicate that the carrying amounts of its investments in the FSO Joint Venture and LNG Joint Venture were not recoverable as of December 31, 2018, 2019, and 2020, respectively. Management concluded that no such events or changes in circumstances had occurred during the years ended December 31, 2018, 2019 and 2020. ​ Financial Information of Significant Equity Method Investments ​ Investments in and advances to affiliated companies as reflected in the accompanying consolidated balance sheet as of December 31, 2020 consisted of: FSO Joint Venture of $128.8 million and Other of $13.1 million (which primarily relates to working capital deposits that the Company maintains for commercial pools in which it participates). ​ ​ Financial information for the equity method investees that were significant for the three years ended December 31, 2020, including the results of the LNG Joint Venture prior to the sale on October 7, 2019, adjusted for basis and accounting policy differences, is as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (Dollars in thousands) ​ 2020 ​ 2019 ​ 2018 Shipping revenues ​ $ 105,053 ​ $ 193,446 ​ $ 209,571 Ship operating expenses ​ ​ (58,858) ​ ​ (103,499) ​ ​ (112,541) Income from vessel operations ​ ​ 46,195 ​ ​ 89,947 ​ ​ 97,030 Other income ​ ​ 22 ​ ​ 1,459 ​ ​ 1,494 Interest expense ​ ​ (6,571) ​ ​ (32,752) ​ ​ (40,676) Income tax provision ​ ​ (36,404) ​ ​ (3,399) ​ ​ (3,433) Net income ​ $ 3,242 ​ $ 55,255 ​ $ 54,415 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Percentage of ownership in equity investees ​ ​ 50.0% ​ ​ 49.9% - 50.0% ​ ​ 49.9% - 50.0% Equity in income of affiliated companies, before consolidating and reconciling adjustments ​ $ 1,621 ​ $ 27,606 ​ $ 27,187 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Gain on sale of investments in affiliated companies ​ ​ — ​ ​ 3,033 ​ ​ — Release other comprehensive loss upon sale of investment in affiliated companies ​ ​ — ​ ​ (21,615) ​ ​ — Amortization of deferred gain on 2009 sale of TI Africa to FSO Joint Venture ​ ​ 2,385 ​ ​ 2,395 ​ ​ 2,395 Amortization of interest capitalized during construction of LNG vessels ​ ​ — ​ ​ (320) ​ ​ (419) Other ​ ​ 113 ​ ​ 114 ​ ​ 269 Equity in income of affiliated companies ​ $ 4,119 ​ $ 11,213 ​ $ 29,432 ​ The increase in the income tax provision in the above table principally reflects a $32.8 million noncash deferred tax provision recorded by the FSO Joint Venture in the fourth quarter of 2020, which was related to the execution of 10-year ​ The tables below present the financial position for the equity method investees and a reconciliation of the Company’s share of the joint ventures’ total equity to the investments in and advances to affiliates line on the consolidated balance sheets as of December 31, 2020 and 2019: ​ ​ ​ ​ ​ ​ ​ ​ (Dollars in thousands) ​ December 31, 2020 ​ December 31, 2019 Current assets ​ $ 20,154 ​ $ 20,808 Vessels, net ​ ​ 490,093 ​ ​ 523,802 Total assets ​ $ 510,247 ​ $ 544,610 ​ ​ ​ ​ ​ ​ ​ Current liabilities ​ $ 59,567 ​ $ 53,774 Long-term debt and other non-current liabilities ​ ​ 111,263 ​ ​ 143,673 Equity ​ ​ 339,417 ​ ​ 347,163 Total liabilities and equity ​ $ 510,247 ​ $ 544,610 ​ ​ ​ ​ ​ ​ ​ Percentage of ownership in equity investees ​ ​ 50.0% ​ ​ 50.0% INSW share of affiliate's equity, before consolidating and reconciling adjustments ​ $ 169,708 ​ $ 173,581 ​ ​ ​ ​ ​ ​ ​ 2016 impairment of equity method investments in FSO Joint Venture ​ ​ (30,475) ​ ​ (30,475) Advances from shareholders of FSO Joint Venture (1) ​ ​ 16,665 ​ ​ 23,216 Unamortized deferred gain on 2009 sale of TI Africa to FSO Joint Venture, net ​ ​ (27,156) ​ ​ (29,503) INSW guarantee for FSO Term Loan ​ ​ 44 ​ ​ 264 Other (2) ​ ​ 13,138 ​ ​ 16,209 Investments in and advances to affiliated companies ​ $ 141,924 ​ $ 153,292 (1) Such advances are unsecured, interest free and not repayable within one year. (2) Primarily relates to working capital deposits that the Company maintains with the commercial pools in which it participates. ​ See Note 9, “Fair Value of Financial Instruments, Derivatives and Fair Value Disclosures,” and Note 13, “Accumulated Other Comprehensive Loss,” for additional disclosures relating to the FSO and LNG joint venture interest rate swap agreements.

VARIABLE INTEREST ENTITIES (VIE

VARIABLE INTEREST ENTITIES (VIEs)	12 Months Ended
	Dec. 31, 2020
VARIABLE INTEREST ENTITIES (VIEs) [Abstract]
VARIABLE INTEREST ENTITIES (VIEs)	NOTE 7 —VARIABLE INTEREST ENTITIES (“VIEs”): ​ At December 31, 2020, the Company participates in five commercial pools and two joint ventures. Commercial pools operate a large number of vessels as an integrated transportation system, which offers customers greater flexibility and a higher level of service while achieving scheduling efficiencies. Participants in the commercial pools contribute one or more vessels and generally provide an initial contribution towards the working capital of the pool at the time they enter their vessels. The pools finance their operations primarily through the earnings that they generate. ​ INSW enters into joint ventures to take advantage of commercial opportunities. In each joint venture, INSW has the same relative rights and obligations and financial risks and rewards as its partners. INSW evaluated all seven arrangements to determine if they were variable interest entities (“VIEs”). INSW determined that one of the pools and the two joint ventures met the criteria of a VIE and, therefore, INSW reviewed its participation in these VIEs to determine if it was the primary beneficiary of any of them. ​ INSW reviewed the legal documents that govern the creation and management of the VIEs described above and also analyzed its involvement to determine if INSW was a primary beneficiary in any of these VIEs. A VIE for which INSW is determined to be the primary beneficiary is required to be consolidated in its financial statements. ​ The formation agreements for the commercial pool state that the board of the pool has decision making power over their significant decisions. In addition, all such decisions must be approved unanimously by the board. Since INSW shares power to make all significant economic decisions that affect the pool and does not control a majority of the board, INSW is not considered a primary beneficiary of the pool. ​ The two FSO joint ventures described in Note 6, “Equity Method Investments,” were determined to be VIEs. The formation agreements of the joint ventures state that all significant decisions must be approved by the majority of the board. As a result, INSW shares power to make all significant economic decisions that affect this joint venture and does not control a majority of the board and is not considered a primary beneficiary. Accordingly, INSW accounts for these investments under the equity method of accounting. ​ The FSO joint ventures’ formation agreements require INSW and its joint venture partner to provide financial support as needed. INSW has provided and will continue to provide such support as described in Note 6, “Equity Method Investments.” ​ The following table presents the carrying amounts of assets and liabilities in the consolidated balance sheets related to the VIEs described above as of December 31, 2020 and 2019: ​ ​ ​ ​ ​ ​ ​ ​ (Dollars in thousands) ​ 2020 ​ 2019 Investments in Affiliated Companies ​ $ 132,902 ​ $ 140,915 ​ In accordance with accounting guidance, the Company evaluated its maximum exposure to loss related to these VIEs by assuming a complete loss of the Company’s investment in these VIEs and the Company’s potential obligations under its guarantee of the FSO Term Loan and associated interest rate swap. The table below compares the Company’s liability in the consolidated balance sheet to the maximum exposure to loss at December 31, 2020: ​ ​ ​ ​ ​ ​ ​ ​ (Dollars in thousands) ​ ​ Consolidated Balance Sheet ​ ​ Maximum Exposure to Loss Other Liabilities ​ $ 44 ​ $ 179,291 ​ In addition, as of December 31, 2020, the Company had approximately $6.7 million of trade receivables from the pool that was determined to be a VIE. These trade receivables, which are included in voyage receivables in the accompanying consolidated balance sheet, have been excluded from the above tables and the calculation of INSW’s maximum exposure to loss. The Company does not record the maximum exposure to loss as a liability because it does not believe that such a loss is probable of occurring as of December 31, 2020.

DEBT

DEBT	12 Months Ended
	Dec. 31, 2020
DEBT [Abstract]
DEBT	NOTE 8 —DEBT: Debt consists of the following: ​ ​ ​ ​ ​ ​ ​ ​ (Dollars in thousands) ​ December 31, 2020 ​ December 31, 2019 Core Term Loan Facility, due 2025, net of unamortized deferred finance costs of $4,145 ​ $ 267,427 ​ $ — Sinosure Credit Facility, due 2027-2028, net of unamortized deferred finance costs of $1,884 and $2,262 ​ ​ 244,243 ​ ​ 267,443 8.5% Senior Notes, due 2023, net of unamortized deferred finance costs of $855 and $1,142 ​ ​ 24,145 ​ ​ 23,858 2017 Term Loan Facility, due 2022, net of unamortized discount and deferred finance costs of $11,211 ​ ​ — ​ ​ 320,309 ABN Term Loan Facility, due 2023, net of unamortized deferred finance costs of $610 ​ ​ — ​ ​ 22,638 10.75% Subordinated Notes, due 2023, net of unamortized deferred finance costs of $1,084 ​ ​ — ​ ​ 26,847 ​ ​ ​ 535,815 ​ ​ 661,095 Less current portion ​ ​ (61,483) ​ ​ (70,350) Long-term portion ​ $ 474,332 ​ $ 590,745 ​ On January 28, 2020, except for the Sinosure Credit Facility and the 8.5% Senior Notes, the principal outstanding as of December 31, 2019 on all of the Company’s other debt facilities reflected in the above table were paid off or repurchased and the underlying credit agreements or Indentures were terminated or discharged in accordance with their respective terms in conjunction with the Company closing on the 2020 Debt Facilities, described below. ​ Capitalized terms used hereafter have the meaning given in these consolidated financial statements or in the respective transaction documents referred to below, including subsequent amendments thereto. ​ ​ 2020 Debt Facilities ​ On January 23, 2020, International Seaways, Inc., International Seaways Operating Corporation (the “Borrower”) and certain of their subsidiaries entered into a credit agreement (the “Credit Agreement”) comprising $390 million of secured debt facilities (the “2020 Debt Facilities”) with Nordea Bank Abp, New York Branch (“Nordea”), ABN AMRO Capital USA LLC (“ABN”), Crédit Agricole Corporate & Investment Bank, DNB Capital LLC and Skandinaviska Enskilda Banken AB (PUBL), or their respective affilates, as mandated lead arrangers and bookrunners, and BNP Paribas and Danish Ship Finance A/S, as lead arrangers. Nordea is acting as administrative agent, collateral agent and security trustee under the Credit Agreement, and ABN is acting as sustainability coordinator. ​ The 2020 Debt Facilities consist of (i) a five-year senior secured term loan facility in an aggregate principal amount of $300 million (the “Core Term Loan Facility”); (ii) a five-year revolving credit facility in an aggregate principal amount of $40 million (the “Core Revolving Facility”); and (iii) a senior secured term loan credit facility with a maturity date of June 30, 2022 in an aggregate principal amount of $50 million (the “Transition Term Loan Facility”). The Core Term Loan Facility contains an uncommitted accordion feature whereby, for a period of up to 18 months following the closing date, the amount of the loan thereunder may be increased up to an additional $100 million for the acquisition of Additional Vessels, subject to certain conditions. ​ The Core Term Loan Facility and the Core Revolving Facility are secured by a first lien on 14 of the Company’s vessels built in 2009 or later (the “Core Collateral Vessels”), along with their earnings, insurances and certain other assets, while the Transition Term Loan Facility was secured by a first lien on 12 of the Company’s vessels built in 2006 or earlier (the “Transition Collateral Vessels”), along with their earnings, insurances and certain other assets. In addition, both facilities are secured by liens on the collateral relating to the other facilities, as well as certain additional assets of the Borrower. ​ On January 28, 2020, the available amounts under the Core Term Loan Facility and the Transition Term Loan Facility were drawn in full, and $20 million of the $40 million available under the Core Revolving Facility was also drawn. Those proceeds, together with available cash, were used to (i) repay the $331.5 million outstanding principal balance under the 2017 Debt Facilities, (ii) repay the $23.2 million outstanding principal balance under the ABN Term Loan Facility, (iii) repurchase the $27.9 million outstanding principal amount of the Company’s 10.75% subordinated notes due 2023 issued pursuant to an indenture dated June 13, 2018 with GLAS Trust Company LLC, as trustee, as amended, and (iv) pay certain expenses related to the refinancing, including certain structuring and arrangement fees, commitment, legal and administrative fees. ​ The Core Term Loan Facility amortizes in 19 quarterly installments of approximately $9.5 million commencing June 30, 2020 and matures on January 23, 2025, with a balloon payment of approximately $120 million due at maturity. The Core Revolving Facility also matures on January 23, 2025. The Transition Term Loan Facility was scheduled to amortize in 10 quarterly installments of $5 million commencing March 31, 2020 through June 30, 2022. The maturity dates for the 2020 Debt Facilities are subject to acceleration upon the occurrence of certain events (as described in the Credit Agreement). ​ On March 4, 2020, the $20 million outstanding balance under the Core Revolving Facility was repaid in full using available cash on hand and on August 10, 2020, the $40 million outstanding principal balance under the Transition Term Loan Facility was repaid in full using available cash on hand. ​ On March 12, 2020, the Company entered into a Side Letter agreement with the 2020 Debt Facilities lenders relating to the mortgage for the Seaways Mulan, a 2002-built VLCC that has been held by the Indonesian authorities since February 8, 2020 pending the completion of their investigation of a claim that the master had illegally anchored in Indonesian territorial waters while awaiting orders for its next voyage. The mortgage requires the vessel owner to secure the release of a vessel that has been arrested or taken into custody under color of legal authority within 30 days of the initial detention of such vessel and grants the vessel owner an additional 30 days thereafter to cure the non-release of the vessel before being considered to be in default under the terms of the Credit Agreement. If the vessel’s status was not cured or waived by April 8, 2020, the Company would be in default under the terms of the Credit Agreement. Accordingly, pursuant to the terms of the Side Letter agreement, the Lenders granted the Company an additional 60 days from the initial date to secure the release of the Seaways Mulan from arrest by the Indonesian authorities by May 8, 2020 after which the Company would have an additional 30 days (i.e., through June 7, 2020) to cure the non-release of the vessel before being considered to be in default under the terms of the Credit Agreement. On May 15, 2020, the Lenders updated the Side Letter and granted the Company an additional 60 days from May 8, 2020 to secure the release of the Seaways Mulan from arrest by the Indonesian authorities by July 8, 2020 after which the Company would have an additional 30 days (i.e., through August 7, 2020) to cure the non-release of the vessel before being considered to be in default under the terms of the Credit Agreement. The Seaways Mulan was released and allowed to sail out of Indonesian territorial waters on June 9, 2020 and was ultimately redelivered back to the Tankers International Pool on June 28, 2020. ​ On April 27, 2020, the Company entered into a first amendment (the “First Amendment”) of the 2020 Debt Facilities. The First Amendment, among other things, (i) corrects the definition of “Adjusted LIBOR Rate” to reflect the zero percent LIBOR floor previously agreed among the parties; (ii) clarifies the definition of “Permitted Charter” by noting that the time period specified therein does not include any specified or actual redelivery period extending past the initial charter term, and (iii) permits electronic execution of documents relating to the Credit Agreement. ​ Interest on the Core Term Loan Facility and the Core Revolving Facility (together, the “Core Facilities”) is calculated based upon LIBOR plus the Applicable Core Margin (each as defined in the Credit Agreement). The initial Applicable Core Margin of 2.60%, will be adjusted down or up by 0.20% based on the Company’s total leverage ratio, with a leverage ratio of less than 4.0:1 reducing the Applicable Core Margin to 2.40% and a leverage ratio of 6.0:1 or greater increasing the Applicable Core Margin to 2.80%. Borrowings under the Transition Term Loan Facility bore interest at LIBOR plus 3.50%. ​ The Core Facilities also include a sustainability-linked pricing mechanism. The adjustment in pricing will be linked to the carbon efficiency of the INSW fleet as it relates to reductions in CO2 emissions year-over-year, such that it aligns with the International Maritime Organization’s 50% industry reduction target in GHG emissions by 2050. This key performance indicator is to be calculated in a manner consistent with the de-carbonization trajectory outlined in the Poseidon Principles, the global framework by which financial institutions can assess the climate alignment of their ship finance portfolios relative to established de-carbonization trajectories. The Company will be required to deliver a sustainability certificate commencing with the year ending December 31, 2021. If the fleet sustainability score in respect of the relevant year is lower than the fleet sustainability score for the prior year, the Applicable Core Margin will be decreased by 0.025% per annum, while if the score is higher than that of the previous year, the Applicable Core Margin will be increased by that same amount (but in no case will any such adjustment result in the Applicable Core Margin being increased or decreased from the otherwise-applicable Applicable Core Margin by more than 0.025% per annum in the aggregate). ​ Sinosure Credit Facility ​ In June 2018, as part of the acquisition of six VLCCs, the Company financed the acquisition price of 1 2/3% ​ The Company paid to Euronav cash consideration of approximately $120.0 million, with the difference reflecting assumed debt and accrued interest thereon through the closing date. Supplemental cash flow information for the year ended December 31, 2018 associated with the aforementioned non-cash assumption of debt in relation to the acquisition of six VLCCs aggregating $311.0 million were non-cash investing activities and financing activities. ​ ​ 8.5% Senior Notes ​ On May 31, 2018, the Company completed a registered public offering of $25 million aggregate principal amount of its 8.5% senior unsecured notes due 2023 (the “8.5% Senior Notes”), which resulted in aggregate net proceeds to the Company of approximately $23.5 million, after deducting commissions and estimated expenses. The Company used the net proceeds to fund the acquisition of 6 VLCCs described above, to repay a portion of its then outstanding 2017 Term Loan Facility and for general corporate purposes. ​ The Company issued the Notes under an indenture dated as of May 31, 2018 (the “Base Indenture”), between the Company and The Bank of New York Mellon, as trustee (the “Trustee”), as supplemented by a supplemental indenture dated as of May 31, 2018 (the “First Supplemental Indenture” and, together with the Base Indenture, the “Indenture”), between the Company and the Trustee. The Notes will mature on June 30, 2023 and bear interest at a rate of 8.50% per annum. Interest on the Notes is payable in arrears on March 30, June 30, September 30 and December 30 of each year. The terms of the Indenture, among other things, limit the Company’s ability to merge, consolidate or sell assets. ​ The Company may redeem the Notes at its option, in whole or in part, at any time on or after June 30, 2020 at a redemption price equal to 100% of their principal amount, plus accrued and unpaid interest to, but excluding, the redemption date. In addition, if the Company undergoes a Change of Control (as defined in the Indenture) the Company may be required to repurchase all of the Notes at a purchase price equal to 101% of the principal amount of the Notes, plus accrued and unpaid interest (including additional interest, if any), to, but excluding, the repurchase date. ​ Debt Covenants ​ The Company was in compliance with the financial and non-financial covenants under all of its debt facilities as of December 31, 2020. ​ The 2020 Debt Facilities contain customary representations, warranties, restrictions and covenants applicable to the Company, the Borrower and the subsidiary guarantors (and in certain cases, other subsidiaries), including financial covenants that require the Company (i) to maintain a minimum liquidity level of the greater of $50 million and 5% of the Company’s Consolidated Indebtedness; (ii) to ensure the Company’s and its consolidated subsidiaries’ Maximum Leverage Ratio will not exceed 0.60 to 1.00 at any time; (iii) to ensure that Current Assets exceeds Current Liabilities (which is defined to exclude the current potion of Consolidated Indebtedness); (iv) to ensure the aggregate Fair Market Value of the Core Collateral Vessels will not be less than 135% of the aggregate outstanding principal amount of the Core Term Loans and Revolving Loans and the aggregate Fair Market Value of the Transition Collateral Vessels will not be less than 175% of the aggregate outstanding principal amount of the Transition Term Loans, respectively; and (v) to ensure the ratio of Consolidated EBITDA to Consolidated Cash Interest Expense will not be lower than (A) 2.25:1.00, for the period ending on June 30, 2020 and (B) 2.50:1.00 at all times thereafter. ​ Under the Sinosure Credit Facility, the Obligors (as defined in the Sinosure Credit Facility) are required to comply with various collateral maintenance and financial covenants, including with respect to: ​ (i) minimum security coverage, which shall not be less than 135% of the aggregate loan principal outstanding under the Sinosure Credit Facility. Any non-compliance with the minimum security coverage shall not constitute an event of default so long as within thirty days of such non-compliance, Seaways Subsidiary VII, Inc. has either provided additional collateral or prepaid a portion of the outstanding loan balance to cure such non-compliance ; ​ (ii) maximum consolidated leverage ratio, which shall not be greater than 0.60 to 1.00 on any testing date ; ​ (iii) minimum consolidated liquidity, under which unrestricted consolidated cash and cash equivalents shall be no less than $25 million at any time and total consolidated cash and cash equivalents (including cash restricted under the Sinosure Credit Facility) shall not be less than the greater of $50 million or 5.0% of Total Indebtedness (as defined in the Sinosure Credit Facility) or $9 million (i.e., $1,500 per each VLCC securing the Sinosure Credit Facility); and ​ (iv) interest expense coverage ratio, which for Seaways Holding Corporation, shall not be less than 2.00 to 1.00 during the period commencing on July 1, 2018 through June 30, 2019 and will be calculated on a trailing six, nine and twelve-month basis from December 31, 2018, March 31, 2019 and June 30, 2019, respectively. For the Company, the interest expense coverage ratio shall not be less than 2.25 to 1.00 for the period commencing on July 1, 2019 through June 30, 2020 and no less than 2.50 to 1.00 for the period commencing on July 1, 2020 and thereafter and shall be calculated on a trailing twelve-month basis. No event of default under this covenant will occur if the failure to comply is capable of remedy and is remedied within thirty days of the Facility Agent giving notice to the Company or (if earlier) any Obligor becoming aware of the failure to comply, and (i) if such action is being taken with respect to a Test Date falling on or prior to December 31, 2020, then such remedy shall be in the form of cash and cash equivalents being (or having been) deposited by Seaways Holding Corporation to a restricted Minimum Liquidity Account within the thirty day period mentioned above in the manner and in the amounts required to remedy such breach as tested at the Seaways Holding Corporation level and (ii) if such action is being taken with respect to a Test Date falling on or after January 1, 2021, then any such remedy and the form of the same shall be considered and determined by the lenders under the Sinosure Credit Facility in their absolute discretion . ​ The 8.5% Senior Notes Indenture contains certain restrictive covenants, including covenants that, subject to certain exceptions and qualifications, restrict our ability to make certain payments if a default under the Indenture has occurred and is continuing or will result therefrom and require us to limit the amount of debt we incur, maintain a certain minimum net worth and provide certain reports. The Indenture also provides for certain customary events of default (subject, in certain cases, to receipt of notice of default and/or customary grace or cure periods). ​ Pursuant to the limitation on borrowings covenant, the Company shall not permit Total Borrowings (as defined in the Indenture) to equal or exceed 70% of Total Assets (as defined in the Indenture). The Company shall also ensure that Net Worth (defined as Total Assets, less Intangible assets and Total Borrowings, as defined in the Indenture) exceeds $600 million pursuant to the Minimum Net Worth covenant. ​ The Company’s credit facilities also require it to comply with a number of covenants, including the delivery of quarterly and annual financial statements, budgets and annual projections; maintaining required insurances; compliance with laws (including environmental); compliance with the Employee Retirement Income Security Act of 1974 (“ERISA”); maintenance of flag and class of the collateral vessels; restrictions on consolidations, mergers or sales of assets; limitations on liens; limitations on issuance of certain equity interests; limitations on transactions with affiliates; and other customary covenants and related provisions. ​ While the Company was in compliance with all of its debt covenants as of December 31, 2020, the currently forecasted decline in average daily TCE rates across all vessel classes during 2021 could cause the Company to breach the Interest Coverage Ratio covenant under the Core Term Loan Facility and the Sinosure Credit Facility at the end of the third quarter of 2021. If the Company breaches such covenant and is unable to remedy the relevant breach or obtain a waiver, the Company’s lenders could accelerate its debt and the lenders under the 2020 Debt Facilities and the Sinosure Credit Facility could foreclose on the 20 vessels pledged by the Company. In addition to obtaining a waiver from its lenders or deploying some of its vessels on time charters at rates above the currently forecasted spot rates in order to increase the Company’s Consolidated EBITDA, the Company has a number of actions it can independently take to avoid a potential covenant breach. Such possible actions include reducing interest expense by paying off the Company’s outstanding interest rate swaps during the first quarter of 2021. Interest Expense ​ The following table summarizes interest expense, including amortization of issuance and deferred financing costs (for additional information related to deferred financing costs see Note 2, “Significant Accounting Policies”), commitment, administrative and other fees, recognized during the years ended December 31, 2020, 2019 and 2018 with respect to the Company’s debt facilities: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (Dollars in thousands) ​ 2020 ​ 2019 ​ 2018 Core Term Loan Facility, due 2025 ​ $ 13,542 ​ $ — ​ $ — Transition Term Loan Facility ​ ​ 1,518 ​ ​ — ​ ​ — Core Revolving Facility ​ ​ 660 ​ ​ — ​ ​ — 2017 Term Loan Facility ​ ​ 3,628 ​ ​ 41,483 ​ ​ 45,601 2017 Revolver Facility ​ ​ 63 ​ ​ 848 ​ ​ 475 ABN Term Loan Facility ​ ​ 107 ​ ​ 1,716 ​ ​ 1,024 Sinosure Credit Facility, due 2027 - 2028 ​ ​ 13,684 ​ ​ 14,903 ​ ​ 8,350 8.5% Senior Notes, due 2023 ​ ​ 2,417 ​ ​ 2,390 ​ ​ 1,396 10.75% Subordinated Notes ​ ​ 276 ​ ​ 3,642 ​ ​ 2,032 Total debt related interest expense ​ $ 35,895 ​ $ 64,982 ​ $ 58,878 ​ The following table summarizes interest paid, excluding deferred financing fees paid, during the years ended December 31, 2020, 2019 and 2018 with respect to the Company’s debt facilities: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (Dollars in thousands) ​ 2020 ​ 2019 ​ 2018 Core Term Loan Facility, due 2025 ​ $ 12,024 ​ $ — ​ $ — Transition Term Loan Facility ​ ​ 1,183 ​ ​ — ​ ​ — Core Revolving Facility ​ ​ 471 ​ ​ — ​ ​ — 2017 Term Loan Facility ​ ​ 2,011 ​ ​ 36,236 ​ ​ 42,825 2017 Revolver Facility ​ ​ 53 ​ ​ 710 ​ ​ 442 ABN Term Loan Facility ​ ​ 156 ​ ​ 1,504 ​ ​ 795 Sinosure Credit Facility, due 2027 - 2028 ​ ​ 12,199 ​ ​ 14,200 ​ ​ 7,225 8.5% Senior Notes, due 2023 ​ ​ 2,130 ​ ​ 2,130 ​ ​ 1,250 10.75% Subordinated Notes ​ ​ 359 ​ ​ 3,021 ​ ​ 1,591 Total debt related interest expense paid ​ $ 30,586 ​ $ 57,801 ​ $ 54,128 ​ Debt Modifications, Repurchases and Extinguishments ​ During the year ended December 31, 2020, the Company incurred debt issuance costs aggregating $7.3 million in connection with 2020 Debt Facilities. Issuance costs paid to lenders and third-party fees associated with the Core Revolving Facility aggregating $0.8 million were capitalized as deferred finance charges. Issuance costs paid to lenders and third-party fees associated with Core Term Loan Facility and Transition Term Loan Facility totaled $6.5 million, of which $6.3 million were capitalized as deferred finance charges and $0.2 million associated with third-party fees paid that were deemed to be a modification were expensed and are included in third-party debt modification fees in the accompanying consolidated statement of operations. Issuance costs incurred and capitalized as deferred finance charges have been treated as a reduction of debt proceeds. ​ In connection with the repurchases and extinguishment of the Company’s debt facilities, the Company recognized aggregate net losses of $14.3 million during the year ended December 31, 2020, which are included in other expense in the accompanying consolidated statement of operations. The net losses reflect (i) prepayment fees of $1.0 million related to the 10.75% Subordinated Notes and a write-off of $12.5 million of unamortized original issue discount and deferred financing costs associated with the payoff of the 2017 Term Loan, ABN Term Loan Facility, and the 10.75% Subordinated Notes, which were treated as extinguishments during the first quarter of 2020, and (ii) prepayment fees of $0.2 million and a write-off of $0.6 million of unamortized deferred financing costs associated with the payoff of the Transition Term Loan Facility in August 2020, which was treated as an extinguishment. ​ I n connection with the $10 and the $100 prepayment of the in July 2019 and October 2019, respectively, which were treated as a partial extinguishments, the Company recognized aggregate net losses of included in other expense in the consolidated statement of operations. The net losses reflect a 1% prepayment fee of $1.1 and a write-off of $3.6 of unamortized original issue discount and deferred financing costs. ​ During the year ended December 31, 2018, the Company incurred debt issuance and amendment costs aggregating $14.6 million in connection with the ABN Term Loan Facility, Sinosure Credit Facility, 8.5% Senior Notes, 10.75% Subordinated Notes (and the subsequent amendment thereto), and the 2017 Debt Facilities Second Amendment. (See Note 2, “Significant Accounting Policies,” for additional information relating to deferred financing charges). Debt issuance and amendment fees paid to all lenders and third-party fees associated with the ABN Term Loan Facility, Sinosure Credit Facility, 8.5% Senior Notes, and 10.75% Subordinated Notes totaled $7.7 million, of which $7.6 million were capitalized as deferred finance charges and $0.1 million was expensed and is included in third-party debt modification fees in the consolidated statement of operations. Debt amendment fees paid to lenders and third-party fees associated with the 2017 Debt Facilities Second Amendment totaled $6.9 million, of which $4.4 million were capitalized as deferred finance charges. The remaining $2.5 million was expensed, of which $1.2 million is included in third-party debt modification fees in the consolidated statement of operations and $1.3 million of debt extinguishment costs are included in other expense in the consolidated statement of operations. In addition, aggregate net losses of $2.4 million for the year ended December 31, 2018 recognized on the repurchases of the Company’s debt facilities, is included in other expense in the consolidated statement of operations. The net loss reflects a write-off of unamortized original issue discount and deferred financing costs associated with the principal prepayment of $60 million made in connection with the 2017 Debt Facilities Second Amendment and the repurchase of $2.1 million of the 10.75% Subordinated Notes, which were treated as partial extinguishments. Debt issuance and amendment costs incurred and capitalized as deferred finance charges have been treated as a reduction of debt on the consolidated balance sheets. ​ As of December 31, 2020, the aggregate annual principal payments required to be made on the Company’s debt facilities are as follows: ​ ​ ​ ​ ​ (Dollars in thousands) ​ Amount 2021 ​ $ 61,483 2022 ​ ​ 61,483 2023 ​ ​ 86,484 2024 ​ ​ 61,483 2025 ​ ​ 143,532 Thereafter ​ ​ 128,233 Aggregate principal payments required ​ $ 542,698 ​

FAIR VALUE OF FINANCIAL INSTRUM

FAIR VALUE OF FINANCIAL INSTRUMENTS, DERIVATIVES AND FAIR VALUE DISCLOSURES	12 Months Ended
	Dec. 31, 2020
FAIR VALUE OF FINANCIAL INSTRUMENTS, DERIVATIVES AND FAIR VALUE DISCLOSURES [Abstract]
FAIR VALUE OF FINANCIAL INSTRUMENTS, DERIVATIVES AND FAIR VALUE DISCLOSURES	NOTE 9 — FAIR VALUE OF FINANCIAL INSTRUMENTS, DERIVATIVES AND FAIR VALUE DISCLOSURES: ​ The estimated fair values of the Company’s financial instruments, other than derivatives that are not measured at fair value on a recurring basis, categorized based upon the fair value hierarchy, at December 31, 2020 and 2019 are as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (Dollars in thousands) ​ Fair Value ​ Level 1 ​ Level 2 December 31, 2020: ​ ​ ​ ​ ​ ​ ​ ​ ​ Cash and cash equivalents (1) ​ $ 215,677 ​ $ 215,677 ​ $ — Core Term Loan Facility ​ ​ (271,571) ​ ​ — ​ ​ (271,571) Sinosure Credit Facility ​ ​ (246,127) ​ ​ — ​ ​ (246,127) 8.5% Senior Notes ​ ​ (25,697) ​ ​ (25,697) ​ ​ — ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2019: ​ ​ ​ ​ ​ ​ ​ ​ ​ Cash and cash equivalents (1) ​ $ 150,243 ​ $ 150,243 ​ $ — 2017 Term Loan Facility ​ ​ (333,177) ​ ​ — ​ ​ (333,177) ABN Term Loan Facility ​ ​ (23,248) ​ ​ — ​ ​ (23,248) Sinosure Credit Facility ​ ​ (269,705) ​ ​ — ​ ​ (269,705) 8.5% Senior Notes ​ ​ (26,120) ​ ​ (26,120) ​ ​ — 10.75% Subordinated Notes ​ ​ (32,649) ​ ​ — ​ ​ (32,649) (1) Includes non-current restricted cash of $16.3 million and $60.6 million at December 31, 2020 and 2019, respectively. ​ Derivatives ​ The Company uses interest rate caps, collars and swaps for the management of interest rate risk exposure associated with changes in LIBOR interest rate payments due on its credit facilities. T ● Balance of 2019 through December 31, 2020: cap rate of 1.98%, floor rate of 1.98%; and ● December 31, 2020 through December 31, 2022: cap rate of 2.26%, floor rate of 1.25%. ​ The Company determined that as of September 30, 2019 remained so classified until the forecasted interest accrual transactions either affect earnings or become not probable of occurring. ​ In connection with its entry into the Core Term Loan Facility (see Note 8, “Debt”) on January 28, 2020, the Company, in a cashless transaction, converted the $350 million notional into an amortizing $250 million notional pay-fixed, receive-three-month LIBOR interest rate swap subject to a 0% floor. The term of the new hedging arrangement was extended to coincide with the maturity of the Core Term Loan Facility of January 23, 2025 at a fixed rate of 1.97% . The interest rate swap agreement has been re-designated and qualifies as a cash flow hedge and contains no leverage features. Changes in the fair value of the prior to the re-designation on January 28, 2020 recorded through earnings during the first quarter of 2020 totaled a loss of $1.3 million. ​ On April 16, 2020, the Company entered into an interest rate swap agreement with a major financial institution covering a notional amount of $25 million of the Core Term Loan Facility that effectively converts the Company’s interest rate exposure from a three-month LIBOR floating rate to a fixed rate of 0.50% through the maturity date of January 23, 2025 , effective June 30, 2020. The interest rate swap agreement, which contains no leverage features, is designated and qualifies as a cash flow hedge. ​ The Company was also party to a floating-to-fixed interest rate swap agreement with a major financial institution covering the balance outstanding under the Sinosure Credit Facility that effectively converts the Company’s interest rate exposure from a floating rate based on three-month LIBOR to a fixed rate of 2.99% through the termination date of March 21, 2022. The interest rate swap agreement was designated and qualified as a cash flow hedge and contained no leverage features. In May 2019, the Company extended the maturity date of the interest rate swap from March 21, 2022 to March 21, 2025 and reduced the fixed three-month rate from 2.99% to 2.76%, effective March 21, 2019. In July 2020, the Company extended the maturity date of the interest rate swap from March 21, 2025 to December 21, 2027 and reduced the fixed three-month LIBOR rate from 2.76% to 2.35% , effective June 21, 2020. The new interest rate swap agreement does not in its entirety meet the definition of a derivative instrument because of its off market fixed rate at inception and is deemed to be a hybrid instrument with a financing component and an embedded at-the-market derivative. Such embedded derivative is bifurcated and accounted for separately in the same manner as the Company’s other derivatives. The financing component is recorded in current and noncurrent other liabilities on the consolidated balance sheet at amortized cost. Due to an other-than-insignificant financing element on a portion of such hybrid instrument, the cash flows associated with this hybrid instrument are classified as financing activities in the consolidated statement of cash flows. ​ ​ Tabular disclosure of derivatives location Derivatives are recorded on a net basis by counterparty when a legal right of offset exists. The Company had the following amounts recorded on a gross basis by transaction in the accompanying consolidated balance sheets related to the Company’s use of derivatives as of ​ Fair Values of Derivative Instruments: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (Dollars in thousands) ​ Long-term derivative ​ Current portion of derivative liability ​ Long-term derivative ​ Accounts payable, accrued expenses and other current liabilities ​ Other December 31, 2020: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Derivatives designated as cash flow hedges: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Interest rate swaps ​ $ 2,129 ​ $ (4,121) ​ $ (6,155) ​ $ — ​ $ — ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Other-than-insignificant financing element of derivatives: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Interest rate swaps (1) ​ ​ — ​ ​ — ​ ​ — ​ ​ (2,979) ​ ​ (14,051) Total ​ $ 2,129 ​ $ (4,121) ​ $ (6,155) ​ $ (2,979) ​ $ (14,051) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31,2019: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Derivatives designated as cash flow hedges: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Interest rate swaps ​ $ — ​ $ (2,384) ​ $ (5,968) ​ $ — ​ $ — ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Derivatives not designated as cash flow hedges: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Interest rate collar ​ ​ — ​ ​ (1,230) ​ ​ (577) ​ ​ — ​ ​ — Total ​ $ — ​ $ (3,614) ​ $ (6,545) ​ $ — ​ $ — (1) Represents the financing element of the hybrid instrument discussed above, which is recorded at amortized cost. ​ The following tables present information with respect to gains and losses on derivative positions reflected in the consolidated statements of operations or in the consolidated statements of other comprehensive loss. ​ The effect of cash flow hedging relationships recognized in other comprehensive loss excluding amounts reclassified from accumulated other comprehensive loss, including hedges of equity method investees, for the three years ended December 31, 2020 follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (Dollars in thousands) ​ 2020 ​ 2019 ​ 2018 Derivatives designated as hedging instruments: ​ ​ ​ ​ ​ ​ ​ Interest rate swaps ​ $ (20,123) ​ $ (15,221) ​ $ (1,948) Interest rate cap/collar ​ ​ — ​ ​ (3,905) ​ ​ 261 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Other-than-insignificant financing element of derivatives: ​ ​ ​ ​ ​ ​ ​ Interest rate swaps ​ ​ (1,380) ​ ​ — ​ ​ — Total other comprehensive loss ​ $ (21,503) ​ $ (19,126) ​ $ (1,687) ​ ​ The effect of cash flow hedging relationships on the consolidated statements of operations is presented excluding hedges of equity method investees. The effect of the Company’s cash flow hedging relationships on the consolidated statement of operations for the three years ended December 31, 2020 is shown below: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (Dollars in thousands) ​ 2020 ​ 2019 ​ 2018 Derivatives designated as hedging instruments: ​ ​ ​ ​ ​ ​ ​ Interest rate swaps ​ $ 4,571 ​ $ 1,467 ​ $ 471 Interest rate cap/collar ​ ​ — ​ ​ 99 ​ ​ 21 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Derivatives not designated as hedging instruments: ​ ​ ​ ​ ​ ​ ​ Interest rate collar ​ ​ 1,352 ​ ​ (65) ​ ​ — ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Other-than-insignificant financing element of derivatives: ​ ​ ​ ​ ​ ​ ​ Interest rate swaps ​ ​ 3,376 ​ ​ — ​ ​ — Total interest expense ​ $ 9,299 ​ $ 1,501 ​ $ 492 ​ See Note 6, “Equity Method Investments,” for additional information relating to derivatives held by the Company’s equity method investees and Note 13, “Accumulated Other Comprehensive Loss,” for disclosures relating to the impact of derivative instruments on accumulated other comprehensive loss. ​ Fair Value Hierarchy ​ The following table presents the fair values, which are pre-tax, for assets and liabilities measured on a recurring basis (excluding investments in affiliated companies): ​ ​ ​ ​ ​ ​ ​ ​ ​ (Dollars in thousands) ​ ​ Fair Value ​ ​ Level 2 (1) ​ Assets/(Liabilities) at December 31, 2020: ​ ​ ​ ​ ​ ​ ​ Derivative Assets (interest rate swaps) ​ $ 2,129 ​ $ 2,129 ​ Derivative Liabilities (interest rate swaps) ​ ​ (10,276) ​ ​ (10,276) ​ ​ ​ ​ ​ ​ ​ ​ ​ Assets/(Liabilities) at December 31, 2019: ​ ​ ​ ​ ​ ​ ​ Derivative Assets (interest rate swaps and collar) ​ $ — ​ $ — ​ Derivative Liabilities (interest rate swaps and collar) ​ ​ (10,159) ​ ​ (10,159) ​ (1) For the interest rate cap, collar and swaps, fair values are derived using valuation models that utilize the income valuation approach. These valuation models take into account contract terms such as maturity, as well as other inputs such as interest rate yield curves and creditworthiness of the counterparty and the Company. ​ ​ The following table summarizes the fair values of assets for which an impairment charge was recognized for the year ended December 31, 2020: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Impairment (Dollars in thousands) ​ Fair Value ​ Level 2 ​ Charges Assets: ​ ​ ​ ​ ​ ​ ​ ​ ​ Crude Tankers - Vessels held for use (1)(2) ​ $ 134,035 ​ $ 134,035 ​ $ (47,265) Product Carriers - Vessels held for use (1)(2) ​ $ 113,250 ​ $ 113,250 ​ $ (55,757) (1) Pre-tax impairment charges of $5.5 million related to one VLCC tanker, $11.7 million related to two VLCC tankers, and $30.1 million related to one VLCC tanker and one Aframax in the Crude Tankers segment were recorded during the three-month periods ended June 30, 2020, September 30, 2020, and December 31, 2020, respectively . Pre-tax impairment charges of $55.7 million related to two LR1s and four MRs in the Product Carriers segment were recorded during the three-month period ended December 31, 2020. (2) The fair value measurement of $30.4 million that was used to determine the impairment for one VLCC at June 30, 2020, the fair value measurement of $50.5 million that was used to determine the impairment for two VLCCs at September 30, 2020, and the fair value measurement of $53.1 millon that was used to determine the impairment for one VLCC and one Aframax, and $113.3 million that was used to determine the impairment of two LR1s and four MRs at December 31, 2020, were based upon a market approach, which considered the expected sales price of the vessel obtained from vessel appraisals and executed memoranda of agreements for the sale of each of the vessels as discussed in Note 5, “Vessels.” As sales of vessels occur somewhat infrequently, the expected sales price is considered to be Level 2.

ACCOUNTS PAYABLE, ACCRUED EXPEN

ACCOUNTS PAYABLE, ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES	12 Months Ended
	Dec. 31, 2020
ACCOUNTS PAYABLE, ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES [Abstract]
ACCOUNTS PAYABLE, ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES	NOTE 10 — ACCOUNTS PAYABLE, ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES: ​ ​ ​ ​ ​ ​ ​ ​ (Dollars in thousands) ​ December 31, 2020 ​ December 31, 2019 Accounts payable ​ $ 2,609 ​ $ 4,988 Payroll and benefits ​ ​ 6,293 ​ ​ 5,585 Interest ​ ​ 370 ​ ​ 594 Other-than-insignificant financing element of derivatives ​ ​ 2,979 ​ ​ — Due to owners on chartered in vessels ​ ​ 787 ​ ​ 1,108 Accrued drydock, repairs and vessel betterment costs ​ ​ 6,247 ​ ​ 3,150 Bunkers and lubricants ​ ​ 656 ​ ​ 538 Charter revenues received in advance ​ ​ 3,060 ​ ​ 272 Insurance ​ ​ 493 ​ ​ 539 Accrued vessel expenses ​ ​ 8,779 ​ ​ 8,003 Accrued general and administrative expenses ​ ​ 940 ​ ​ 1,052 Other ​ ​ 1,212 ​ ​ 1,725 Total accounts payable, accrued expense and other current liabilities ​ $ 34,425 ​ $ 27,554 ​

TAXES

TAXES	12 Months Ended
	Dec. 31, 2020
TAXES [Abstract]
TAXES	NOTE 11 —TAXES: ​ Income taxes are provided using the asset and liability method, such that income taxes are recorded based on amounts refundable or payable in the current year and include the results of any differences in the basis of assets and liabilities between U.S. GAAP and tax reporting. The Company derives substantially all of its gross income from the use and operation of vessels in international commerce. The Company’s entities that own and operate vessels are primarily domiciled in the Marshall Islands, which does not impose income tax on shipping operations. The Company also has or had subsidiaries in various jurisdictions that performed administrative, commercial or technical management functions. These subsidiaries are subject to income taxes based on the services performed in countries in which those particular offices are located and, accordingly, current and deferred income taxes are recorded. ​ INSW, including its subsidiaries, which are disregarded entities for U.S. Federal income tax purposes, is exempt from taxation on its U.S. source shipping income under Section 883 of the U.S. Internal Revenue Code of 1986, as amended (the “Code”) and U.S. Treasury Department regulations. INSW qualified for this exemption because its common shares were treated as primarily and regularly traded on an established securities market in the United States or another qualified country and for more than half of the days in the taxable year ended December 31, 2020, less than 50 percent of the total vote and value of the Company’s stock was held by one or more shareholders who each owned 5% or more of the vote and value of the Company’s stock. Beginning in 2021, to the extent INSW is unable to qualify for exemption from tax under Section 883, INSW will be subject to U.S. federal taxation of 4% of its U.S. source shipping income on a gross basis without the benefit of deductions. Shipping income that is attributable to transportation that begins or ends, but that does not both begin and end, in the U.S. will be considered to be 50% derived from sources within the U.S. Shipping income attributable to transportation that both begins and ends in the U.S. will be considered to be 100% derived from sources within the U.S. INSW does not engage in transportation that gives rise to 100% U.S. source income. Shipping income attributable to transportation exclusively between non-U.S. ports will be considered to be 100% derived from sources outside the U.S. Shipping income derived from sources outside the U.S. will not be subject to any U.S. federal income tax. INSW’s vessels operate in various parts of the world, including to or from U.S. ports. There can be no assurance that INSW will continue to qualify for the Section 883 exemption. ​ A substantial portion of income earned by INSW is not subject to income tax, and no deferred taxes are provided on the temporary differences between the tax and financial statement basis of the underlying assets and liabilities for those subsidiaries not subject to income tax in their respective countries of incorporation. ​ The Marshall Islands impose tonnage taxes, which are assessed on the tonnage of certain of the Company’s vessels. These tonnage taxes are included in vessel expenses in the accompanying consolidated statements of operations. ​ The components of the income tax (provision)/benefit follow: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (Dollars in thousands) ​ ​ 2020 ​ ​ 2019 ​ ​ 2018 ​ Current ​ $ (1) ​ $ (1) ​ $ 105 ​ Deferred ​ ​ — ​ ​ — ​ ​ — ​ Income tax (provision)/benefit ​ $ (1) ​ $ (1) ​ $ 105 ​ ​ The differences between income taxes expected at the Marshall Islands statutory income tax rate of zero percent and the reported income tax (provisions)/benefits are summarized as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2020 ​ ​ 2019 ​ ​ 2018 ​ Change in valuation allowance ​ ​ 0.66 % ​ 0.66 % ​ (0.66) % Income subject to tax in other jurisdictions ​ ​ (0.65) % ​ (0.83) % ​ 0.54 % Effective income tax rate ​ ​ 0.01 % ​ (0.17) % ​ (0.12) % ​ The significant components of the Company’s deferred tax liabilities and assets follow: ​ ​ ​ ​ ​ ​ ​ ​ (Dollars in thousands) ​ December 31, 2020 ​ December 31, 2019 Deferred tax assets: ​ ​ ​ ​ ​ ​ Net operating loss carryforwards ​ $ 2,173 ​ $ 1,836 Excess of tax over book basis of depreciable assets ​ ​ 612 ​ ​ 548 Pensions ​ ​ 1,950 ​ ​ 1,797 Total deferred tax assets ​ ​ 4,735 ​ ​ 4,181 Less: Valuation allowance ​ ​ (4,735) ​ ​ (4,181) Deferred tax assets, net ​ ​ — ​ ​ — Net noncurrent deferred tax assets/(liabilities) ​ $ — ​ $ — ​ As of December 31, 2020 and 2019, the Company had net operating loss carryforwards of $11.4 million and $10.8 million, respectively. The net operating loss carryforward of $11.4 million as of December 31, 2020 has an indefinite life. ​ The Company believes that it is more likely than not that the benefit from its net operating loss carryforwards and certain other deferred tax assets will not be realized and has maintained a valuation allowance of $4.7 million and $4.2 million, respectively, as of December 31, 2020 and 2019. If or when recognized, the tax benefits related to any reversal of the valuation allowance on deferred tax assets will be accounted for as a reduction of income tax expense in the period such reversal occurs. During 2020, the Company increased its valuation allowance by $0.5 million primarily as a result of changes in net operating loss carryforwards and the unfunded benefit obligation related to defined benefit pension plan in the United Kingdom. ​ Unrecognized tax benefits (excluding interest and penalties) of $7 thousand as of December 31, 2020 and 2019, are included in other current liabilities in the consolidated balance sheets. ​ The Company records interest on unrecognized tax benefits in its provision for income taxes. Accrued interest is included in other current liabilities in the consolidated balance sheets. As of December 31, 2020 and 2019, the Company has recognized a total liability for interest of $7 thousand and $5 thousand, respectively.

CAPITAL STOCK AND STOCK COMPENS

CAPITAL STOCK AND STOCK COMPENSATION	12 Months Ended
	Dec. 31, 2020
CAPITAL STOCK AND STOCK COMPENSATION [Abstract]
CAPITAL STOCK AND STOCK COMPENSATION	NOTE 12 — CAPITAL STOCK AND STOCK COMPENSATION: ​ The Company accounts for stock compensation expense in accordance with the fair value based method required by ASC 718, Compensation – Stock Compensation ​ Effective November 18, 2016, INSW adopted, incentive compensation plans (the “Incentive Plans” as further described below) in order to facilitate the grant of equity and cash incentives to directors, employees, including executive officers and consultants of the Company and certain of its affiliates and to enable the Company and certain of its affiliates to obtain and retain the services of these individuals, which is essential to our long-term success. INSW reserved 2,000,000 shares for issuance under its management incentive plan and 400,000 shares for issuance under its non-employee director incentive compensation plan. Effective June 22, 2020, INSW adopted new Incentive Plans and reserved an additional 1,400,000 shares for issuance under its management incentive plan and 400,000 shares for issuance under its non-employee director incentive compensation plan. ​ Information regarding share-based compensation awards granted by INSW follows: ​ Director Compensation — Restricted Common Stock ​ INSW awarded a total of 57,317, 51,107 and 47,501 restricted common stock shares during the years ended December 31, 2020, 2019 and 2018, respectively, to its non-employee directors. The weighted average fair value of INSW’s stock on the measurement date of such awards was $16.05 (2020), $18.00 (2019) and $18.82 (2018) per share. Such restricted shares awards vest in full on the earlier of the next annual meeting of the stockholders or anniversary date, subject to each director continuing to provide services to INSW through such date. The restricted share awards granted may not be transferred, pledged, assigned or otherwise encumbered prior to vesting. Prior to the vesting date, a holder of restricted share awards has all the rights of a shareholder of INSW, including the right to vote such shares and the right to receive dividends paid with respect to such shares at the same time as common shareholders generally. ​ On July 8, 2020, Mr. Gregory A. Wright resigned from the Board. Mr. Wright’s resignation was not the result of any disagreement with the Company on any matter relating to the Company’s operations, policies or practices. In connection with his resignation, a total of 6,230 shares previously granted to Mr. Wright (valued at approximately $0.1 million) vested in full on July 8, 2020. In addition, in consideration of the Company’s and the Board’s ability to seek advice from him following his resignation through the end of the second quarter of 2021, the Company paid Mr. Wright approximately $0.1 million in July 2020. ​ Management Compensation ​ (i) Restricted Stock Units ​ During the years ended December 31, 2020, 2019 and 2018, the Company awarded 58,258, 63,998 and 55,536 time-based restricted stock units (“RSUs”) to certain of its employees, including senior officers, respectively. The average grant date fair value of these awards was $21.93 (2020), $17.21 (2019) and $17.46 (2018) per RSU. Each RSU represents a contingent right to receive one share of INSW common stock upon vesting. Each award of RSUs will vest in equal installments on each of the first three anniversaries of the grant date. ​ In addition, in July 2019, the Company granted 26,451 time-based RSUs to its employees. The weighted average grant date fair value of these awards was $19.00 per RSU. Each award of RSUs will vest in equal installments on each of the first two anniversaries of the grant date. ​ Also, in December 2019, the Company granted 44,466 time-based RSUs to certain employees, . The weighted average grant date fair value of these awards was $27.66 per RSU. Each award of RSUs vested on the first anniversary of the grant date. ​ RSUs may not be transferred, pledged, assigned or otherwise encumbered until they are settled. Settlement of vested RSUs may be in either shares of common stock or cash, as determined at the discretion of the Human Resources and Compensation Committee, and shall occur as soon as practicable after the vesting date. If the RSUs are settled in shares of common stock, following the settlement of such shares, the grantee will be the record owner of the shares of common stock and will have all the rights of a shareholder of the Company, including the right to vote such shares and the right to receive dividends paid with respect to such shares of common stock. RSUs which have not become vested as of the date of a grantee’s termination from the Company will be forfeited without the payment of any consideration, unless otherwise provided for. ​ During the years ended December 31, 2020, 2019 and 2018, the Company awarded 58,258 , 63,994 and 55,534 , respectively, performance-based RSUs to its senior officers. The weighted average grant date fair value of the awards with performance conditions was determined to be $17.83 (2020), $17.21 (2019), and $17.46 (2018) per RSU. The weighted average grant date fair value of the TSR (as defined below) based performance awards, which have a market condition, was estimated using a Monte Carlo probability model and determined to be $17.59 (2020), $16.68 (2019) and $18.87 (2018) per RSU. Each performance stock unit represents a contingent right to receive RSUs based upon the covered employees being continuously employed through the end of the period over which the performance goals are measured and shall vest as follows: (i) one-half of the target RSUs shall vest on the third fiscal year end date following the grant date, subject to INSW’s return on invested capital (“ROIC”) performance in the three-year ROIC performance period relative to a target rate (the “ROIC Target”) set forth in the award agreements; and (ii) one-half of the target RSUs shall vest on the third fiscal year end date following the grant date, subject to INSW’s three-year total shareholder return (“TSR”) performance relative to that of a performance peer group over a three-year performance period (“TSR Target”). Vesting is subject in each case to the Human Resources and Compensation Committee of the Company’s Board of Directors’ certification of achievement of the performance measures and targets no later than March 15 th of the year following the vesting date. ​ In addition, in April 2019 and 2018 , the Company awarded an executive officer 11,882 performance-based restricted stock units, respectively, representing the second and third tranches of the award originally made on February 14, 2017. The grant date fair value of the performance award was determined to be $17.21 (2019) and $17.46 (2018) per RSU. Each performance stock unit represents a contingent right to receive RSUs based upon certain performance related goals being met and the covered employees being continuously employed through the end of the period over which the performance goals are measured. , respectively, was subject to INSW’s ROIC performance for the year ended December 31, 2019 and 2018, respectively, relative to a target rate set forth in the award agreement. ​ Settlement of the vested INSW performance-based RSUs may be in either shares of common stock or cash, as determined by the Human Resources and Compensation Committee in its discretion, and shall occur as soon as practicable after the vesting date. ​ (ii) Stock Options ​ During the years ended December 31, 2020, 2019 and 2018, the Company awarded to certain senior officers an aggregate of 131,992, 137,847 and 124,955 stock options, respectively. Each stock option represents an option to purchase one share of INSW common stock for an exercise price of $21.93 , period of time ending on the earlier to occur of (i) the 90 ​ Dividends ​ On February 26, 2020 , May 20, 2020 , August 4, 2020 , and October 28, 2020 , respectively, the Company’s Board of Directors declared regular quarterly cash dividends of $0.06 per share. Pursuant to these declarations, the Company made dividend payments totaling $1.7 million on each of March 30, 2020, June 22, 2020, September 23, 2020, and December 23, 2020, respectively, to stockholders of record as of March 17, 2020 , June 8, 2020 , September 9, 2020 , and December 8, 2020 , respectively. The Company’s Board of Directors declared a regular quarterly cash dividend of $0.06 per share of common stock on February 23, 2021 . The dividend will be paid on March 26, 2021 to shareholders of record at the close of business on March 11, 2021 . ​ Share Repurchases ​ In connection with the settlement of vested restricted stock units, the Company repurchased 75,894, 21,589 and 28,002 shares of common stock during the years ended December 31, 2020, 2019 and 2018 at an average cost of $20.31, $17.07 and $17.81 per share, respectively (based on the market prices on the dates of vesting), from employees, including certain members of management to cover withholding taxes. ​ On March 5, 2019 24-month ending March 5, 2021 During the first half of 2020, the Company repurchased and retired 1,417,292 shares of its common stock in open-market purchases, at an average price of $21.16 per share, for a total cost of $30.0 million. On August 4, 2020, the Company’s Board of Directors authorized the renewal of the share repurchase program in the amount of $30.0 million for another 24-month period ending August 4, 2022 . Subsequently, on October 28, 2020, the Company’s Board of Directors authorized an increase in the share repurchase program from $30.0 million to $50.0 million. No shares were acquired under repurchase programs during the second half of 2020 nor ​ Activity with respect to restricted common stock and restricted stock units under INSW compensation plans is summarized as follows: ​ ​ ​ ​ ​ ​ Common Stock Nonvested Shares Outstanding at December 31, 2017 ​ 174,177 Granted (2) ​ 173,573 Forfeitures (3) ​ (19,995) Vested ($18.62 - $24.05 per share) (1) ​ (97,554) Nonvested Shares Outstanding at December 31, 2018 ​ 230,201 Granted (2) ​ 270,096 Forfeitures (3) ​ (20,570) Vested ($17.46- $29.61 per share) (1) ​ (126,863) Nonvested Shares Outstanding at December 31, 2019 ​ 352,864 Granted (2) ​ 182,142 Forfeitures (3) ​ — Vested ($17.21- $27.66 per share) (1) ​ (229,123) Nonvested Shares Outstanding at December 31, 2020 ​ 305,883 (1) Includes 71,513 (2020), 21,529 (2019) and 21,752 (2018) shares of common stock sold back to the Company by employees to cover withholding taxes in the year of vesting or during the first quarter of the subsequent year. (2) Includes 8,309 , 8,198 and 3,120 incremental performance restricted stock units earned as a result of above target achievement of market condition at December 31, 2020, 2019 and 2018, respectively. (3) Represents restricted stock units forfeited because performance targets were not achieved as of the measurement date. ​ ​ Activity with respect to stock options under INSW compensation plans is summarized as follows: ​ ​ ​ ​ ​ ​ Common Stock Options Outstanding at December 31, 2017 ​ 275,830 Granted ​ 124,955 Exercised ​ — Options Outstanding at December 31, 2018 ​ 400,785 Granted ​ 137,847 Exercised ​ — Options Outstanding at December 31, 2019 ​ 538,632 Granted ​ 131,992 Exercised ​ — Options Outstanding at December 31, 2020 ​ 670,624 Options Exercisable at December 31, 2020 ​ 405,082 ​ The weighted average remaining contractual life of the outstanding and exercisable stock options at December 31, 2020 was 7.15 years and 6.20 years, respectively. The range of exercise prices of the stock options outstanding and exercisable at December 31, 2020 was between $17.21 and $30.93 per share, respectively. The weighted average exercise price of the stock options outstanding and exercisable at December 31, 2020 was $19.78 and $19.90, respectively. The aggregate intrinsic value of the INSW stock options outstanding and exercisable at December 31, 2020 was nil, respectively. ​ Compensation expense is recognized over the vesting period applicable to each grant, using the straight-line method. ​ Compensation expense with respect to restricted common stock and restricted stock units outstanding for the years ended December 31, 2020, 2019 and 2018 was $4.6 million, $3.2 million and $2.3 million, respectively. Compensation expense relating to stock options for the years ended December 31, 2020, 2019 and 2018 was $1.1 million, $1.1 million and $0.9 million, respectively. ​ As of December 31, 2020, there was $4.8 million of unrecognized compensation cost related to INSW nonvested share-based compensation arrangements. That cost is expected to be recognized over a weighted average period of 1.65 years.

ACCUMULATED OTHER COMPREHENSIVE

ACCUMULATED OTHER COMPREHENSIVE LOSS	12 Months Ended
	Dec. 31, 2020
ACCUMULATED OTHER COMPREHENSIVE LOSS [Abstract]
ACCUMULATED OTHER COMPREHENSIVE LOSS	NOTE 13 —ACCUMULATED OTHER COMPREHENSIVE LOSS: The components of accumulated other comprehensive loss, net of related taxes, in the consolidated balance sheets follow: ​ ​ ​ ​ ​ ​ ​ (Dollars in thousands) ​ December 31, 2020 ​ December 31, 2019 Unrealized losses on derivative instruments ​ $ (24,098) ​ $ (11,732) Items not yet recognized as a component of net periodic benefit cost (pension plans) ​ ​ (8,515) ​ ​ (8,838) ​ ​ $ (32,613) ​ $ (20,570) ​ The following tables present the changes in the balances of each component of accumulated other comprehensive loss, net of related taxes, for the three years ended December 31, 2020. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (Dollars in thousands) ​ Unrealized losses on cash flow hedges ​ Items not yet recognized as a component of net periodic benefit cost (pension plans) ​ Total Balance at December 31, 2017 ​ $ (28,989) ​ $ (11,418) ​ $ (40,407) Current period change, excluding amounts reclassified from accumulated other comprehensive loss ​ ​ (1,687) ​ ​ 1,107 ​ ​ (580) Amounts reclassified from accumulated other comprehensive loss ​ ​ 9,156 ​ ​ 1,902 ​ ​ 11,058 Balance at December 31, 2018 ​ ​ (21,520) ​ ​ (8,409) ​ ​ (29,929) Current period change, excluding amounts reclassified from accumulated other comprehensive loss ​ ​ (19,126) ​ ​ (818) ​ ​ (19,944) Amounts reclassified from accumulated other comprehensive loss ​ ​ 28,914 ​ ​ 389 ​ ​ 29,303 Balance at December 31, 2019 ​ ​ (11,732) ​ $ (8,838) ​ ​ (20,570) Current period change, excluding amounts reclassified from accumulated other comprehensive loss ​ ​ (21,503) ​ ​ (61) ​ ​ (21,564) Amounts reclassified from accumulated other comprehensive loss ​ ​ 9,137 ​ ​ 384 ​ ​ 9,521 Balance at December 31, 2020 ​ $ (24,098) ​ $ (8,515) ​ $ (32,613) ​ The following table presents information with respect to amounts reclassified out of accumulated other comprehensive loss for the three years ended December 31, 2020. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (Dollars in thousands) ​ ​ 2020 ​ ​ 2019 ​ ​ 2018 ​ Statement of Operations Reclassifications of losses on cash flow hedges: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Interest rate swaps entered into by the Company's equity method ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Equity in income of joint venture investees ​ $ 1,109 ​ $ 26,490 ​ $ 8,664 ​ affiliated companies Interest rate swaps entered into by the Company's subsidiaries ​ ​ 4,571 ​ ​ 1,467 ​ ​ 471 ​ Interest expense Interest rate cap/collar entered into by the Company's subsidiaries ​ ​ — ​ ​ 99 ​ ​ 21 ​ Interest expense ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Reclassifications of losses on derivatives subsequent to ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ discontinuation of hedge accounting ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Interest rate collar entered into by the Company's subsidiaries ​ ​ 81 ​ ​ 858 ​ ​ — ​ Interest expense ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Reclassifications of losses on other-than-insignificant financing ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ element of derivatives: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Interest rate swaps entered into by the Company's subsidiaries ​ ​ 3,376 ​ ​ — ​ ​ — ​ Interest expense ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Items not yet recognized as a component of net periodic benefit cost ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (pension plans): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net periodic benefit costs associated with pension and ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ postretirement benefit plans ​ ​ 384 ​ ​ 389 ​ ​ 1,902 ​ Other expense Total before and net of tax ​ $ 9,521 ​ $ 29,303 ​ $ 11,058 ​ ​ ​ The following amounts are included in accumulated other comprehensive loss at December 31, 2020, which have not yet been recognized in net periodic cost: unrecognized prior service costs of $1.4 million ($1.0 million net of tax) and unrecognized actuarial losses of $8.9 million ($7.5 million net of tax). ​ At December 31, 2020, the Company expects that it will reclassify $9.6 million (gross and net of tax) of net losses on derivative instruments from accumulated other comprehensive loss to earnings during the next twelve months due to the payment of variable rate interest associated with floating rate debt of INSW’s equity method investees and the interest rate collar and swaps held by the Company. See Note 6, “Equity Method Investments,” for additional information relating to derivatives held by the Company’s equity method investees and Note 9, “Fair Value of Financial Instruments, Derivatives and Fair Value,” for additional disclosures relating to derivative instruments.

REVENUE

REVENUE	12 Months Ended
	Dec. 31, 2020
REVENUE [Abstract]
REVENUE	NOTE 14 — REVENUE: Revenue Recognition The majority of the Company's contracts for pool revenues, time and bareboat charter revenues, and voyage charter revenues are accounted for as lease revenue under ASC 842. The Company's contracts with pools are cancellable with up to 90 days' notice. As of December 31, 2020, the Company is a party to time charter out contracts with customers on six Panamaxes (including one which was delivered to the charterer in early January 2021), one LR2, and two VLCCs with expiry dates ranging from February 2021 to March 2023. Upon their expiry in February 2021, the Company extended the time charters on two Panamaxes for an additional three months through May 2021. The Company is also a party to a one-year profit share agreement, which expires in March 2021, to participate in 25% of the profits and losses generated from a chartered-in MR commercially managed by a pool in which the Company participates. The Company’s share of earnings and charter hire expenses from this profit share agreement are included in voyage charter revenues and charter hire expenses, respectively, in the accompanying consolidated statements of operations. Lightering services provided by the Company's Crude Tanker Lightering Business and voyage charter contracts that do not meet the definition of a lease are accounted for as service revenues under ASC 606. In accordance with ASC 606, revenue is recognized when a customer obtains control of or consumes promised services. The amount of revenue recognized reflects the consideration to which the Company expects to be entitled to receive in exchange for these services. See Note 2, “Significant Accounting Policies,” for additional detail on the Company’s accounting policies regarding service revenue recognition and costs to obtain or fulfill a contract. ​ ​ The following table presents the Company’s revenues from leases accounted for under ASC 842 and revenues from services accounted for under ASC 606 for the years ended December 31, 2020, 2019 and 2018: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Crude ​ Product ​ ​ ​ ​ ​ ​ (Dollars in thousands) ​ Tankers ​ Carriers ​ Other ​ Totals 2020 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Revenues from leases ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Pool revenues ​ $ 198,316 ​ $ 74,664 ​ $ — ​ $ 272,980 Time and bareboat charter revenues ​ ​ 87,783 ​ ​ 936 ​ ​ — ​ ​ 88,719 Voyage charter revenues from non-variable lease payments (1) ​ ​ 19,016 ​ ​ 10,456 ​ ​ — ​ ​ 29,472 Voyage charter revenues from variable lease payments ​ ​ 1,180 ​ ​ 827 ​ ​ — ​ ​ 2,007 Revenues from services ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Voyage charter revenues ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Service revenue from voyage charters ​ ​ 472 ​ ​ — ​ ​ — ​ ​ 472 Lightering services ​ ​ 27,998 ​ ​ — ​ ​ — ​ ​ 27,998 Total shipping revenues ​ $ 334,765 ​ $ 86,883 ​ $ — ​ $ 421,648 2019 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Revenues from leases ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Pool revenues ​ $ 173,751 ​ $ 80,304 ​ $ — ​ $ 254,055 Time and bareboat charter revenues ​ ​ 27,535 ​ ​ 90 ​ ​ — ​ ​ 27,625 Voyage charter revenues from non-variable lease payments (1) ​ ​ 29,786 ​ ​ 434 ​ ​ — ​ ​ 30,220 Voyage charter revenues from variable lease payments ​ ​ 2,574 ​ ​ — ​ ​ — ​ ​ 2,574 Revenues from services ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Voyage charter revenues ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Lightering services ​ ​ 51,710 ​ ​ — ​ ​ — ​ ​ 51,710 Total shipping revenues ​ $ 285,356 ​ $ 80,828 ​ $ — ​ $ 366,184 2018 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Revenues from leases ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Pool revenues ​ $ 111,214 ​ $ 65,992 ​ $ — ​ $ 177,206 Time and bareboat charter revenues ​ ​ 24,088 ​ ​ 1,873 ​ ​ — ​ ​ 25,961 Voyage charter revenues from non-variable lease payments (1) ​ ​ 20,682 ​ ​ 100 ​ ​ — ​ ​ 20,782 Voyage charter revenues from variable lease payments ​ ​ 1,346 ​ ​ — ​ ​ — ​ ​ 1,346 Revenues from services ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Voyage charter revenues ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Lightering services ​ ​ 45,066 ​ ​ — ​ ​ — ​ ​ 45,066 Total shipping revenues ​ $ 202,396 ​ $ 67,965 ​ $ — ​ $ 270,361 (1) Includes $4.4 million, $0.3 million and $2.3 million of loss of hire insurance proceeds received during the years ended December 31, 2020, 2019 and 2018, respectively. All such proceeds were associated with vessels in our Crude Tankers segment except for the 2019 proceeds which was associated with a vessel in the Product Carriers segment. ​ ​ Contract Balances ​ The following table provides information about receivables, contract assets and contract liabilities from contracts with customers, and significant changes in contract assets and liabilities balances, associated with revenue from services accounted for under ASC 606. Balances related to revenues from leases accounted for under ASC 842 are excluded from the table below. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (Dollars in thousands) ​ Voyage receivables - Billed receivables ​ Contract assets (Unbilled voyage receivables) ​ Contract liabilities (Deferred revenues and off hires) Opening balance as of January 1, 2020 ​ $ 2,727 ​ $ — ​ $ — Closing balance as of December 31, 2020 ​ ​ 2,148 ​ ​ 166 ​ ​ — ​ We receive payments from customers based on the distribution schedule established in our contracts. Contract assets relate to our conditional right to consideration for our completed performance under contracts and decrease when the right to consideration becomes unconditional or payments are received. Contract liabilities include payments received in advance of performance under contracts and are recognized when performance under the respective contract has been completed. Deferred revenues allocated to unsatisfied performance obligations will be recognized over time as the services are performed. ​ Performance Obligations ​ All of the Company's performance obligations, and associated revenue, are generally transferred to customers over time. The expected duration of services is less than one year. Positive/(negative) adjustments to revenues from performance obligations satisfied in previous periods recognized during the years ended December 31, 2020 and 2019 were $47 thousand and ($493) thousand, respectively. These adjustments to revenue were related to changes in estimates of performance obligations related to voyage charters. ​ Costs to Obtain or Fulfill a Contract ​ As of December 31, 2020, there were no unamortized deferred costs of obtaining or fulfilling a contract.

LEASES

LEASES	12 Months Ended
	Dec. 31, 2020
LEASES [Abstract]
LEASES	NOTE 15 — LEASES: As permitted under ASC 842, the Company has elected not to apply the provisions of ASC 842 to short term leases, which include: (i) tanker vessels chartered-in where the duration of the charter was one year or less at inception; (ii) workboats employed in the Crude Tankers Lightering business which are cancellable upon 180 days ' notice; and (iii) short term leases of office and other space. ​ Contracts under which the Company is a Lessee The Company currently has two major categories of leases - chartered-in vessels and leased office and other space. The expenses recognized during the years ended December 31, 2020 and 2019 for the lease component of these leases are as follows: ​ ​ ​ ​ ​ ​ ​ ​ (Dollars in thousands) ​ ​ 2020 ​ ​ 2019 Operating lease cost ​ ​ ​ ​ ​ ​ Vessel assets ​ ​ ​ ​ ​ ​ Charter hire expenses ​ $ 11,666 ​ $ 15,089 ​ ​ ​ ​ ​ ​ ​ Office and other space ​ ​ ​ ​ ​ ​ General and administrative ​ ​ 1,044 ​ ​ 996 Voyage expenses ​ ​ 168 ​ ​ 168 ​ ​ ​ ​ ​ ​ ​ Short-term lease cost ​ ​ ​ ​ ​ ​ Vessel assets (1) ​ ​ ​ ​ ​ ​ Charter hire expenses ​ ​ 4,585 ​ ​ 10,769 ​ ​ ​ ​ ​ ​ ​ Office and other space ​ ​ ​ ​ ​ ​ General and administrative ​ ​ 29 ​ ​ 116 Voyage expenses ​ ​ — ​ ​ 52 Vessel expenses ​ ​ — ​ ​ 8 Total lease cost ​ $ 17,492 ​ $ 27,198 (1) Excludes vessels spot chartered-in under operating leases and employed in the Crude Tankers Lightering business for periods of less than one month each, totaling $1.2 million and $10.6 million for the years ended December 31, 2020 and 2019, respectively, including both lease and non-lease components. ​ ​ Supplemental cash flow information related to leases was as follows: ​ ​ ​ ​ ​ ​ ​ ​ (Dollars in thousands) ​ ​ 2020 ​ ​ 2019 Cash paid for amounts included in the measurement of lease liabilities ​ ​ ​ ​ ​ ​ Operating cash flows used for operating leases ​ $ 12,878 ​ $ 16,178 ​ Supplemental balance sheet information related to leases was as follows: ​ ​ ​ ​ ​ ​ ​ ​ (Dollars in thousands) ​ December 31, 2020 ​ December 31, 2019 Operating lease right-of-use assets ​ $ 21,588 ​ $ 33,718 ​ ​ ​ ​ ​ ​ ​ Current portion of operating lease liabilities ​ $ (8,867) ​ $ (12,958) Long-term operating lease liabilities ​ ​ (10,253) ​ ​ (17,953) Total operating lease liabilities ​ $ (19,120) ​ $ (30,911) ​ ​ ​ ​ ​ ​ ​ Weighted average remaining lease term - operating leases ​ ​ 2.75 years ​ ​ 3.24 years Weighted average discount rate - operating leases ​ ​ 7.21% ​ ​ 7.16% ​ 1. Charters-in of vessel assets: ​ During March 2020, two 2007-built MRs time chartered-in by the Company were arrested by a third party due to a legal dispute between said party and the ultimate owners of the vessels. As a result of the arrests, the entity that chartered these vessels to INSW was no longer able to perform its obligations under the time charter agreements and effectively terminated the time charter agreements. Accordingly, the Company derecognized lease liabilities and right of use assets associated with these agreements ​ As of December 31, 2020, INSW had commitments to charter in two Aframaxes, one LR1 and one workboat employed in the Crude Tankers Lightering business. All of the charters-in, of which the two Aframaxes are bareboat charters with expiry dates ranging from December 2023 to March 2024 and the others are time charters with expiry dates ranging from June 2021 to August 2021, are accounted for as operating leases. The Company’s bareboat charters contain purchase options commencing in the first quarter of 2021. As of December 31, 2020, the Company has determined that the purchase options are not reasonably certain of being exercised. Lease liabilities related to time charters-in vessels exclude estimated days that the vessels will not be available for employment due to drydock because the Company does not pay charter hire when time chartered-in vessels are not available for its use ​ Payments of lease liabilities and related number of operating days under these operating leases as of December 31, 2020 are as follows ​ Bareboat Charters-in ​ ​ ​ ​ ​ ​ (Dollars in thousands) ​ Amount ​ Operating Days 2021 ​ $ 6,278 ​ 730 2022 ​ ​ 6,278 ​ 730 2023 ​ ​ 4,532 ​ 556 Total lease payments ​ ​ 17,088 ​ 2,016 less imputed interest ​ ​ (1,608) ​ ​ Total operating lease liabilities ​ $ 15,480 ​ ​ ​ Time Charters-in ​ ​ ​ ​ ​ ​ (Dollars in thousands) ​ Amount ​ Operating Days 2021 ​ $ 2,170 ​ 408 Total lease payments (lease component only) ​ ​ 2,170 ​ 408 less imputed interest ​ ​ (43) ​ ​ Total operating lease liabilities ​ $ 2,127 ​ ​ ​ ​ 2. Office and other space: ​ The Company has operating leases for office and lightering workboat dock space. These leases have expiry dates ranging from August 2021 to December 2024. The lease for the workboat dock space contains renewal options executable by the Company for periods through December 2027. We have determined that the options through December 2024 are reasonably certain to be executed by the Company, and accordingly are included in the lease liability and right of use asset calculations for such lease. ​ Payments of lease liabilities for office and other space as of December 31, 2020 are as follows: ​ ​ ​ ​ ​ (Dollars in thousands) ​ ​ Amount 2021 ​ $ 936 2022 ​ ​ 273 2023 ​ ​ 229 2024 ​ ​ 178 Total lease payments ​ ​ 1,616 less imputed interest ​ ​ (103) Total operating lease liabilities ​ $ 1,513 ​ Contracts under which the Company is a Lessor ​ See Note 14, “Revenue,” for discussion on the Company’s revenues from operating leases accounted for under ASC 842. The future minimum revenues, before reduction for brokerage commissions, expected to be received on non-cancelable time charters for six Panamaxes, one LR2 and two VLCCs and the related revenue days as of December 31, 2020 are as follows: ​ ​ ​ ​ ​ ​ ​ (Dollars in thousands) ​ Amount ​ Revenue Days 2021 ​ $ 28,856 ​ 1,053 2022 ​ ​ 16,425 ​ 365 2023 ​ ​ 3,195 ​ 71 Future minimum revenues ​ $ 48,476 ​ 1,489 ​ Future minimum revenues do not include (i) the Company’s share of time charters entered into by the pools in which it participates, and (ii) the Company’s share of time charters entered into by the joint ventures, which the Company accounts for under the equity method. Revenues from a time charter are not generally received when a vessel is off-hire, including time required for normal periodic maintenance of the vessel. In arriving at the minimum future charter revenues, an estimated time off-hire to perform periodic maintenance on each vessel has been deducted, although there is no assurance that such estimate will be reflective of the actual off-hire in the future.

PENSION AND OTHER POSTRETIREMEN

PENSION AND OTHER POSTRETIREMENT BENEFIT PLANS	12 Months Ended
	Dec. 31, 2020
Pension and Other Postretirement Benefit Plans [Abstract]
Pension and Other Postretirement Benefit Plans	NOTE 16 —PENSION AND OTHER POSTRETIREMENT BENEFIT PLANS: ​ Pension plans ​ The Company has obligations outstanding under a defined benefit pension plan in the U.K. The plan provides defined benefits based on years of service and final average salary. The plan was closed to new entrants and accrual from June 2014. The Company has provided a guarantee to the trustees of the OSG Ship Management (UK) Ltd. Retirement Benefits Plan (the “Scheme”) in the amount of the unfunded deficiency calculated on a solvency basis, if the principal employer fails to make the required periodic contributions to the Scheme. ​ Information with respect to the Scheme for which INSW uses a December 31 measurement date, is as follows: ​ ​ ​ ​ ​ ​ ​ ​ (Dollars in thousands) ​ December 31, 2020 ​ December 31, 2019 Change in benefit obligation: ​ ​ ​ ​ ​ ​ Benefit obligation at beginning of year ​ $ 27,481 ​ $ 23,814 Interest cost on benefit obligation ​ ​ 525 ​ ​ 657 Actuarial losses ​ ​ 2,202 ​ ​ 2,761 Benefits paid ​ ​ (875) ​ ​ (820) Foreign exchange losses ​ ​ 943 ​ ​ 1,069 Benefit obligation at year end ​ ​ 30,276 ​ ​ 27,481 ​ ​ ​ ​ ​ ​ ​ Change in plan assets: ​ ​ ​ ​ ​ ​ Fair value of plan assets at beginning of year ​ ​ 26,994 ​ ​ 22,785 Actual return on plan assets ​ ​ 3,427 ​ ​ 3,341 Employer contributions ​ ​ 664 ​ ​ 639 Benefits paid ​ ​ (875) ​ ​ (820) Foreign exchange gains ​ ​ 1,009 ​ ​ 1,049 Fair value of plan assets at year end ​ ​ 31,219 ​ ​ 26,994 Funded/(unfunded) status at December 31 ​ $ 943 ​ $ (487) ​ The funded or unfunded benefit obligation for the pension plan is included in other assets or other liabilities, respectively, in the accompanying consolidated balance sheets. ​ Information for net periodic benefit costs for the years ended December 31, 2020, 2019 and 2018 follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (Dollars in thousands) ​ ​ 2020 ​ ​ 2019 ​ ​ 2018 Components of expense: ​ ​ ​ ​ ​ ​ ​ ​ ​ Interest cost on benefit obligation ​ $ 525 ​ $ 657 ​ $ 707 Expected return on plan assets ​ ​ (1,018) ​ ​ (1,017) ​ ​ (1,029) Amortization of prior-service costs ​ ​ 75 ​ ​ 74 ​ ​ 71 Recognized net actuarial loss ​ ​ 310 ​ ​ 315 ​ ​ 388 Recognized settlement loss ​ ​ — ​ ​ — ​ ​ 1,442 Net periodic benefit cost ​ $ (108) ​ $ 29 ​ $ 1,579 ​ Unrecognized actuarial losses are amortized over a period of 19 years, which at the time selected, represented the term to retirement of the youngest member of the Scheme. ​ The weighted-average assumptions used to determine benefit obligations follow: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2020 ​ December 31, 2019 Discount rate ​ ​ 1.20% ​ ​ 2.00% ​ The selection of a single discount rate for the defined benefit plan was derived from bond yield curves, which the Company believed as of such dates to be appropriate for the plan, reflecting the length of the liabilities and the yields obtainable on investment grade bonds. The assumption for a long-term rate of return on assets was based on a weighted average of rates of return on the investment sectors in which the assets are invested. ​ The weighted-average assumptions used to determine net periodic benefit costs follow: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2020 ​ ​ 2019 ​ ​ 2018 Discount rate ​ ​ 2.00% ​ ​ 2.80% ​ ​ 2.40% Expected (long-term) return on plan assets ​ ​ 3.89% ​ ​ 4.46% ​ ​ 3.85% Rate of future compensation increases ​ ​ - ​ ​ - ​ ​ - ​ Expected benefit payments are as follows: ​ ​ ​ ​ ​ (Dollars in thousands) ​ Pension benefits 2021 ​ $ 865 2022 ​ ​ 866 2023 ​ ​ 895 2024 ​ ​ 1,022 2025 ​ ​ 1,126 Years 2026-2030 ​ ​ 5,452 ​ ​ $ 10,226 ​ The fair values of the Company’s pension plan assets at December 31, 2020, by asset category are as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (Dollars in thousands) ​ Fair Value ​ Level 1 ​ Level 2 (1) Cash and cash equivalents ​ $ 757 ​ $ 757 ​ $ — Managed funds ​ ​ 30,462 ​ ​ — ​ ​ 30,462 Total ​ $ 31,219 ​ $ 757 ​ $ 30,462 (1) Quoted prices for the managed funds are not available from an active market source since such investments are pooled investment funds. The unitized pooled investment vehicles have been valued at the latest available bid price or single price provided by the pooled investment manager. Shares in other pooled arrangements have been valued at the latest available net asset value, determined in accordance with fair value principles, provided by the pooled investment manager. ​ ​ A target allocation of 80% is maintained with return seeking assets, with the balance of 20% invested in liability driven investments to target a 100% match to interest rate risks by asset value (mainly government bonds). ​ The Company contributed $0.7 million, $0.6 million and $0 to the Scheme in 2020, 2019 and 2018, respectively. The Company expects that its contribution to the Scheme in 2021 will be approximately $0.7 million. ​ Defined Contribution Plans ​ The Company has defined contribution plans covering all eligible shore-based employees in the U.K. and U.S. Contributions are limited to amounts allowable for income tax purposes and include employer matching contributions to the plans. All contributions to the plans are at the discretion of the Company or as mandated by statutory laws. The employer matching contributions to the plans during each of the three years ended December 31, 2020 were $0.4 million.

OTHER EXPENSE

OTHER EXPENSE	12 Months Ended
	Dec. 31, 2020
OTHER EXPENSE [Abstract]
OTHER EXPENSE	NOTE 17 — OTHER EXPENSE: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (Dollars in thousands) ​ ​ 2020 ​ ​ 2019 ​ ​ 2018 Investment income - interest ​ $ 558 ​ $ 2,520 ​ $ 1,300 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net actuarial gain/(loss) on defined benefit pension plan ​ ​ 633 ​ ​ 628 ​ ​ (902) Write-off of deferred financing costs ​ ​ (13,073) ​ ​ (3,558) ​ ​ (2,400) Loss on extinguishment of debt ​ ​ (1,197) ​ ​ (1,100) ​ ​ (1,295) Other ​ ​ 262 ​ ​ 567 ​ ​ (418) ​ ​ $ (12,817) ​ $ (943) ​ $ (3,715) ​ Refer to Note 8, “Debt,” for additional information relating to write-off of deferred financing costs and loss on extinguishment of debt.

2020 AND 2019 QUARTERLY RESULTS

2020 AND 2019 QUARTERLY RESULTS OF OPERATIONS (UNAUDITED)	12 Months Ended
	Dec. 31, 2020
2020 AND 2019 QUARTERLY RESULTS OF OPERATIONS [Abstract]
2020 AND 2019 QUARTERLY RESULTS OF OPERATIONS (UNAUDITED)	NOTE 18 — 2020 AND 2019 QUARTERLY RESULTS OF OPERATIONS (UNAUDITED): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Selected Financial Data for the Quarter Ended ​ March 31, ​ June 30, ​ Sept. 30, ​ Dec. 31, 2020 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Shipping revenues ​ $ 125,337 ​ $ 139,725 ​ $ 99,883 ​ $ 56,703 Gain/(loss) on disposal of vessels and other property, including impairments (1) ​ ​ 2,804 ​ ​ (4,134) ​ ​ (12,834) ​ ​ (85,923) Income/(loss) from vessel operations ​ ​ 53,349 ​ ​ 67,892 ​ ​ 16,832 ​ ​ (98,193) Equity in income of affiliated companies (1) ​ ​ 5,111 ​ ​ 5,205 ​ ​ 5,356 ​ ​ (11,553) Interest expense ​ ​ (12,009) ​ ​ (8,881) ​ ​ (7,999) ​ ​ (7,823) Income tax provision ​ ​ — ​ ​ (1) ​ ​ — ​ ​ — Net income/(loss) ​ ​ 33,019 ​ ​ 64,358 ​ ​ 13,981 ​ ​ (116,889) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Basic and diluted net income/(loss) per share ​ $ 1.13 ​ $ 2.26 ​ $ 0.50 ​ $ (4.18) (1) Refer to Note 5, “Vessels, Deferred Drydock and Other Property” and Note 6, “Equity Method Investments,” respectively, for further information on a $85.9 million impairment charge recorded during the fourth quarter of 2020 and the Company’s $16.4 million share of a non-cash deferred tax provision recorded by the FSO Joint Venture during the fourth quarter of 2020. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Selected Financial Data for the Quarter Ended ​ March 31, ​ June 30, ​ Sept. 30, ​ Dec. 31, 2019 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Shipping revenues ​ $ 101,874 ​ $ 69,010 ​ $ 71,278 ​ $ 124,022 Gain/(loss) on disposal of vessels and other property ​ ​ 48 ​ ​ (1,548) ​ ​ 1,472 ​ ​ (280) Income/(loss) from vessel operations ​ ​ 19,324 ​ ​ (7,934) ​ ​ (2,843) ​ ​ 46,621 Equity in income of affiliated companies ​ ​ 8,070 ​ ​ 8,015 ​ ​ 8,474 ​ ​ (13,346) Interest expense ​ ​ (17,533) ​ ​ (17,443) ​ ​ (17,010) ​ ​ (14,281) Income tax provision ​ ​ — ​ ​ — ​ ​ — ​ ​ (1) Net income/(loss) ​ ​ 10,897 ​ ​ (16,523) ​ ​ (11,095) ​ ​ 15,891 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Basic and diluted net income/(loss) per share ​ $ 0.37 ​ $ (0.57) ​ $ (0.38) ​ $ 0.54 ​

CONTINGENCIES

CONTINGENCIES	12 Months Ended
	Dec. 31, 2020
CONTINGENCIES [Abstract]
CONTINGENCIES	NOTE 19 — CONTINGENCIES: ​ INSW’s policy for recording legal costs related to contingencies is to expense such legal costs as incurred. ​ Multi-Employer Plans ​ The Merchant Navy Officers Pension Fund (“MNOPF”) is a multi-employer defined benefit pension plan covering British crew members that served as officers on board INSW’s vessels (as well as vessels of other owners). The trustees of the plan have indicated that, under the terms of the High Court ruling in 2005, which established the liability of past employers to fund the deficit on the Post 1978 section of MNOPF, calls for further contributions may be required if additional actuarial deficits arise or if other employers liable for contributions are not able to pay their share in the future. As the amount of any such assessment cannot be reasonably estimated, no reserves have been recorded for this contingency in INSW’s consolidated financial statements as of December 31, 2020. The next deficit valuation will be as of March 31, 2021. The Merchant Navy Ratings Pension Fund (“MNRPF”) is a multi-employer defined benefit pension plan covering British crew members that served as ratings (seamen) on board INSW’s vessels (as well as vessels of other owners) more than 20 years ago. Participating employers include current employers, historic employers that have made voluntary contributions, and historic employers such as INSW that have made no deficit contributions. Calls for contributions may be required if additional actuarial deficits arise or if other employers liable for contributions are unable to pay their share in the future. As the amount of any such assessment cannot be reasonably estimated, no reserves have been recorded in INSW’s consolidated financial statements as of December 31, 2020. The next deficit valuation is as of March 31, 2020 with an actuarial valuation to be issued by June 30, 2021. ​ Galveston ​ In late September 2017, an industrial accident at a dock facility in Galveston, Texas resulted in fatalities to two temporary employees of a subsidiary of the Company, following which several legal matters ensued. First, the Occupational Safety and Health Administration and local law enforcement conducted accident investigations. These have not, to date, resulted in citations or other adverse enforcement actions being issued to and/or taken against the subsidiary. Second, two wrongful death lawsuits relating to the accident were filed in state court in Texas (Harris County District Court) in September 2017, identifying the subsidiary as one of several defendants; these lawsuits were subsequently settled in October 2017 as to most of the original defendants other than the subsidiary. In January 2018, the case was removed to federal district court in Houston, Texas (Southern District); after various court proceedings, the district court dismissed the remaining claims against the subsidiary with prejudice in May 2020. Third, several of the original defendants in the wrongful death/personal injury actions (the “T&T Defendants”) made demands to the subsidiary and its insurers for contractual defense, indemnity and additional insured coverage for all claims being asserted against them arising from the incident, including settlement amounts and defense costs. Following a series of proceedings that took place in 2017 and 2018 in federal and state courts in Texas and the U.S. Fifth Circuit Court of Appeals, in early 2019 the T&T Defendants settled their claims with the subsidiary and its insurers. Pursuant to the terms of that settlement, all litigation concerning these claims was dismissed with prejudice. Finally, in February 2018, the subsidiary and its insurers settled three “bystander” claims made by crew members aboard a nearby vessel that was under charter to the subsidiary for alleged emotional and other personal injuries. The subsidiary subsequently initiated an arbitration against the bystanders’ employer seeking recovery of the settlement payment. In August 2019, the arbitration panel issued a decision that provided for a partial recovery of costs, which was subsequently paid for the benefit of the subsidiary’s insurers. ​ Spin-Off Related Agreements On November 30, 2016, INSW was spun off from OSG as a separate publicly traded company. In connection with the spin-off, INSW and OSG entered into several agreements, including a separation and distribution agreement, an employee matters agreement and a transition services agreement. While most of the obligations under those agreements were subsequently fulfilled, certain provisions (including in particular mutual indemnification provisions under the separation and distribution agreement and the employee matters agreement) continue in force. Legal Proceedings Arising in the Ordinary Course of Business ​ The Company is a party, as plaintiff or defendant, to various suits in the ordinary course of business for monetary relief arising principally from personal injuries, wrongful death, collision or other casualty and to claims arising under charter parties and other contract disputes. A substantial majority of such personal injury, wrongful death, collision or other casualty claims against the Company are covered by insurance (subject to deductibles not material in amount). Each of the claims involves an amount which, in the opinion of management, should not be material to the Company’s financial position, results of operations and cash flows. ​

Subsequent Events

Subsequent Events	12 Months Ended
	Dec. 31, 2020
Subsequent Events [Abstract]
Subsequent Events	NOTE 20 — SUBSEQUENT EVENTS: On March 11, 2021, the Company entered into agreements to construct three dual-fuel LNG VLCCs at Daewoo Shipbuilding and Marine Engineering’s shipyard, subject to certain conditions customary to similar transactions. The VLCCs will be able to burn LNG in their power plant, which will significantly reduce greenhouse gas emissions. Upon delivery to the Company in 2023, the vessels will be employed on seven-year time charter contracts with oil major – Shell. The total construction cost for the vessels will be approximately $290 million, which will be paid for through a combination of long-term financing and available liquidity. ​

SIGNIFICANT ACCOUNTING POLICIES

SIGNIFICANT ACCOUNTING POLICIES (Policies)	12 Months Ended
	Dec. 31, 2020
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES [Abstract]
Cash, cash equivalents and Restricted cash	1. Cash and cash equivalents —
Concentration of Credit Risk	2. Concentration of credit risk Leases Revenue from Contracts with Customers ​ With respect to non-operating lease receivables, the Company recognizes as an allowance its estimate of expected credit losses in accordance with ASC 326, Financial Instruments – Credit losses of the counterparty, and their business strategy. We manage our non-operating lease receivable portfolios using delinquency as a key credit quality indicator. The Company performs the following steps in estimating expected losses: (i) gather historical losses over 5 years; (ii) assume outstanding billed amounts over 180 days as additional expected losses; and (iii) make forward-looking adjustments to the expected losses to reflect future economic conditions by comparing credit default swap rates of significant customers over time. In addition, the Company performs individual assessments for customers that do not share risk characteristics with other customers (for example a customer under bankruptcy or a customer with known disputes or collectability issues). ​ The allowance for credit losses is recognized as an allowance or contra-asset and reflects our best estimate of probable losses inherent in the voyage receivables balance. Provisions for credit losses associated with voyage receivables are included in provision for credit losses on the consolidated statements of operations. Activity for allowance for credit losses is summarized as follows: ​ ​ ​ ​ ​ (Dollars in thousands) ​ ​ Allowance for Credit Losses - Voyage Receivables Balance at January 1, 2018 ​ $ — Provision for expected credit losses ​ ​ — Balance at December 31, 2018 ​ ​ — Provision for expected credit losses ​ ​ 1,245 Balance at December 31, 2019 ​ ​ 1,245 Provision for expected credit losses ​ ​ 58 Write-offs charged against the allowance ​ ​ (1,119) Recoveries of amounts previously written off ​ ​ (129) Balance at December 31, 2020 ​ $ 55 ​ We are also exposed to credit losses from off-balance sheet exposures related to guarantees of joint venture debt. See Note 6, “Equity Method Investments,” for more information on these off-balance sheet exposures. ​ During the year ended December 31, 2020, 2019 and 2018, the Company did not have any individual customers who accounted for 10% or more of its revenues apart from the pools in which it participates. The pools in which the Company participates accounted in aggregate 88% of consolidated voyage receivables at December 31, 2020 and December 31, 2019, respectively.
Inventories	3. Inventories
Vessels, vessel lives, deferred drydocking expenditures and other property	4. Vessels, vessel lives, deferred drydocking expenditures and other property ​ Interest costs are capitalized to vessels during the period that vessels are under construction. No interest was capitalized during the three years ended December 31, 2020, since the Company had no vessels under construction during this period. ​ Other property, including leasehold improvements, are recorded at cost and amortized on a straight-line basis over the shorter of the terms of the leases or the estimated useful lives of the assets, which range from three ​ Expenditures incurred during a drydocking are deferred and amortized on the straight-line basis over the period until the next scheduled drydocking, which is generally two
Impairment of long-lived assets	5. Impairment of long-lived assets
Deferred finance charges	6. Deferred finance charges Finance charges, excluding original issue discount, incurred in the arrangement and/or amendments resulting in the modification of debt are deferred and amortized to interest expense on either an effective interest method or straight-line basis over the life of the related debt ​ Interest expense relating to the amortization of deferred financing costs amounted to $2.8 million in 2020, $4.8 million in 2019 and $3.9 million in 2018.
Revenue and expense recognition	7. Revenue and expense recognition ​ Under ASC 842, lease revenue for fixed lease payments is recognized over the lease term on a straight-line basis and lease revenue for variable lease payments (e.g., demurrage) are recognized in the period in which the changes in facts and circumstances on which the variable lease payments are based occur. Initial direct costs are expensed over the lease term on the same basis as lease revenue. The Company has elected the lessor practical expedient to aggregate non-lease components with the associated lease components and to account for the combined components as required by the practical expedient since its primary revenue streams described above meet the conditions required to adopt the practical expedient. Furthermore, the Company has performed a qualitative analysis of each of its primary revenue contract types to determine whether the lease component or the non-lease component is the predominant component of the contract. The Company concluded that the lease component is the predominant component for all of its primary revenue contract types, as the lessee would ascribe more value to the control and use of the underlying vessel rather than to the technical services to operate the vessel which is an add-on service to the lessee. ​ Revenues from time charters are accounted for as fixed rate operating leases with an embedded technical management service component and are recognized ratably over the rental periods of such charters. Bareboat charters are also accounted for as fixed rate operating leases and the associated revenue is recognized ratably over the rental periods of such charters. Voyage charters contain a lease component if the contract (i) specifies a specific vessel asset; and (ii) has terms that allow the charterer to exercise substantive decision-making rights, which have an economic value to the charterer and therefore allow the charterer to direct how and for what purpose the vessel is used. Voyage charter revenues and expenses are recognized ratably over the estimated length of each voyage. For a voyage charter which contains a lease component, revenue and expenses are recognized based on a lease commencement-to-discharge basis and the lease commencement date is the latter of discharge of the previous cargo or voyage charter contract signing. For voyage charters that do not have a lease component, revenue and expenses are recognized based on a load-to-discharge basis. Accordingly, voyage expenses incurred during a vessel’s positioning voyage to a load port in order to serve a customer under a voyage charter not containing a lease are considered costs to fulfill a contract and are deferred and recognized ratably over the load-to-discharge portion of the contract. ​ Under voyage charters, expenses such as fuel, port charges, canal tolls, cargo handling operations and brokerage commissions are paid by the Company whereas, under time and bareboat charters, such voyage costs are paid by the Company’s customers. ​ For the Company’s vessels operating in pools, revenues and voyage expenses are pooled and allocated to each pool’s participants on a time charter equivalent (“TCE”) basis in accordance with an agreed-upon formula. Accordingly, the Company accounts for its agreements with commercial pools as variable rate operating leases. For the pools in which the Company participates, management monitors, among other things, the relative proportion of the Company’s vessels operating in each of the pools to the total number of vessels in each of the respective pools and assesses whether or not the Company’s participation interest in each of the pools is sufficiently significant so as to determine that the Company has effective control of the pool. ​ Demurrage earned during a voyage charter represents variable consideration. The Company estimates demurrage at contract inception using either the expected value or most likely amount approaches. Such estimate is reviewed and updated over the term of the voyage charter contract. ​ The Company recognizes revenues from services in accordance with the provisions of ASC 606. The standard provides a unified model to determine how revenue is recognized. In doing so, the Company makes judgments including identifying performance obligations in the contract, estimating the amount of variable consideration to include in the transaction price, and allocating the transaction price to each performance obligation. Revenues are recognized to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. In determining the appropriate amount of revenue to be recognized as it fulfills its obligations under its agreements, the Company performs the following steps: (i) identification of the promised goods or services in the contract; (ii) determination of whether the promised goods or services are performance obligations, including whether they are distinct in the context of the contract; (iii) measurement of the transaction price, including the constraint on variable consideration; (iv) allocation of the transaction price to the performance obligations based on estimated selling prices; and (v) recognition of revenue when (or as) the Company satisfies each performance obligation. ​ As the Company’s performance obligations are services which are received and consumed by its customers as it performs such services, revenues are recognized over time proportionate to the days elapsed since the service commencement compared to the total days anticipated to complete the service. The minimum duration of services is less than one year for each of the Company’s current contracts.
Leases	8. Leases — The Company determines if an arrangement is a lease at inception. Operating leases are included in operating lease right-of-use (“ROU”) assets, current portion of operating lease liabilities, and long-term operating lease liabilities in the Company’s consolidated balance sheets. The Company does not have finance leases. ​ ROU assets represent our right to use an underlying asset for the lease term and lease liabilities represent our obligation to make lease payments arising from the lease. Operating lease ROU assets and liabilities are recognized at commencement date based on the present value of lease payments over the lease term. The operating lease ROU asset also includes any prepaid lease payments made and excludes accrued lease payments and lease incentives. Our lease terms take into consideration options to extend or terminate the lease, or purchase the underlying asset when it is reasonably certain that we will exercise such options. Lease expense for lease payments is recognized on a straight-line basis over the lease term. As most of our leases do not provide an implicit rate, we use our incremental borrowing rate based on the information available at commencement date in determining the present value of lease payments. The Company makes significant judgements and assumptions to estimate its incremental borrowing rate that a lessee would have to pay to borrow on a 100% collateralized basis over a term similar to the lease term and in an amount equal to the lease payments in a similar economic environment. The Company performs the following steps in estimating its incremental borrowing rate: (i) gather observable debt yields of the Company’s recently issued debt facilities; and (ii) make adjustments to the yields of the actual debt facilities to reflect changes in collateral level, terms, the risk-free interest rate, and credit ratings. In addition, the Company performs sensitivity analyses to evaluate the impact of selected discount rates on the estimated lease liability. The Company makes significant judgements and assumptions to separate the lease component from the non-lease component of its time chartered-in vessels. For purposes of determining the standalone selling price of the vessel lease and technical management service components of the Company’s time charters, the Company concluded that the residual approach would be the most appropriate method to use given that vessel lease rates are highly variable depending on shipping market conditions, the duration of such charters, and the age of the vessel. The Company believes that the standalone transaction price attributable to the technical management service component is more readily determinable than the price of the lease component and, accordingly, the price of the service component is estimated using observable data (such as fees charged by third-party technical managers) and the residual transaction price is attributed to the vessel lease component.
Derivatives	9. Derivatives — Derivatives and Hedging ​ The Company formally documents all relationships between hedging instruments and hedged items, as well as its risk-management objective and strategy for undertaking various hedge transactions. This process includes linking all derivatives that are designated as cash flow hedges to forecasted transactions. The Company also formally assesses (both at the hedge’s inception and on an ongoing basis) whether the derivatives that are used in hedging transactions have been highly effective in offsetting changes in the cash flows of hedged items and whether those derivatives may be expected to remain highly effective in future periods. When it is determined that a derivative is not (or has ceased to be) highly effective as a hedge, the Company discontinues hedge accounting prospectively, as discussed below. ​ The Company discontinues hedge accounting prospectively when: (1) it determines that the derivative is no longer effective in offsetting changes in the cash flows of a hedged item such as forecasted transactions; (2) the derivative expires or is sold, terminated, or exercised; (3) it is no longer probable that the forecasted transaction will occur; or (4) management determines that designating the derivative as a hedging instrument is no longer appropriate or desired. ​ When the Company discontinues hedge accounting because it is no longer probable that the forecasted transaction will occur in the originally expected period, the gain or loss on the derivative remains in accumulated other comprehensive income/(loss) and is reclassified into earnings when the forecasted transaction affects earnings. However, if it is probable that a forecasted transaction will not occur by the end of the originally specified time period or within an additional two-month period of time thereafter, the gains and losses that were accumulated in other comprehensive gain/(loss) will be recognized immediately in earnings. In all situations in which hedge accounting is discontinued and the derivative remains outstanding, the Company will carry the derivative at its fair value on the consolidated balance sheets, recognizing changes in the fair value in current-period earnings, unless it is designated in a new hedging relationship. ​ Any gain or loss realized upon the early termination of an interest rate cap, collar or swaps is recognized as an adjustment of interest expense over the shorter of the remaining term of the derivative instruments or the hedged debt. See Note 9, “Fair Value of Financial Instruments, Derivatives and Fair Value Disclosures,” for additional disclosures on the Company’s interest rate cap, collar and swaps and other financial instruments.
Fair value measurements	10. Fair value measurements — Fair Value Measurement fair value of assets and liabilities should include consideration of non-performance risk, which for the liabilities described below includes the Company's own credit risk. The hierarchy below lists three levels of fair value based on the extent to which inputs used in measuring fair value are observable in the market: ​ Level 1 - Quoted prices in active markets for identical assets or liabilities. Our Level 1 non-derivative assets and liabilities primarily include cash and cash equivalents and the 8.50% Senior Notes. Level 2 - Quoted prices for similar assets and liabilities in active markets or model-based valuation techniques for which all significant inputs are observable in the market (where applicable, these models project future cash flows and discount the future amounts to a present value using market-based observable inputs including interest rate curves, credit spreads, etc.). Our Level 2 non-derivative liabilities primarily include the Core Term Loan Facility and Sinosure Credit Facility. Our Level 2 derivative assets and liabilities primarily include our interest rate caps, collars, and swaps. Level 3 - Inputs that are unobservable (for example cash flow modeling inputs based on assumptions).
Income taxes	11. Income taxes — ​ Net deferred tax assets are recorded to the extent the Company believes these assets will more likely than not be realized. In making such a determination, all available positive and negative evidence is considered, including future reversals of existing taxable temporary differences, projected future taxable income, tax-planning strategies, and results of recent operations. In the event the Company were to determine that it would be able to realize its deferred income tax assets in the future in excess of their net recorded amount, an adjustment would be made to the deferred tax asset valuation allowance, which would reduce the provision for income taxes in the period such determination is made. ​ Uncertain tax positions are recorded in accordance with ASC 740, Income Taxes,
Valuation of equity method investments	12. Valuation of equity method investments —
Use of estimates	13. Use of estimates
Recently adopted / issued accounting standards	14. Recently adopted accounting standards — Financial Instruments – Credit Losses is deemed uncollectible will be written off in a manner consistent with existing standards. In addition, for guarantees in the scope of ASC 326, entities must measure the expected credit losses arising from the contingent aspect under the CECL model in addition to recognizing the liability for the noncontingent aspect of the guarantee under ASC 460, Guarantees Financial Instruments – Credit Losses ​ In August 2018, the FASB issued ASU 2018-14, Defined Benefit Plans ​ In August 2018, the FASB issued ASU 2018-13, Fair Value Measurement year ended December 31, 2020. ​ On May 20, 2020, the SEC issued a final rule that amends the financial statement requirements for acquisitions and dispositions of businesses. Among other changes, the final rule modifies the significance tests and disclosure requirements for (i) acquired or to be acquired businesses, (ii) real estate operations, (iii) pro forma financial information and (iv) equity method investees. Key amendments in the final rule will (i) change the investment test to use the aggregate worldwide market value of common equity of the registrant when a registrant is evaluating businesses for significance ; and (ii) change the income test to use the lower measure of significance based on (1) income from continuing operations before taxes or (2) revenue. The new rule requires the use of absolute values of five years income instead of zeros for loss years. However, the amendments also limit the use of income averaging to situations in which the revenue test is not applicable (i.e., either the registrant or the acquiree did not have material revenue in each of the two most recently completed fiscal years). Because we do have material revenue in the past two years, we can’t use five year averaging. The final rule is applicable for a registrant’s fiscal year beginning after December 31, 2020 and early application is permitted. The Company adopted this final rule to take advantage of the revenue test in evaluating the significance of our joint ventures accounted for using the equity method. ​ 15. Recently issued accounting standards — Reference Rate Reform which provides relief for companies preparing for discontinuation of interest rates such as LIBOR. A contract modification is eligible to apply the optional relief to account for the modifications as a continuation of the existing contracts without additional analysis and consider embedded features to be clearly and closely related to the host contract without reassessment, if all of the following criteria are met: (i) contract references a rate that will be discontinued; (ii) modified terms directly replace (or have potential to replace) this reference rate; and (iii) changes to any other terms that change (or have potential to change) amount and timing of cash flows must be related to replacement of the reference rate. In addition, this guidance provides relief from certain hedge accounting requirements. Hedge accounting may continue uninterrupted when critical terms change due to reference rate reform. For cash flow hedges, entities can (i) disregard potential discontinuation of a referenced interest rate when assessing whether a hedged forecasted interest payment is probable; (ii) continue hedge accounting upon a change in the hedged risk as long as the hedge is still highly effective; (iii) assess effectiveness of the hedge relationship in ways that essentially disregards a potential mismatch in the variable rate indices between the hedging instrument and the hedged item; and (iv) disregard the requirement that individual hedged transactions must share the same risk exposure for hedges of portfolios of forecasted transactions that reference a rate affected by reference rate reform. Relief provided by this ASU is optional and expires December 31, 2022. In January 2021, the FASB issued ASU 2021-01, Reference Rate Reform

CONTINGENCIES (Policy)

CONTINGENCIES (Policy)	12 Months Ended
	Dec. 31, 2020
CONTINGENCIES [Abstract]
Legal costs	INSW’s policy for recording legal costs related to contingencies is to expense such legal costs as incurred.

SUMMARY OF SIGNIFICANT ACCOUN_2

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Tables)	12 Months Ended
	Dec. 31, 2020
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES [Abstract]
Activity for allowance for credit losses	​ ​ ​ ​ ​ (Dollars in thousands) ​ ​ Allowance for Credit Losses - Voyage Receivables Balance at January 1, 2018 ​ $ — Provision for expected credit losses ​ ​ — Balance at December 31, 2018 ​ ​ — Provision for expected credit losses ​ ​ 1,245 Balance at December 31, 2019 ​ ​ 1,245 Provision for expected credit losses ​ ​ 58 Write-offs charged against the allowance ​ ​ (1,119) Recoveries of amounts previously written off ​ ​ (129) Balance at December 31, 2020 ​ $ 55

EARNINGS PER COMMON SHARE (Tabl

EARNINGS PER COMMON SHARE (Tables)	12 Months Ended
	Dec. 31, 2020
EARNINGS PER COMMON SHARE [Abstract]
Components of Calculation of Earnings Per Share	Reconciliations of the numerator of the basic and diluted earnings per share computations are as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (Dollars in thousands) ​ ​ 2020 ​ ​ 2019 ​ ​ 2018 Net loss allocated to: ​ ​ ​ ​ ​ ​ ​ ​ ​ Common Stockholders ​ $ (5,544) ​ $ (830) ​ $ (88,940) Participating securities ​ ​ 13 ​ ​ — ​ ​ — ​ ​ $ (5,531) ​ $ (830) ​ $ (88,940) ​

BUSINESS AND SEGMENT REPORTING

BUSINESS AND SEGMENT REPORTING (Tables)	12 Months Ended
	Dec. 31, 2020
BUSINESS AND SEGMENT REPORTING [Abstract]
Schedule of Segment Reporting Information, by Segment	​ ​ Information about the Company’s reportable segments as of and for each of the years in the three-year period ended December 31, 2020 follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Crude ​ Product ​ ​ ​ ​ ​ ​ (Dollars in thousands) ​ Tankers ​ Carriers ​ Other ​ Totals 2020 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Shipping revenues ​ $ 334,765 ​ $ 86,883 ​ $ — ​ $ 421,648 Time charter equivalent revenues ​ ​ 318,588 ​ ​ 83,417 ​ ​ — ​ ​ 402,005 Depreciation and amortization ​ ​ 57,980 ​ ​ 16,269 ​ ​ 94 ​ ​ 74,343 Loss on disposal of vessels and other property, including impairments ​ ​ 44,330 ​ ​ 55,757 ​ ​ — ​ ​ 100,087 Adjusted income/(loss) from vessel operations ​ ​ 144,451 ​ ​ 24,818 ​ ​ (94) ​ ​ 169,175 Equity in income of affiliated companies ​ ​ 4,119 ​ ​ — ​ ​ — ​ ​ 4,119 Investments in and advances to affiliated companies at December 31, 2020 ​ ​ 134,439 ​ ​ 7,485 ​ ​ — ​ ​ 141,924 Adjusted total assets at December 31, 2020 ​ ​ 1,112,342 ​ ​ 253,990 ​ ​ — ​ ​ 1,366,332 Expenditures for vessels and vessel improvements ​ ​ 27,858 ​ ​ 22,191 ​ ​ — ​ ​ 50,049 Payments for drydocking ​ ​ 20,313 ​ ​ 5,329 ​ ​ — ​ ​ 25,642 2019 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Shipping revenues ​ $ 285,356 ​ $ 80,828 ​ $ — ​ $ 366,184 Time charter equivalent revenues ​ ​ 259,517 ​ ​ 80,402 ​ ​ — ​ ​ 339,919 Depreciation and amortization ​ ​ 59,387 ​ ​ 16,152 ​ ​ 114 ​ ​ 75,653 Loss on disposal of vessels and other property ​ ​ 82 ​ ​ 226 ​ ​ — ​ ​ 308 Adjusted income/(loss) from vessel operations ​ ​ 71,344 ​ ​ 12,319 ​ ​ (114) ​ ​ 83,549 Equity in income/(loss) of affiliated companies ​ ​ 19,383 ​ ​ — ​ ​ (8,170) ​ ​ 11,213 Investments in and advances to affiliated companies at December 31, 2019 ​ ​ 143,095 ​ ​ 10,197 ​ ​ — ​ ​ 153,292 Adjusted total assets at December 31, 2019 ​ ​ 1,284,631 ​ ​ 313,063 ​ ​ — ​ ​ 1,597,694 Expenditures for vessels and vessel improvements ​ ​ 33,384 ​ ​ 3,223 ​ ​ — ​ ​ 36,607 Payments for drydocking ​ ​ 16,997 ​ ​ 2,549 ​ ​ — ​ ​ 19,546 2018 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Shipping revenues ​ $ 202,396 ​ $ 67,965 ​ $ — ​ $ 270,361 Time charter equivalent revenues ​ ​ 175,524 ​ ​ 67,576 ​ ​ — ​ ​ 243,100 Depreciation and amortization ​ ​ 54,431 ​ ​ 17,862 ​ ​ 135 ​ ​ 72,428 Loss/(gain) on disposal of vessels and other property, including impairments ​ ​ 22,992 ​ ​ (3,312) ​ ​ — ​ ​ 19,680 Adjusted income/(loss) from vessel operations ​ ​ 2,194 ​ ​ (12,002) ​ ​ 567 ​ ​ (9,241) Equity in income of affiliated companies ​ ​ 19,582 ​ ​ — ​ ​ 9,850 ​ ​ 29,432 Investments in and advances to affiliated companies at December 31, 2018 ​ ​ 143,789 ​ ​ 12,321 ​ ​ 112,212 ​ ​ 268,322 Adjusted total assets at December 31, 2018 ​ ​ 1,285,433 ​ ​ 328,792 ​ ​ 112,212 ​ ​ 1,726,437 Expenditures for vessels and vessel improvements ​ ​ 146,322 ​ ​ 2,624 ​ ​ — ​ ​ 148,946 Payments for drydocking ​ ​ 4,121 ​ ​ 399 ​ ​ — ​ ​ 4,520
Reconciliation of Revenue from Segments to Consolidated	Reconciliations of time charter equivalent revenues of the segments to shipping revenues as reported in the consolidated statements of operations follow: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (Dollars in thousands) ​ ​ 2020 ​ ​ 2019 ​ ​ 2018 Time charter equivalent revenues ​ $ 402,005 ​ $ 339,919 ​ $ 243,100 Add: Voyage expenses ​ ​ 19,643 ​ ​ 26,265 ​ ​ 27,261 Shipping revenues ​ $ 421,648 ​ $ 366,184 ​ $ 270,361 ​
Reconciliation of Operating Profit (Loss) from Segments to Consolidated	Reconciliations of adjusted income/(loss) from vessel operations of the segments to income/(loss) before income taxes, as reported in the consolidated statements of operations follow: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (Dollars in thousands) ​ ​ 2020 ​ ​ 2019 ​ ​ 2018 Total adjusted income/(loss) from vessel operations of all segments ​ $ 169,175 ​ $ 83,549 ​ $ (9,241) General and administrative expenses ​ ​ (29,047) ​ ​ (26,798) ​ ​ (24,304) Provision for credit losses, net ​ ​ 71 ​ ​ (1,245) ​ ​ — Third-party debt modification fees ​ ​ (232) ​ ​ (30) ​ ​ (1,306) Loss on disposal of vessels and other property, including impairments ​ ​ (100,087) ​ ​ (308) ​ ​ (19,680) Consolidated income/(loss) from vessel operations ​ ​ 39,880 ​ ​ 55,168 ​ ​ (54,531) Equity in income of affiliated companies ​ ​ 4,119 ​ ​ 11,213 ​ ​ 29,432 Other expense ​ ​ (12,817) ​ ​ (943) ​ ​ (3,715) Interest expense ​ ​ (36,712) ​ ​ (66,267) ​ ​ (60,231) Income/(loss) before income taxes ​ $ (5,530) ​ $ (829) ​ $ (89,045) ​
Reconciliation of Assets from Segment to Consolidated	Reconciliations of adjusted total assets of the segments to amounts included in the consolidated balance sheets follow: ​ ​ ​ ​ ​ ​ ​ ​ (Dollars in thousands) ​ December 31, 2020 ​ December 31, 2019 Adjusted total assets of all segments ​ $ 1,366,332 ​ $ 1,597,694 Corporate unrestricted cash and cash equivalents ​ ​ 199,390 ​ ​ 89,671 Restricted cash ​ ​ 16,287 ​ ​ 60,572 Other unallocated amounts ​ ​ 4,530 ​ ​ 5,564 Consolidated total assets ​ $ 1,586,539 ​ $ 1,753,501 ​
Long Lived Assets Deployment by Segment	Certain additional information about the Company’s operations for each of the years in the three year period ended December 31, 2020 follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Crude ​ Product ​ ​ ​ ​ ​ ​ (Dollars in thousands) ​ Tankers ​ Carriers ​ ​ Other ​ Consolidated Total vessels, deferred drydock and other property at December 31, 2020 ​ $ 919,974 ​ $ 224,507 ​ $ 67 ​ $ 1,144,548 Total vessels, deferred drydock and other property at December 31, 2019 ​ ​ 1,051,848 ​ ​ 263,651 ​ ​ 142 ​ ​ 1,315,641 Total vessels, deferred drydock and other property at December 31, 2018 ​ ​ 1,057,994 ​ ​ 289,317 ​ ​ 257 ​ ​ 1,347,568

VESSELS, DEFERRED DRYDOCK AND_2

VESSELS, DEFERRED DRYDOCK AND OTHER PROPERTY (Tables)	12 Months Ended
	Dec. 31, 2020
Property, Plant and Equipment [Line Items]
Schedule of Property	Vessels and other property, excluding vessel held for sale, consist of the following: ​ ​ ​ ​ ​ ​ ​ ​ (Dollars in thousands) ​ December 31, 2020 ​ December 31, 2019 Vessels, at cost ​ $ 1,287,688 ​ $ 1,650,670 Accumulated depreciation ​ ​ (182,148) ​ ​ (361,088) Vessels, net ​ ​ 1,105,540 ​ ​ 1,289,582 Other property, at cost ​ ​ 6,610 ​ ​ 6,714 Accumulated depreciation and amortization ​ ​ (3,936) ​ ​ (3,780) Other property, net ​ ​ 2,674 ​ ​ 2,934 Total Vessels and other property ​ $ 1,108,214 ​ $ 1,292,516 ​
Schedule of Property Plant and Equipment by Segment	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net ​ ​ Average ​ ​ Number of ​ ​ ​ ​ ​ Accumulated ​ Carrying ​ ​ Vessel Age ​ ​ Owned As of December 31, 2020 (Dollars in thousands) ​ Cost ​ Depreciation ​ Value ​ ​ (by dwt) ​ ​ Vessels Crude Tankers ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ VLCC ​ $ 839,542 ​ $ (131,862) ​ $ 707,680 ​ ​ 7.9 ​ ​ 11 Suezmax ​ ​ 117,338 ​ ​ (14,099) ​ ​ 103,239 ​ ​ 3.4 ​ ​ 2 Aframax (1) ​ ​ 32,395 ​ ​ (1,378) ​ ​ 31,017 ​ ​ 7.5 ​ ​ 1 Panamax ​ ​ 57,992 ​ ​ (8,111) ​ ​ 49,881 ​ ​ 18.2 ​ ​ 7 Total Crude Tankers ​ ​ 1,047,267 ​ ​ (155,450) ​ ​ 891,817 (2) ​ 8.8 ​ ​ 21 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Product Carriers ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ LR2 ​ ​ 73,710 ​ ​ (17,419) ​ ​ 56,291 ​ ​ 6.4 ​ ​ 1 LR1 ​ ​ 96,838 ​ ​ (9,279) ​ ​ 87,559 ​ ​ 11.9 ​ ​ 5 MR ​ ​ 69,873 ​ ​ — ​ ​ 69,873 ​ ​ 10.0 ​ ​ 4 Total Product Carriers ​ ​ 240,421 ​ ​ (26,698) ​ ​ 213,723 (3) ​ 10.5 ​ ​ 10 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fleet Total ​ $ 1,287,688 ​ $ (182,148) ​ $ 1,105,540 ​ ​ 9.0 ​ ​ 31 (1) Net carrying value includes assets capitalized on two bareboat chartered-in Aframaxes. (2) Includes 10 VLCCs and one Panamax with an aggregate carrying value of $695.3 million, which the Company believes exceeds their aggregate market values (estimated by taking an average of two third party vessel appraisals) of approximately $584.0 million by $111.3 million. (3) Includes one LR2 and three LR1s with an aggregate carrying value of $106.3 million, which the Company believes exceeds their aggregate market values (estimated by taking an average of two third party vessel appraisals) of approximately $75.6 million by $30.7 million. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net ​ ​ Average ​ ​ Number of ​ ​ ​ ​ ​ Accumulated ​ Carrying ​ ​ Vessel Age ​ ​ Owned As of December 31, 2019 (Dollars in thousands) ​ Cost ​ Depreciation ​ Value ​ ​ (by dwt) ​ ​ Vessels Crude Tankers ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ VLCC ​ $ 1,028,760 ​ $ (236,217) ​ $ 792,543 ​ ​ 8.6 ​ ​ 13 Suezmax ​ ​ 117,338 ​ ​ (10,007) ​ ​ 107,331 ​ ​ 2.4 ​ ​ 2 Aframax ​ ​ 96,038 ​ ​ (19,659) ​ ​ 76,379 ​ ​ 14.1 ​ ​ 3 Panamax ​ ​ 59,181 ​ ​ (5,223) ​ ​ 53,958 ​ ​ 17.2 ​ ​ 7 Total Crude Tankers ​ ​ 1,301,317 ​ ​ (271,106) ​ ​ 1,030,211 ​ ​ 9.4 ​ ​ 25 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Product Carriers ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ LR2 ​ ​ 73,681 ​ ​ (14,714) ​ ​ 58,967 ​ ​ 5.4 ​ ​ 1 LR1 ​ ​ 108,251 ​ ​ (22,420) ​ ​ 85,831 ​ ​ 11.0 ​ ​ 4 MR ​ ​ 167,421 ​ ​ (52,848) ​ ​ 114,573 ​ ​ 9.0 ​ ​ 4 Total Product Carriers ​ ​ 349,353 ​ ​ (89,982) ​ ​ 259,371 ​ ​ 9.3 ​ ​ 9 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fleet Total ​ $ 1,650,670 ​ $ (361,088) ​ $ 1,289,582 ​ ​ 9.4 ​ ​ 34
Vessel/Fleet [Member]
Property, Plant and Equipment [Line Items]
Schedule of Property Plant and Equipment by Segment	​ ​ Vessel activity for the three years ended December 31, 2020 is summarized as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (Dollars in thousands) ​ Vessel Cost ​ Accumulated Depreciation ​ Net Book Value Balance at January 1, 2018 ​ $ 1,404,360 ​ $ (302,087) ​ $ 1,102,273 Purchases and vessel additions ​ ​ 459,608 ​ ​ — ​ ​ ​ Disposals ​ ​ (176,300) ​ ​ 16,097 ​ ​ ​ Depreciation ​ ​ — ​ ​ (56,711) ​ ​ ​ Impairment ​ ​ (58,021) ​ ​ 40,816 ​ ​ ​ Balance at December 31, 2018 ​ ​ 1,629,647 ​ ​ (301,885) ​ ​ 1,327,762 Purchases and vessel additions ​ ​ 38,138 ​ ​ — ​ ​ ​ Disposals ​ ​ (17,115) ​ ​ 1,105 ​ ​ ​ Depreciation ​ ​ — ​ ​ (60,308) ​ ​ ​ Balance at December 31, 2019 ​ ​ 1,650,670 ​ ​ (361,088) ​ ​ 1,289,582 Purchases and vessel additions ​ ​ 48,436 ​ ​ — ​ ​ ​ Disposals ​ ​ (70,353) ​ ​ 2,763 ​ ​ ​ Depreciation ​ ​ — ​ ​ (61,866) ​ ​ ​ Impairment ​ ​ (341,065) ​ ​ 238,043 ​ ​ ​ Balance at December 31, 2020 ​ $ 1,287,688 ​ $ (182,148) ​ $ 1,105,540
Drydock [Member]
Property, Plant and Equipment [Line Items]
Schedule of Property	Drydocking activity for the three years ended December 31, 2020 is summarized as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (Dollars in thousands) ​ 2020 ​ 2019 ​ 2018 Balance at January 1 ​ $ 23,125 ​ $ 16,773 ​ $ 30,528 Additions ​ ​ 27,835 ​ ​ 21,086 ​ ​ 5,616 Sub-total ​ ​ 50,960 ​ ​ 37,859 ​ ​ 36,144 Drydock amortization ​ ​ (11,780) ​ ​ (14,685) ​ ​ (15,084) Amount charged to loss on disposal of vessels ​ ​ (2,846) ​ ​ (49) ​ ​ (4,287) Balance at December 31 ​ $ 36,334 ​ $ 23,125 ​ $ 16,773

EQUITY METHOD INVESTMENTS (Tabl

EQUITY METHOD INVESTMENTS (Tables)	12 Months Ended
	Dec. 31, 2020
EQUITY METHOD INVESTMENTS [Abstract]
Results of Operations of Equity Method Investments	​ Financial information for the equity method investees that were significant for the three years ended December 31, 2020, including the results of the LNG Joint Venture prior to the sale on October 7, 2019, adjusted for basis and accounting policy differences, is as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (Dollars in thousands) ​ 2020 ​ 2019 ​ 2018 Shipping revenues ​ $ 105,053 ​ $ 193,446 ​ $ 209,571 Ship operating expenses ​ ​ (58,858) ​ ​ (103,499) ​ ​ (112,541) Income from vessel operations ​ ​ 46,195 ​ ​ 89,947 ​ ​ 97,030 Other income ​ ​ 22 ​ ​ 1,459 ​ ​ 1,494 Interest expense ​ ​ (6,571) ​ ​ (32,752) ​ ​ (40,676) Income tax provision ​ ​ (36,404) ​ ​ (3,399) ​ ​ (3,433) Net income ​ $ 3,242 ​ $ 55,255 ​ $ 54,415 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Percentage of ownership in equity investees ​ ​ 50.0% ​ ​ 49.9% - 50.0% ​ ​ 49.9% - 50.0% Equity in income of affiliated companies, before consolidating and reconciling adjustments ​ $ 1,621 ​ $ 27,606 ​ $ 27,187 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Gain on sale of investments in affiliated companies ​ ​ — ​ ​ 3,033 ​ ​ — Release other comprehensive loss upon sale of investment in affiliated companies ​ ​ — ​ ​ (21,615) ​ ​ — Amortization of deferred gain on 2009 sale of TI Africa to FSO Joint Venture ​ ​ 2,385 ​ ​ 2,395 ​ ​ 2,395 Amortization of interest capitalized during construction of LNG vessels ​ ​ — ​ ​ (320) ​ ​ (419) Other ​ ​ 113 ​ ​ 114 ​ ​ 269 Equity in income of affiliated companies ​ $ 4,119 ​ $ 11,213 ​ $ 29,432 ​
Equity Method Investments Summarized Balance Sheet Information	​ ​ ​ ​ ​ ​ ​ ​ (Dollars in thousands) ​ December 31, 2020 ​ December 31, 2019 Current assets ​ $ 20,154 ​ $ 20,808 Vessels, net ​ ​ 490,093 ​ ​ 523,802 Total assets ​ $ 510,247 ​ $ 544,610 ​ ​ ​ ​ ​ ​ ​ Current liabilities ​ $ 59,567 ​ $ 53,774 Long-term debt and other non-current liabilities ​ ​ 111,263 ​ ​ 143,673 Equity ​ ​ 339,417 ​ ​ 347,163 Total liabilities and equity ​ $ 510,247 ​ $ 544,610 ​ ​ ​ ​ ​ ​ ​ Percentage of ownership in equity investees ​ ​ 50.0% ​ ​ 50.0% INSW share of affiliate's equity, before consolidating and reconciling adjustments ​ $ 169,708 ​ $ 173,581 ​ ​ ​ ​ ​ ​ ​ 2016 impairment of equity method investments in FSO Joint Venture ​ ​ (30,475) ​ ​ (30,475) Advances from shareholders of FSO Joint Venture (1) ​ ​ 16,665 ​ ​ 23,216 Unamortized deferred gain on 2009 sale of TI Africa to FSO Joint Venture, net ​ ​ (27,156) ​ ​ (29,503) INSW guarantee for FSO Term Loan ​ ​ 44 ​ ​ 264 Other (2) ​ ​ 13,138 ​ ​ 16,209 Investments in and advances to affiliated companies ​ $ 141,924 ​ $ 153,292 (1) Such advances are unsecured, interest free and not repayable within one year. (2) Primarily relates to working capital deposits that the Company maintains with the commercial pools in which it participates. ​

VARIABLE INTEREST ENTITIES (V_2

VARIABLE INTEREST ENTITIES (VIEs)) (Tables)	12 Months Ended
	Dec. 31, 2020
VARIABLE INTEREST ENTITIES (VIEs) [Abstract]
Schedule of Variable Interest Entities	The following table presents the carrying amounts of assets and liabilities in the consolidated balance sheets related to the VIEs described above as of December 31, 2020 and 2019: ​ ​ ​ ​ ​ ​ ​ ​ (Dollars in thousands) ​ 2020 ​ 2019 Investments in Affiliated Companies ​ $ 132,902 ​ $ 140,915 ​
Schedule of Variable Interest Entities Liability in Condensed Consolidated Balance Sheet to Maximum Exposure to Loss	In accordance with accounting guidance, the Company evaluated its maximum exposure to loss related to these VIEs by assuming a complete loss of the Company’s investment in these VIEs and the Company’s potential obligations under its guarantee of the FSO Term Loan and associated interest rate swap. The table below compares the Company’s liability in the consolidated balance sheet to the maximum exposure to loss at December 31, 2020: ​ ​ ​ ​ ​ ​ ​ ​ (Dollars in thousands) ​ ​ Consolidated Balance Sheet ​ ​ Maximum Exposure to Loss Other Liabilities ​ $ 44 ​ $ 179,291

DEBT (Tables)

DEBT (Tables)	12 Months Ended
	Dec. 31, 2020
DEBT [Abstract]
Schedule of Long-term Debt Instruments	​ ​ ​ ​ ​ ​ ​ ​ (Dollars in thousands) ​ December 31, 2020 ​ December 31, 2019 Core Term Loan Facility, due 2025, net of unamortized deferred finance costs of $4,145 ​ $ 267,427 ​ $ — Sinosure Credit Facility, due 2027-2028, net of unamortized deferred finance costs of $1,884 and $2,262 ​ ​ 244,243 ​ ​ 267,443 8.5% Senior Notes, due 2023, net of unamortized deferred finance costs of $855 and $1,142 ​ ​ 24,145 ​ ​ 23,858 2017 Term Loan Facility, due 2022, net of unamortized discount and deferred finance costs of $11,211 ​ ​ — ​ ​ 320,309 ABN Term Loan Facility, due 2023, net of unamortized deferred finance costs of $610 ​ ​ — ​ ​ 22,638 10.75% Subordinated Notes, due 2023, net of unamortized deferred finance costs of $1,084 ​ ​ — ​ ​ 26,847 ​ ​ ​ 535,815 ​ ​ 661,095 Less current portion ​ ​ (61,483) ​ ​ (70,350) Long-term portion ​ $ 474,332 ​ $ 590,745
Contractual Obligation, Fiscal Year Maturity Schedule	As of December 31, 2020, the aggregate annual principal payments required to be made on the Company’s debt facilities are as follows: ​ ​ ​ ​ ​ (Dollars in thousands) ​ Amount 2021 ​ $ 61,483 2022 ​ ​ 61,483 2023 ​ ​ 86,484 2024 ​ ​ 61,483 2025 ​ ​ 143,532 Thereafter ​ ​ 128,233 Aggregate principal payments required ​ $ 542,698
Schedule of Interest Paid	The following table summarizes interest expense, including amortization of issuance and deferred financing costs (for additional information related to deferred financing costs see Note 2, “Significant Accounting Policies”), commitment, administrative and other fees, recognized during the years ended December 31, 2020, 2019 and 2018 with respect to the Company’s debt facilities: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (Dollars in thousands) ​ 2020 ​ 2019 ​ 2018 Core Term Loan Facility, due 2025 ​ $ 13,542 ​ $ — ​ $ — Transition Term Loan Facility ​ ​ 1,518 ​ ​ — ​ ​ — Core Revolving Facility ​ ​ 660 ​ ​ — ​ ​ — 2017 Term Loan Facility ​ ​ 3,628 ​ ​ 41,483 ​ ​ 45,601 2017 Revolver Facility ​ ​ 63 ​ ​ 848 ​ ​ 475 ABN Term Loan Facility ​ ​ 107 ​ ​ 1,716 ​ ​ 1,024 Sinosure Credit Facility, due 2027 - 2028 ​ ​ 13,684 ​ ​ 14,903 ​ ​ 8,350 8.5% Senior Notes, due 2023 ​ ​ 2,417 ​ ​ 2,390 ​ ​ 1,396 10.75% Subordinated Notes ​ ​ 276 ​ ​ 3,642 ​ ​ 2,032 Total debt related interest expense ​ $ 35,895 ​ $ 64,982 ​ $ 58,878 ​ The following table summarizes interest paid, excluding deferred financing fees paid, during the years ended December 31, 2020, 2019 and 2018 with respect to the Company’s debt facilities: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (Dollars in thousands) ​ 2020 ​ 2019 ​ 2018 Core Term Loan Facility, due 2025 ​ $ 12,024 ​ $ — ​ $ — Transition Term Loan Facility ​ ​ 1,183 ​ ​ — ​ ​ — Core Revolving Facility ​ ​ 471 ​ ​ — ​ ​ — 2017 Term Loan Facility ​ ​ 2,011 ​ ​ 36,236 ​ ​ 42,825 2017 Revolver Facility ​ ​ 53 ​ ​ 710 ​ ​ 442 ABN Term Loan Facility ​ ​ 156 ​ ​ 1,504 ​ ​ 795 Sinosure Credit Facility, due 2027 - 2028 ​ ​ 12,199 ​ ​ 14,200 ​ ​ 7,225 8.5% Senior Notes, due 2023 ​ ​ 2,130 ​ ​ 2,130 ​ ​ 1,250 10.75% Subordinated Notes ​ ​ 359 ​ ​ 3,021 ​ ​ 1,591 Total debt related interest expense paid ​ $ 30,586 ​ $ 57,801 ​ $ 54,128 ​

FAIR VALUE OF FINANCIAL INSTR_2

FAIR VALUE OF FINANCIAL INSTRUMENTS, DERIVATIVES AND FAIR VALUE DISCLOSURES (Tables)	12 Months Ended
	Dec. 31, 2020
FAIR VALUE OF FINANCIAL INSTRUMENTS, DERIVATIVES AND FAIR VALUE DISCLOSURES [Abstract]
Fair Value, by Balance Sheet Grouping	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (Dollars in thousands) ​ Fair Value ​ Level 1 ​ Level 2 December 31, 2020: ​ ​ ​ ​ ​ ​ ​ ​ ​ Cash and cash equivalents (1) ​ $ 215,677 ​ $ 215,677 ​ $ — Core Term Loan Facility ​ ​ (271,571) ​ ​ — ​ ​ (271,571) Sinosure Credit Facility ​ ​ (246,127) ​ ​ — ​ ​ (246,127) 8.5% Senior Notes ​ ​ (25,697) ​ ​ (25,697) ​ ​ — ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2019: ​ ​ ​ ​ ​ ​ ​ ​ ​ Cash and cash equivalents (1) ​ $ 150,243 ​ $ 150,243 ​ $ — 2017 Term Loan Facility ​ ​ (333,177) ​ ​ — ​ ​ (333,177) ABN Term Loan Facility ​ ​ (23,248) ​ ​ — ​ ​ (23,248) Sinosure Credit Facility ​ ​ (269,705) ​ ​ — ​ ​ (269,705) 8.5% Senior Notes ​ ​ (26,120) ​ ​ (26,120) ​ ​ — 10.75% Subordinated Notes ​ ​ (32,649) ​ ​ — ​ ​ (32,649) (1) Includes non-current restricted cash of $16.3 million and $60.6 million at December 31, 2020 and 2019, respectively.
Schedule of Derivative Instruments in Statement of Financial Position, Fair Value	Derivatives are recorded on a net basis by counterparty when a legal right of offset exists. The Company had the following amounts recorded on a gross basis by transaction in the accompanying consolidated balance sheets related to the Company’s use of derivatives as of ​ Fair Values of Derivative Instruments: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (Dollars in thousands) ​ Long-term derivative ​ Current portion of derivative liability ​ Long-term derivative ​ Accounts payable, accrued expenses and other current liabilities ​ Other December 31, 2020: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Derivatives designated as cash flow hedges: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Interest rate swaps ​ $ 2,129 ​ $ (4,121) ​ $ (6,155) ​ $ — ​ $ — ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Other-than-insignificant financing element of derivatives: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Interest rate swaps (1) ​ ​ — ​ ​ — ​ ​ — ​ ​ (2,979) ​ ​ (14,051) Total ​ $ 2,129 ​ $ (4,121) ​ $ (6,155) ​ $ (2,979) ​ $ (14,051) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31,2019: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Derivatives designated as cash flow hedges: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Interest rate swaps ​ $ — ​ $ (2,384) ​ $ (5,968) ​ $ — ​ $ — ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Derivatives not designated as cash flow hedges: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Interest rate collar ​ ​ — ​ ​ (1,230) ​ ​ (577) ​ ​ — ​ ​ — Total ​ $ — ​ $ (3,614) ​ $ (6,545) ​ $ — ​ $ — (1) Represents the financing element of the hybrid instrument discussed above, which is recorded at amortized cost. ​
Schedule of Cash Flow Hedges Included in Accumulated Other Comprehensive Loss	The effect of cash flow hedging relationships recognized in other comprehensive loss excluding amounts reclassified from accumulated other comprehensive loss, including hedges of equity method investees, for the three years ended December 31, 2020 follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (Dollars in thousands) ​ 2020 ​ 2019 ​ 2018 Derivatives designated as hedging instruments: ​ ​ ​ ​ ​ ​ ​ Interest rate swaps ​ $ (20,123) ​ $ (15,221) ​ $ (1,948) Interest rate cap/collar ​ ​ — ​ ​ (3,905) ​ ​ 261 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Other-than-insignificant financing element of derivatives: ​ ​ ​ ​ ​ ​ ​ Interest rate swaps ​ ​ (1,380) ​ ​ — ​ ​ — Total other comprehensive loss ​ $ (21,503) ​ $ (19,126) ​ $ (1,687) ​ ​ The effect of cash flow hedging relationships on the consolidated statements of operations is presented excluding hedges of equity method investees. The effect of the Company’s cash flow hedging relationships on the consolidated statement of operations for the three years ended December 31, 2020 is shown below: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (Dollars in thousands) ​ 2020 ​ 2019 ​ 2018 Derivatives designated as hedging instruments: ​ ​ ​ ​ ​ ​ ​ Interest rate swaps ​ $ 4,571 ​ $ 1,467 ​ $ 471 Interest rate cap/collar ​ ​ — ​ ​ 99 ​ ​ 21 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Derivatives not designated as hedging instruments: ​ ​ ​ ​ ​ ​ ​ Interest rate collar ​ ​ 1,352 ​ ​ (65) ​ ​ — ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Other-than-insignificant financing element of derivatives: ​ ​ ​ ​ ​ ​ ​ Interest rate swaps ​ ​ 3,376 ​ ​ — ​ ​ — Total interest expense ​ $ 9,299 ​ $ 1,501 ​ $ 492 ​
Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis	​ ​ ​ ​ ​ ​ ​ ​ ​ (Dollars in thousands) ​ ​ Fair Value ​ ​ Level 2 (1) ​ Assets/(Liabilities) at December 31, 2020: ​ ​ ​ ​ ​ ​ ​ Derivative Assets (interest rate swaps) ​ $ 2,129 ​ $ 2,129 ​ Derivative Liabilities (interest rate swaps) ​ ​ (10,276) ​ ​ (10,276) ​ ​ ​ ​ ​ ​ ​ ​ ​ Assets/(Liabilities) at December 31, 2019: ​ ​ ​ ​ ​ ​ ​ Derivative Assets (interest rate swaps and collar) ​ $ — ​ $ — ​ Derivative Liabilities (interest rate swaps and collar) ​ ​ (10,159) ​ ​ (10,159) ​ (1) For the interest rate cap, collar and swaps, fair values are derived using valuation models that utilize the income valuation approach. These valuation models take into account contract terms such as maturity, as well as other inputs such as interest rate yield curves and creditworthiness of the counterparty and the Company.
Schedule of Fair Value, Assets and Liabilities Measured on Nonrecurring Basis	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Impairment (Dollars in thousands) ​ Fair Value ​ Level 2 ​ Charges Assets: ​ ​ ​ ​ ​ ​ ​ ​ ​ Crude Tankers - Vessels held for use (1)(2) ​ $ 134,035 ​ $ 134,035 ​ $ (47,265) Product Carriers - Vessels held for use (1)(2) ​ $ 113,250 ​ $ 113,250 ​ $ (55,757) (1) Pre-tax impairment charges of $5.5 million related to one VLCC tanker, $11.7 million related to two VLCC tankers, and $30.1 million related to one VLCC tanker and one Aframax in the Crude Tankers segment were recorded during the three-month periods ended June 30, 2020, September 30, 2020, and December 31, 2020, respectively . Pre-tax impairment charges of $55.7 million related to two LR1s and four MRs in the Product Carriers segment were recorded during the three-month period ended December 31, 2020. (2) The fair value measurement of $30.4 million that was used to determine the impairment for one VLCC at June 30, 2020, the fair value measurement of $50.5 million that was used to determine the impairment for two VLCCs at September 30, 2020, and the fair value measurement of $53.1 millon that was used to determine the impairment for one VLCC and one Aframax, and $113.3 million that was used to determine the impairment of two LR1s and four MRs at December 31, 2020, were based upon a market approach, which considered the expected sales price of the vessel obtained from vessel appraisals and executed memoranda of agreements for the sale of each of the vessels as discussed in Note 5, “Vessels.” As sales of vessels occur somewhat infrequently, the expected sales price is considered to be Level 2.

ACCOUNTS PAYABLE, ACCRUED EXP_2

ACCOUNTS PAYABLE, ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES (Tables)	12 Months Ended
	Dec. 31, 2020
ACCOUNTS PAYABLE, ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES [Abstract]
Schedule of Accounts Payable, Accrued Expenses and Other Current Liabilities	​ ​ ​ ​ ​ ​ ​ ​ (Dollars in thousands) ​ December 31, 2020 ​ December 31, 2019 Accounts payable ​ $ 2,609 ​ $ 4,988 Payroll and benefits ​ ​ 6,293 ​ ​ 5,585 Interest ​ ​ 370 ​ ​ 594 Other-than-insignificant financing element of derivatives ​ ​ 2,979 ​ ​ — Due to owners on chartered in vessels ​ ​ 787 ​ ​ 1,108 Accrued drydock, repairs and vessel betterment costs ​ ​ 6,247 ​ ​ 3,150 Bunkers and lubricants ​ ​ 656 ​ ​ 538 Charter revenues received in advance ​ ​ 3,060 ​ ​ 272 Insurance ​ ​ 493 ​ ​ 539 Accrued vessel expenses ​ ​ 8,779 ​ ​ 8,003 Accrued general and administrative expenses ​ ​ 940 ​ ​ 1,052 Other ​ ​ 1,212 ​ ​ 1,725 Total accounts payable, accrued expense and other current liabilities ​ $ 34,425 ​ $ 27,554

TAXES (Tables)

TAXES (Tables)	12 Months Ended
	Dec. 31, 2020
TAXES [Abstract]
Components of Income Tax (Provisions) and Benefits	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (Dollars in thousands) ​ ​ 2020 ​ ​ 2019 ​ ​ 2018 ​ Current ​ $ (1) ​ $ (1) ​ $ 105 ​ Deferred ​ ​ — ​ ​ — ​ ​ — ​ Income tax (provision)/benefit ​ $ (1) ​ $ (1) ​ $ 105 ​
Schedule of Effective Income Tax Rate Reconciliation [Table Text Block]	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2020 ​ ​ 2019 ​ ​ 2018 ​ Change in valuation allowance ​ ​ 0.66 % ​ 0.66 % ​ (0.66) % Income subject to tax in other jurisdictions ​ ​ (0.65) % ​ (0.83) % ​ 0.54 % Effective income tax rate ​ ​ 0.01 % ​ (0.17) % ​ (0.12) %
Components of Deferred Tax Liabilities and Assets	The significant components of the Company’s deferred tax liabilities and assets follow: ​ ​ ​ ​ ​ ​ ​ ​ (Dollars in thousands) ​ December 31, 2020 ​ December 31, 2019 Deferred tax assets: ​ ​ ​ ​ ​ ​ Net operating loss carryforwards ​ $ 2,173 ​ $ 1,836 Excess of tax over book basis of depreciable assets ​ ​ 612 ​ ​ 548 Pensions ​ ​ 1,950 ​ ​ 1,797 Total deferred tax assets ​ ​ 4,735 ​ ​ 4,181 Less: Valuation allowance ​ ​ (4,735) ​ ​ (4,181) Deferred tax assets, net ​ ​ — ​ ​ — Net noncurrent deferred tax assets/(liabilities) ​ $ — ​ $ — ​

CAPITAL STOCK AND STOCK COMPE_2

CAPITAL STOCK AND STOCK COMPENSATION (Tables)	12 Months Ended
	Dec. 31, 2020
CAPITAL STOCK AND STOCK COMPENSATION [Abstract]
Schedule of Share-based Compensation, Restricted Stock Units Award Activity	​ ​ ​ ​ ​ ​ Common Stock Nonvested Shares Outstanding at December 31, 2017 ​ 174,177 Granted (2) ​ 173,573 Forfeitures (3) ​ (19,995) Vested ($18.62 - $24.05 per share) (1) ​ (97,554) Nonvested Shares Outstanding at December 31, 2018 ​ 230,201 Granted (2) ​ 270,096 Forfeitures (3) ​ (20,570) Vested ($17.46- $29.61 per share) (1) ​ (126,863) Nonvested Shares Outstanding at December 31, 2019 ​ 352,864 Granted (2) ​ 182,142 Forfeitures (3) ​ — Vested ($17.21- $27.66 per share) (1) ​ (229,123) Nonvested Shares Outstanding at December 31, 2020 ​ 305,883 (1) Includes 71,513 (2020), 21,529 (2019) and 21,752 (2018) shares of common stock sold back to the Company by employees to cover withholding taxes in the year of vesting or during the first quarter of the subsequent year. (2) Includes 8,309 , 8,198 and 3,120 incremental performance restricted stock units earned as a result of above target achievement of market condition at December 31, 2020, 2019 and 2018, respectively. (3) Represents restricted stock units forfeited because performance targets were not achieved as of the measurement date. ​
Schedule of Share-based Compensation, Stock Options, Activity	​ Activity with respect to stock options under INSW compensation plans is summarized as follows: ​ ​ ​ ​ ​ ​ Common Stock Options Outstanding at December 31, 2017 ​ 275,830 Granted ​ 124,955 Exercised ​ — Options Outstanding at December 31, 2018 ​ 400,785 Granted ​ 137,847 Exercised ​ — Options Outstanding at December 31, 2019 ​ 538,632 Granted ​ 131,992 Exercised ​ — Options Outstanding at December 31, 2020 ​ 670,624 Options Exercisable at December 31, 2020 ​ 405,082 ​

ACCUMULATED OTHER COMPREHENSI_2

ACCUMULATED OTHER COMPREHENSIVE LOSS (Tables)	12 Months Ended
	Dec. 31, 2020
ACCUMULATED OTHER COMPREHENSIVE LOSS [Abstract]
Components of Accumulated Other Comprehensive Loss	The components of accumulated other comprehensive loss, net of related taxes, in the consolidated balance sheets follow: ​ ​ ​ ​ ​ ​ ​ (Dollars in thousands) ​ December 31, 2020 ​ December 31, 2019 Unrealized losses on derivative instruments ​ $ (24,098) ​ $ (11,732) Items not yet recognized as a component of net periodic benefit cost (pension plans) ​ ​ (8,515) ​ ​ (8,838) ​ ​ $ (32,613) ​ $ (20,570) ​ The following tables present the changes in the balances of each component of accumulated other comprehensive loss, net of related taxes, for the three years ended December 31, 2020. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (Dollars in thousands) ​ Unrealized losses on cash flow hedges ​ Items not yet recognized as a component of net periodic benefit cost (pension plans) ​ Total Balance at December 31, 2017 ​ $ (28,989) ​ $ (11,418) ​ $ (40,407) Current period change, excluding amounts reclassified from accumulated other comprehensive loss ​ ​ (1,687) ​ ​ 1,107 ​ ​ (580) Amounts reclassified from accumulated other comprehensive loss ​ ​ 9,156 ​ ​ 1,902 ​ ​ 11,058 Balance at December 31, 2018 ​ ​ (21,520) ​ ​ (8,409) ​ ​ (29,929) Current period change, excluding amounts reclassified from accumulated other comprehensive loss ​ ​ (19,126) ​ ​ (818) ​ ​ (19,944) Amounts reclassified from accumulated other comprehensive loss ​ ​ 28,914 ​ ​ 389 ​ ​ 29,303 Balance at December 31, 2019 ​ ​ (11,732) ​ $ (8,838) ​ ​ (20,570) Current period change, excluding amounts reclassified from accumulated other comprehensive loss ​ ​ (21,503) ​ ​ (61) ​ ​ (21,564) Amounts reclassified from accumulated other comprehensive loss ​ ​ 9,137 ​ ​ 384 ​ ​ 9,521 Balance at December 31, 2020 ​ $ (24,098) ​ $ (8,515) ​ $ (32,613) ​
Reclassification Out of Accumulated Other Comprehensive Income (Loss)	The following table presents information with respect to amounts reclassified out of accumulated other comprehensive loss for the three years ended December 31, 2020. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (Dollars in thousands) ​ ​ 2020 ​ ​ 2019 ​ ​ 2018 ​ Statement of Operations Reclassifications of losses on cash flow hedges: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Interest rate swaps entered into by the Company's equity method ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Equity in income of joint venture investees ​ $ 1,109 ​ $ 26,490 ​ $ 8,664 ​ affiliated companies Interest rate swaps entered into by the Company's subsidiaries ​ ​ 4,571 ​ ​ 1,467 ​ ​ 471 ​ Interest expense Interest rate cap/collar entered into by the Company's subsidiaries ​ ​ — ​ ​ 99 ​ ​ 21 ​ Interest expense ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Reclassifications of losses on derivatives subsequent to ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ discontinuation of hedge accounting ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Interest rate collar entered into by the Company's subsidiaries ​ ​ 81 ​ ​ 858 ​ ​ — ​ Interest expense ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Reclassifications of losses on other-than-insignificant financing ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ element of derivatives: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Interest rate swaps entered into by the Company's subsidiaries ​ ​ 3,376 ​ ​ — ​ ​ — ​ Interest expense ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Items not yet recognized as a component of net periodic benefit cost ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (pension plans): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net periodic benefit costs associated with pension and ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ postretirement benefit plans ​ ​ 384 ​ ​ 389 ​ ​ 1,902 ​ Other expense Total before and net of tax ​ $ 9,521 ​ $ 29,303 ​ $ 11,058 ​ ​

REVENUE (Tables)

REVENUE (Tables)	12 Months Ended
	Dec. 31, 2020
REVENUE [Abstract]
Schedule of Disaggregated Revenue	​ ​ The following table presents the Company’s revenues from leases accounted for under ASC 842 and revenues from services accounted for under ASC 606 for the years ended December 31, 2020, 2019 and 2018: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Crude ​ Product ​ ​ ​ ​ ​ ​ (Dollars in thousands) ​ Tankers ​ Carriers ​ Other ​ Totals 2020 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Revenues from leases ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Pool revenues ​ $ 198,316 ​ $ 74,664 ​ $ — ​ $ 272,980 Time and bareboat charter revenues ​ ​ 87,783 ​ ​ 936 ​ ​ — ​ ​ 88,719 Voyage charter revenues from non-variable lease payments (1) ​ ​ 19,016 ​ ​ 10,456 ​ ​ — ​ ​ 29,472 Voyage charter revenues from variable lease payments ​ ​ 1,180 ​ ​ 827 ​ ​ — ​ ​ 2,007 Revenues from services ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Voyage charter revenues ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Service revenue from voyage charters ​ ​ 472 ​ ​ — ​ ​ — ​ ​ 472 Lightering services ​ ​ 27,998 ​ ​ — ​ ​ — ​ ​ 27,998 Total shipping revenues ​ $ 334,765 ​ $ 86,883 ​ $ — ​ $ 421,648 2019 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Revenues from leases ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Pool revenues ​ $ 173,751 ​ $ 80,304 ​ $ — ​ $ 254,055 Time and bareboat charter revenues ​ ​ 27,535 ​ ​ 90 ​ ​ — ​ ​ 27,625 Voyage charter revenues from non-variable lease payments (1) ​ ​ 29,786 ​ ​ 434 ​ ​ — ​ ​ 30,220 Voyage charter revenues from variable lease payments ​ ​ 2,574 ​ ​ — ​ ​ — ​ ​ 2,574 Revenues from services ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Voyage charter revenues ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Lightering services ​ ​ 51,710 ​ ​ — ​ ​ — ​ ​ 51,710 Total shipping revenues ​ $ 285,356 ​ $ 80,828 ​ $ — ​ $ 366,184 2018 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Revenues from leases ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Pool revenues ​ $ 111,214 ​ $ 65,992 ​ $ — ​ $ 177,206 Time and bareboat charter revenues ​ ​ 24,088 ​ ​ 1,873 ​ ​ — ​ ​ 25,961 Voyage charter revenues from non-variable lease payments (1) ​ ​ 20,682 ​ ​ 100 ​ ​ — ​ ​ 20,782 Voyage charter revenues from variable lease payments ​ ​ 1,346 ​ ​ — ​ ​ — ​ ​ 1,346 Revenues from services ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Voyage charter revenues ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Lightering services ​ ​ 45,066 ​ ​ — ​ ​ — ​ ​ 45,066 Total shipping revenues ​ $ 202,396 ​ $ 67,965 ​ $ — ​ $ 270,361 (1) Includes $4.4 million, $0.3 million and $2.3 million of loss of hire insurance proceeds received during the years ended December 31, 2020, 2019 and 2018, respectively. All such proceeds were associated with vessels in our Crude Tankers segment except for the 2019 proceeds which was associated with a vessel in the Product Carriers segment. ​
Schedule of Contract Related Receivables, Assets and Liabilities with Customers	The following table provides information about receivables, contract assets and contract liabilities from contracts with customers, and significant changes in contract assets and liabilities balances, associated with revenue from services accounted for under ASC 606. Balances related to revenues from leases accounted for under ASC 842 are excluded from the table below. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (Dollars in thousands) ​ Voyage receivables - Billed receivables ​ Contract assets (Unbilled voyage receivables) ​ Contract liabilities (Deferred revenues and off hires) Opening balance as of January 1, 2020 ​ $ 2,727 ​ $ — ​ $ — Closing balance as of December 31, 2020 ​ ​ 2,148 ​ ​ 166 ​ ​ —

LEASES (Tables)

LEASES (Tables)	12 Months Ended
	Dec. 31, 2020
Lease [Abstract]
Schedule of lease cost	​ ​ ​ ​ ​ ​ ​ ​ (Dollars in thousands) ​ ​ 2020 ​ ​ 2019 Operating lease cost ​ ​ ​ ​ ​ ​ Vessel assets ​ ​ ​ ​ ​ ​ Charter hire expenses ​ $ 11,666 ​ $ 15,089 ​ ​ ​ ​ ​ ​ ​ Office and other space ​ ​ ​ ​ ​ ​ General and administrative ​ ​ 1,044 ​ ​ 996 Voyage expenses ​ ​ 168 ​ ​ 168 ​ ​ ​ ​ ​ ​ ​ Short-term lease cost ​ ​ ​ ​ ​ ​ Vessel assets (1) ​ ​ ​ ​ ​ ​ Charter hire expenses ​ ​ 4,585 ​ ​ 10,769 ​ ​ ​ ​ ​ ​ ​ Office and other space ​ ​ ​ ​ ​ ​ General and administrative ​ ​ 29 ​ ​ 116 Voyage expenses ​ ​ — ​ ​ 52 Vessel expenses ​ ​ — ​ ​ 8 Total lease cost ​ $ 17,492 ​ $ 27,198 (1) Excludes vessels spot chartered-in under operating leases and employed in the Crude Tankers Lightering business for periods of less than one month each, totaling $1.2 million and $10.6 million for the years ended December 31, 2020 and 2019, respectively, including both lease and non-lease components.
Supplemental lease information	​ Supplemental cash flow information related to leases was as follows: ​ ​ ​ ​ ​ ​ ​ ​ (Dollars in thousands) ​ ​ 2020 ​ ​ 2019 Cash paid for amounts included in the measurement of lease liabilities ​ ​ ​ ​ ​ ​ Operating cash flows used for operating leases ​ $ 12,878 ​ $ 16,178 ​ Supplemental balance sheet information related to leases was as follows: ​ ​ ​ ​ ​ ​ ​ ​ (Dollars in thousands) ​ December 31, 2020 ​ December 31, 2019 Operating lease right-of-use assets ​ $ 21,588 ​ $ 33,718 ​ ​ ​ ​ ​ ​ ​ Current portion of operating lease liabilities ​ $ (8,867) ​ $ (12,958) Long-term operating lease liabilities ​ ​ (10,253) ​ ​ (17,953) Total operating lease liabilities ​ $ (19,120) ​ $ (30,911) ​ ​ ​ ​ ​ ​ ​ Weighted average remaining lease term - operating leases ​ ​ 2.75 years ​ ​ 3.24 years Weighted average discount rate - operating leases ​ ​ 7.21% ​ ​ 7.16%
Schedule of lease maturity receivables	​ ​ ​ ​ ​ ​ ​ (Dollars in thousands) ​ Amount ​ Revenue Days 2021 ​ $ 28,856 ​ 1,053 2022 ​ ​ 16,425 ​ 365 2023 ​ ​ 3,195 ​ 71 Future minimum revenues ​ $ 48,476 ​ 1,489
Office Space And Lightering Workboat Dock Space [Member]
Lease [Abstract]
Schedule of lease maturity payments	​ Payments of lease liabilities for office and other space as of December 31, 2020 are as follows: ​ ​ ​ ​ ​ (Dollars in thousands) ​ ​ Amount 2021 ​ $ 936 2022 ​ ​ 273 2023 ​ ​ 229 2024 ​ ​ 178 Total lease payments ​ ​ 1,616 less imputed interest ​ ​ (103) Total operating lease liabilities ​ $ 1,513
Bareboat Charters-In [Member]
Lease [Abstract]
Schedule of lease maturity payments	Payments of lease liabilities and related number of operating days under these operating leases as of December 31, 2020 are as follows ​ Bareboat Charters-in ​ ​ ​ ​ ​ ​ (Dollars in thousands) ​ Amount ​ Operating Days 2021 ​ $ 6,278 ​ 730 2022 ​ ​ 6,278 ​ 730 2023 ​ ​ 4,532 ​ 556 Total lease payments ​ ​ 17,088 ​ 2,016 less imputed interest ​ ​ (1,608) ​ ​ Total operating lease liabilities ​ $ 15,480 ​ ​
Time Charters-In [Member]
Lease [Abstract]
Schedule of lease maturity payments	Time Charters-in ​ ​ ​ ​ ​ ​ (Dollars in thousands) ​ Amount ​ Operating Days 2021 ​ $ 2,170 ​ 408 Total lease payments (lease component only) ​ ​ 2,170 ​ 408 less imputed interest ​ ​ (43) ​ ​ Total operating lease liabilities ​ $ 2,127 ​ ​

PENSION AND OTHER POSTRETIREM_2

PENSION AND OTHER POSTRETIREMENT BENEFIT PLANS (Tables)	12 Months Ended
	Dec. 31, 2020
Pension and Other Postretirement Benefit Plans [Abstract]
Schedule of Benefit Obligations in Excess of Fair Value of Plan Assets	Information with respect to the Scheme for which INSW uses a December 31 measurement date, is as follows: ​ ​ ​ ​ ​ ​ ​ ​ (Dollars in thousands) ​ December 31, 2020 ​ December 31, 2019 Change in benefit obligation: ​ ​ ​ ​ ​ ​ Benefit obligation at beginning of year ​ $ 27,481 ​ $ 23,814 Interest cost on benefit obligation ​ ​ 525 ​ ​ 657 Actuarial losses ​ ​ 2,202 ​ ​ 2,761 Benefits paid ​ ​ (875) ​ ​ (820) Foreign exchange losses ​ ​ 943 ​ ​ 1,069 Benefit obligation at year end ​ ​ 30,276 ​ ​ 27,481 ​ ​ ​ ​ ​ ​ ​ Change in plan assets: ​ ​ ​ ​ ​ ​ Fair value of plan assets at beginning of year ​ ​ 26,994 ​ ​ 22,785 Actual return on plan assets ​ ​ 3,427 ​ ​ 3,341 Employer contributions ​ ​ 664 ​ ​ 639 Benefits paid ​ ​ (875) ​ ​ (820) Foreign exchange gains ​ ​ 1,009 ​ ​ 1,049 Fair value of plan assets at year end ​ ​ 31,219 ​ ​ 26,994 Funded/(unfunded) status at December 31 ​ $ 943 ​ $ (487)
Schedule of Net Benefit Costs	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (Dollars in thousands) ​ ​ 2020 ​ ​ 2019 ​ ​ 2018 Components of expense: ​ ​ ​ ​ ​ ​ ​ ​ ​ Interest cost on benefit obligation ​ $ 525 ​ $ 657 ​ $ 707 Expected return on plan assets ​ ​ (1,018) ​ ​ (1,017) ​ ​ (1,029) Amortization of prior-service costs ​ ​ 75 ​ ​ 74 ​ ​ 71 Recognized net actuarial loss ​ ​ 310 ​ ​ 315 ​ ​ 388 Recognized settlement loss ​ ​ — ​ ​ — ​ ​ 1,442 Net periodic benefit cost ​ $ (108) ​ $ 29 ​ $ 1,579
Schedule of Effect of One-Percentage-Point Change in Assumed Health Care Cost Trend Rates	The weighted-average assumptions used to determine benefit obligations follow: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2020 ​ December 31, 2019 Discount rate ​ ​ 1.20% ​ ​ 2.00%
Schedule of Assumptions Used	The weighted-average assumptions used to determine net periodic benefit costs follow: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2020 ​ ​ 2019 ​ ​ 2018 Discount rate ​ ​ 2.00% ​ ​ 2.80% ​ ​ 2.40% Expected (long-term) return on plan assets ​ ​ 3.89% ​ ​ 4.46% ​ ​ 3.85% Rate of future compensation increases ​ ​ - ​ ​ - ​ ​ -
Schedule of Expected Benefit Payments	Expected benefit payments are as follows: ​ ​ ​ ​ ​ (Dollars in thousands) ​ Pension benefits 2021 ​ $ 865 2022 ​ ​ 866 2023 ​ ​ 895 2024 ​ ​ 1,022 2025 ​ ​ 1,126 Years 2026-2030 ​ ​ 5,452 ​ ​ $ 10,226
Schedule of Changes in Fair Value of Plan Assets	The fair values of the Company’s pension plan assets at December 31, 2020, by asset category are as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (Dollars in thousands) ​ Fair Value ​ Level 1 ​ Level 2 (1) Cash and cash equivalents ​ $ 757 ​ $ 757 ​ $ — Managed funds ​ ​ 30,462 ​ ​ — ​ ​ 30,462 Total ​ $ 31,219 ​ $ 757 ​ $ 30,462 (1) Quoted prices for the managed funds are not available from an active market source since such investments are pooled investment funds. The unitized pooled investment vehicles have been valued at the latest available bid price or single price provided by the pooled investment manager. Shares in other pooled arrangements have been valued at the latest available net asset value, determined in accordance with fair value principles, provided by the pooled investment manager. ​ ​

OTHER EXPENSE (Tables)

OTHER EXPENSE (Tables)	12 Months Ended
	Dec. 31, 2020
OTHER EXPENSE [Abstract]
Schedule of Other Nonoperating Expense	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (Dollars in thousands) ​ ​ 2020 ​ ​ 2019 ​ ​ 2018 Investment income - interest ​ $ 558 ​ $ 2,520 ​ $ 1,300 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net actuarial gain/(loss) on defined benefit pension plan ​ ​ 633 ​ ​ 628 ​ ​ (902) Write-off of deferred financing costs ​ ​ (13,073) ​ ​ (3,558) ​ ​ (2,400) Loss on extinguishment of debt ​ ​ (1,197) ​ ​ (1,100) ​ ​ (1,295) Other ​ ​ 262 ​ ​ 567 ​ ​ (418) ​ ​ $ (12,817) ​ $ (943) ​ $ (3,715)

2020 AND 2019 QUARTERLY RESUL_2

2020 AND 2019 QUARTERLY RESULTS OF OPERATIONS (UNAUDITED) (Table)	12 Months Ended
	Dec. 31, 2020
2020 AND 2019 QUARTERLY RESULTS OF OPERATIONS [Abstract]
Schedule of Quarterly Financial Information	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Selected Financial Data for the Quarter Ended ​ March 31, ​ June 30, ​ Sept. 30, ​ Dec. 31, 2020 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Shipping revenues ​ $ 125,337 ​ $ 139,725 ​ $ 99,883 ​ $ 56,703 Gain/(loss) on disposal of vessels and other property, including impairments (1) ​ ​ 2,804 ​ ​ (4,134) ​ ​ (12,834) ​ ​ (85,923) Income/(loss) from vessel operations ​ ​ 53,349 ​ ​ 67,892 ​ ​ 16,832 ​ ​ (98,193) Equity in income of affiliated companies (1) ​ ​ 5,111 ​ ​ 5,205 ​ ​ 5,356 ​ ​ (11,553) Interest expense ​ ​ (12,009) ​ ​ (8,881) ​ ​ (7,999) ​ ​ (7,823) Income tax provision ​ ​ — ​ ​ (1) ​ ​ — ​ ​ — Net income/(loss) ​ ​ 33,019 ​ ​ 64,358 ​ ​ 13,981 ​ ​ (116,889) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Basic and diluted net income/(loss) per share ​ $ 1.13 ​ $ 2.26 ​ $ 0.50 ​ $ (4.18) (1) Refer to Note 5, “Vessels, Deferred Drydock and Other Property” and Note 6, “Equity Method Investments,” respectively, for further information on a $85.9 million impairment charge recorded during the fourth quarter of 2020 and the Company’s $16.4 million share of a non-cash deferred tax provision recorded by the FSO Joint Venture during the fourth quarter of 2020. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Selected Financial Data for the Quarter Ended ​ March 31, ​ June 30, ​ Sept. 30, ​ Dec. 31, 2019 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Shipping revenues ​ $ 101,874 ​ $ 69,010 ​ $ 71,278 ​ $ 124,022 Gain/(loss) on disposal of vessels and other property ​ ​ 48 ​ ​ (1,548) ​ ​ 1,472 ​ ​ (280) Income/(loss) from vessel operations ​ ​ 19,324 ​ ​ (7,934) ​ ​ (2,843) ​ ​ 46,621 Equity in income of affiliated companies ​ ​ 8,070 ​ ​ 8,015 ​ ​ 8,474 ​ ​ (13,346) Interest expense ​ ​ (17,533) ​ ​ (17,443) ​ ​ (17,010) ​ ​ (14,281) Income tax provision ​ ​ — ​ ​ — ​ ​ — ​ ​ (1) Net income/(loss) ​ ​ 10,897 ​ ​ (16,523) ​ ​ (11,095) ​ ​ 15,891 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Basic and diluted net income/(loss) per share ​ $ 0.37 ​ $ (0.57) ​ $ (0.38) ​ $ 0.54

DESCRIPTION OF BUSINESS AND B_2

DESCRIPTION OF BUSINESS AND BASIS OF PRESENTATION (Narrative) (Details)	3 Months Ended	12 Months Ended
	Dec. 31, 2020property	Dec. 31, 2020segmentproperty
Property, Plant and Equipment [Line Items]
Number of vessels in fleet	36	36
Number of vessels owned (including joint ventures)	33	33
Number of reportable segments | segment		2
Number of vessels marketed to be sold	2
FSO Joint Venture [Member]
Property, Plant and Equipment [Line Items]
Number of vessels owned (including joint ventures)	2	2

SUMMARY SIGNIFICANT ACCOUNTING

SUMMARY SIGNIFICANT ACCOUNTING POLICIES (Narrative) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2020USD ($)$ / item	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)
Summary Of Significant Accounting Policies [Line Items]
Allowance for doubtful accounts receivable	$ 55	$ 1,245
Provision for credit losses, net	(71)	1,245
Amortization of financing costs	2,800	4,800	$ 3,900
Defined benefit plan, interest cost	525	657	707
Restricted cash and cash equivalents, noncurrent	$ 16,287	60,572
Debt instrument, interest rate, stated percentage	10.75%
Repayments of advances from affiliated companies	$ 7,456	4,195	100,780
Proceeds from Insurance Settlement, Operating Activities	$ 5,238	2,179	5,436
Credit losses outstanding additional period	180 days
Credit losses historical period	5 years
Collateralized basis percentage benchmark used in determining borrowing rate	100.00%
Vessel/Fleet [Member]
Summary Of Significant Accounting Policies [Line Items]
Property, plant and equipment, useful life	25 years
Property, plant and equipment salvage, value per ton | $ / item	300
Interest costs capitalized	$ 0	$ 0	$ 0
Other Property [Member] | Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Property, plant and equipment, useful life	3 years
Other Property [Member] | Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Property, plant and equipment, useful life	7 years
Drydock [Member] | Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Amortization period for deferred costs	2 years 6 months
Drydock [Member] | Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Amortization period for deferred costs	5 years
Accounts Receivable [Member]
Summary Of Significant Accounting Policies [Line Items]
Concentration risk, percentage		88.00%
INSW Facilities [Member] | Revolving Credit Facility [Member]
Summary Of Significant Accounting Policies [Line Items]
Deferred finance costs, gross		$ 300
2017 Term Loan Facility, Sinosure Credit Facility, ABN Term Loan Facility, 8.5% Senior Notes and 10.75% Subordinated Notes [Member] | Term Loan [Member]
Summary Of Significant Accounting Policies [Line Items]
Deferred finance costs, gross		$ 16,300
Core Term Loan Facility, Core Transition Facility, Sinosure Credit Facility and 8.5% Senior Notes [Member]
Summary Of Significant Accounting Policies [Line Items]
Deferred finance costs, gross	$ 6,900
10.75% Subordinated Notes [Member]
Summary Of Significant Accounting Policies [Line Items]
Debt instrument, interest rate, stated percentage	10.75%	10.75%
8.5% Senior Notes [Member]
Summary Of Significant Accounting Policies [Line Items]
Debt instrument, interest rate, stated percentage	8.50%	8.50%
2020 Debt Facilities [Member]
Summary Of Significant Accounting Policies [Line Items]
Deferred finance costs, gross	$ 7,300
Core Revolving Facility [Member] | Term Loan [Member]
Summary Of Significant Accounting Policies [Line Items]
Deferred finance costs, gross	800
Core Revolving Facility [Member] | Revolving Credit Facility [Member]
Summary Of Significant Accounting Policies [Line Items]
Deferred finance costs, gross	$ 800

SUMMARY SIGNIFICANT ACCOUNTIN_2

SUMMARY SIGNIFICANT ACCOUNTING POLICIES (Activity for allowance for credit losses) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES [Abstract]
Balance Beginning	$ 1,245
Provision for expected credit losses	58	$ 1,245
Write-offs charged against the allowance	(1,119)
Recoveries of amounts previously written off	(129)
Balance Ending	$ 55	$ 1,245

EARNINGS PER COMMON SHARE (Narr

EARNINGS PER COMMON SHARE (Narrative) (Details) - shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share, amount	962,205	746,616	523,544
Dilutive awards	0	0	0
Restricted Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Participating securities allocated a portion of income	48,229	48,014	42,449
Restricted Stock Units (RSUs) [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potentially dilutive securities	233,833
Employee Stock Option [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potentially dilutive securities	670,624

EARNINGS PER COMMON SHARE (Reco

EARNINGS PER COMMON SHARE (Reconciliation of Net Income) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
EARNINGS PER COMMON SHARE [Abstract]
Common Stockholders									$ (5,544)	$ (830)	$ (88,940)
Participating securities									13
Net loss	$ (116,889)	$ 13,981	$ 64,358	$ 33,019	$ 15,891	$ (11,095)	$ (16,523)	$ 10,897	$ (5,531)	$ (830)	$ (88,940)

BUSINESS AND SEGMENT REPORTIN_2

BUSINESS AND SEGMENT REPORTING (Reportable Segments Information) (Details) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020USD ($)	Sep. 30, 2020USD ($)	Jun. 30, 2020USD ($)	Mar. 31, 2020USD ($)	Dec. 31, 2019USD ($)	Sep. 30, 2019USD ($)	Jun. 30, 2019USD ($)	Mar. 31, 2019USD ($)	Dec. 31, 2020USD ($)segment	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments | segment									2
Revenues, services									$ 421,648	$ 366,184	$ 270,361
Depreciation and amortization									74,343	75,653	72,428
Loss/(gain) on disposal of vessels and other property, including impairments	$ 85,923	$ 12,834	$ 4,134	$ (2,804)	$ 280	$ (1,472)	$ 1,548	$ (48)	100,087	308	19,680
Adjusted income/(loss) from vessel operations									169,175	83,549	(9,241)
Equity in income/(loss) of affiliated companies	(11,553)	$ 5,356	$ 5,205	$ 5,111	(13,346)	$ 8,474	$ 8,015	$ 8,070	4,119	11,213	29,432
Investments in and advances to affiliated companies	141,924				153,292				141,924	153,292	268,322
Adjusted total assets	1,366,332				1,597,694				1,366,332	1,597,694	1,726,437
Expenditures for vessels and vessel improvements									50,049	36,607	148,946
Payments for drydocking									25,642	19,546	4,520
Time Charter Equivalent Services [Member]
Segment Reporting Information [Line Items]
Revenues, services									402,005	339,919	243,100
International Crude Tankers Segment [Member]
Segment Reporting Information [Line Items]
Revenues, services									334,765	285,356	202,396
Depreciation and amortization									57,980	59,387	54,431
Loss/(gain) on disposal of vessels and other property, including impairments									44,330	82	22,992
Adjusted income/(loss) from vessel operations									144,451	71,344	2,194
Equity in income/(loss) of affiliated companies									4,119	19,383	19,582
Investments in and advances to affiliated companies	134,439				143,095				134,439	143,095	143,789
Adjusted total assets	1,112,342				1,284,631				1,112,342	1,284,631	1,285,433
Expenditures for vessels and vessel improvements									27,858	33,384	146,322
Payments for drydocking									20,313	16,997	4,121
International Crude Tankers Segment [Member] | Time Charter Equivalent Services [Member]
Segment Reporting Information [Line Items]
Revenues, services									318,588	259,517	175,524
International Product Carriers Segment [Member]
Segment Reporting Information [Line Items]
Revenues, services									86,883	80,828	67,965
Depreciation and amortization									16,269	16,152	17,862
Loss/(gain) on disposal of vessels and other property, including impairments									55,757	226	(3,312)
Adjusted income/(loss) from vessel operations									24,818	12,319	(12,002)
Investments in and advances to affiliated companies	7,485				10,197				7,485	10,197	12,321
Adjusted total assets	$ 253,990				$ 313,063				253,990	313,063	328,792
Expenditures for vessels and vessel improvements									22,191	3,223	2,624
Payments for drydocking									5,329	2,549	399
International Product Carriers Segment [Member] | Time Charter Equivalent Services [Member]
Segment Reporting Information [Line Items]
Revenues, services									83,417	80,402	67,576
Other Segment [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization									94	114	135
Adjusted income/(loss) from vessel operations									$ (94)	(114)	567
Equity in income/(loss) of affiliated companies										$ (8,170)	9,850
Investments in and advances to affiliated companies											112,212
Adjusted total assets											$ 112,212

BUSINESS AND SEGMENT REPORTIN_3

BUSINESS AND SEGMENT REPORTING (Reconciliation of Time Charter Revenue to Shipping Revenues) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Revenues, services	$ 421,648	$ 366,184	$ 270,361
Add: Voyage expenses	19,643	26,265	27,261
Time Charter Equivalent Services [Member]
Revenues, services	$ 402,005	$ 339,919	$ 243,100

BUSINESS AND SEGMENT REPORTIN_4

BUSINESS AND SEGMENT REPORTING (Reconciliation of Income/(Loss) from Vessel Operations to Loss Before Reorganization) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Total adjusted income/(loss) from vessel operations of all segments									$ 169,175	$ 83,549	$ (9,241)
General and administrative expenses									(29,047)	(26,798)	(24,304)
Provision for credit losses									71	(1,245)
Third-party debt modification fees									(232)	(30)	(1,306)
Loss on disposal of vessels and other property, including impairments	$ (85,923)	$ (12,834)	$ (4,134)	$ 2,804	$ (280)	$ 1,472	$ (1,548)	$ 48	(100,087)	(308)	(19,680)
Consolidated income/(loss) from vessel operations	(98,193)	16,832	67,892	53,349	46,621	(2,843)	(7,934)	19,324	39,880	55,168	(54,531)
Equity in income/(loss) of affiliated companies	(11,553)	5,356	5,205	5,111	(13,346)	8,474	8,015	8,070	4,119	11,213	29,432
Other income/(expense)									(12,817)	(943)	(3,715)
Interest expense	$ (7,823)	$ (7,999)	$ (8,881)	$ (12,009)	$ (14,281)	$ (17,010)	$ (17,443)	$ (17,533)	(36,712)	(66,267)	(60,231)
Loss before income taxes									(5,530)	(829)	(89,045)
Vessel Operations [Member]
Total adjusted income/(loss) from vessel operations of all segments									169,175	83,549	(9,241)
General and administrative expenses									(29,047)	(26,798)	(24,304)
Provision for credit losses									71	(1,245)
Third-party debt modification fees									(232)	(30)	(1,306)
Loss on disposal of vessels and other property, including impairments									(100,087)	(308)	(19,680)
Consolidated income/(loss) from vessel operations									39,880	55,168	(54,531)
Equity in income/(loss) of affiliated companies									4,119	11,213	29,432
Other income/(expense)									(12,817)	(943)	(3,715)
Interest expense									(36,712)	(66,267)	(60,231)
Loss before income taxes									$ (5,530)	$ (829)	$ (89,045)

BUSINESS AND SEGMENT REPORTIN_5

BUSINESS AND SEGMENT REPORTING (Reconciliation of Assets of Segments to Consolidated Amounts) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Segment Reporting Information [Line Items]
Adjusted total assets	$ 1,366,332	$ 1,597,694	$ 1,726,437
Cash and cash equivalents	199,390	89,671
Restricted cash	16,287	60,572
Other unallocated amounts	4,530	5,564
Total assets	$ 1,586,539	$ 1,753,501
Other Segment [Member]
Segment Reporting Information [Line Items]
Adjusted total assets			$ 112,212

BUSINESS AND SEGMENT REPORTIN_6

BUSINESS AND SEGMENT REPORTING (Additional Information) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Segment Reporting Information [Line Items]
Vessels Deferred Dry Dock and Other Property	$ 1,144,548	$ 1,315,641	$ 1,347,568
International Crude Tankers Segment [Member]
Segment Reporting Information [Line Items]
Vessels Deferred Dry Dock and Other Property	919,974	1,051,848	1,057,994
International Product Carriers Segment [Member]
Segment Reporting Information [Line Items]
Vessels Deferred Dry Dock and Other Property	224,507	263,651	289,317
Other Segment [Member]
Segment Reporting Information [Line Items]
Vessels Deferred Dry Dock and Other Property	$ 67	$ 142	$ 257

VESSELS, DEFERRED DRYDOCK AND_3

VESSELS, DEFERRED DRYDOCK AND OTHER PROPERTY (Narrative) (Details)

Jun. 14, 2018USD ($)company

Jun. 14, 2018USD ($)

Oct. 31, 2020USD ($)

Oct. 31, 2020property

Oct. 31, 2020

Jul. 31, 2018property

Jun. 30, 2018USD ($)property

Dec. 31, 2020USD ($)property

Sep. 30, 2020USD ($)

Jun. 30, 2020USD ($)

Sep. 30, 2018USD ($)property

Dec. 31, 2020USD ($)property

Dec. 31, 2019USD ($)

Dec. 31, 2018USD ($)property

Oct. 31, 2018USD ($)

Property, Plant and Equipment [Line Items]

Impairment of long-lived assets to be disposed of

$ 16,400,000

Impairment of long-lived assets held-for-use

$ 85,900,000

$ 103,022,000

$ 19,037,000

Gain (loss) on disposition of property

2,935,000

$ (308,000)

$ (643,000)

Payable associated with acquisition of assets

$ 20,900,000

Number of vessels marketed to be sold | property

2

Number of vessels with impairment triggering events | property

3

Loss on contract termination

$ 1,600,000

Number of vessels used as collateral on debt | property

20

Vessel/Fleet [Member]

Property, Plant and Equipment [Line Items]

Impairment of long-lived assets to be disposed of

$ 341,065,000

$ 58,021,000

Very Large Crude Carrier [Member]

Property, Plant and Equipment [Line Items]

Impairment of long-lived assets to be disposed of

$ 14,200,000

Number of vessels with impairment triggering events | property

1

1

1

2 VLCCs to be sold [Member]

Property, Plant and Equipment [Line Items]

Impairment of long-lived assets held-for-use

$ 11,700,000

Number of vessels marketed to be sold

2

2

2

Number of vessels with impairment triggering events | property

2

2

Probability percentage of property being sold

100.00%

25.00%

1 of 2 VLCCs to be sold [Member]

Property, Plant and Equipment [Line Items]

Impairment of long-lived assets to be disposed of

$ 5,500,000

1 VLCC with Unrecoverable Carrying Value [Member]

Property, Plant and Equipment [Line Items]

Number of vessels marketed to be sold | property

1

Very Large Crude Carrier Cost To Sell [Member]

Property, Plant and Equipment [Line Items]

Impairment of long-lived assets to be disposed of

$ 400,000

Very Large Crude Carrier Operational Costs [Member]

Property, Plant and Equipment [Line Items]

Impairment of long-lived assets to be disposed of

$ 1,800,000

1-MR Vessel [Member]

Property, Plant and Equipment [Line Items]

Impairment of long-lived assets to be disposed of

$ 1,700,000

Number of vessels with impairment triggering events | property

1

Probability percentage of property being sold

50.00%

6 VLCC [Member]

Property, Plant and Equipment [Line Items]

Payments to acquire equipment

$ 120,000,000

$ 120,000,000

Purchase agreement, purchase amount

434,000,000

434,000,000

Number of vessels acquired

$ 6

Number of businesses acquired | company

6

One 2015 Built VLCC [Member]

Property, Plant and Equipment [Line Items]

Number of vessels acquired

$ 1

Five 2015 Built VLCC [Member]

Property, Plant and Equipment [Line Items]

Number of vessels acquired

5

Certain Vessels Sold [Member]

Property, Plant and Equipment [Line Items]

Gain (loss) on disposition of property

(300,000)

$ 600,000

1 Panamax Vessel [Member]

Property, Plant and Equipment [Line Items]

Impairment of long-lived assets to be disposed of

$ 900,000

Number of vessels with impairment triggering events | property

1

Probability percentage of property being sold

100.00%

LR1 Vessel [Member]

Property, Plant and Equipment [Line Items]

Purchase agreement, purchase amount

18,800,000

Number of vessels with impairment triggering events | property

2

2

2 Aframaxes

Property, Plant and Equipment [Line Items]

Number of vessels marketed to be sold | property

2

Number of vessels with impairment triggering events | property

2

2

Probability percentage of property being sold

50.00%

1 VLCC and 1 MR Vessel

Property, Plant and Equipment [Line Items]

Number of vessels marketed to be sold | property

2

2 Aframaxes and 2 VLCC Vessels

Property, Plant and Equipment [Line Items]

Gain (loss) on disposition of property

$ 4,500,000

MR Vessels

Property, Plant and Equipment [Line Items]

Number of vessels with impairment triggering events | property

4

4

1 VLCC, 2 LR1s and 4 MR Vessels

Property, Plant and Equipment [Line Items]

Impairment of long-lived assets held-for-use

$ 85,900,000

Aframaxes [Member]

Property, Plant and Equipment [Line Items]

Number of vessels with impairment triggering events | property

1

1

Sinosure Credit Facility [Member]

Property, Plant and Equipment [Line Items]

Debt instrument, collateral amount

$ 429,500,000

Number of vessels used as collateral on debt | property

6

Sinosure Credit Facility [Member] | 6 VLCC [Member]

Property, Plant and Equipment [Line Items]

Purchase agreement, purchase amount

434,000,000

$ 434,000,000

Number of vessels acquired

$ 6

Core Term Loan Facility [Member] | Term Loan [Member]

Property, Plant and Equipment [Line Items]

Debt instrument, collateral amount

$ 551,300,000

$ 551,300,000

Number of vessels used as collateral on debt | property

14

VESSELS, DEFERRED DRYDOCK AND_4

VESSELS, DEFERRED DRYDOCK AND OTHER PROPERTY (Vessels and Other Property) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Net, Total	$ 1,108,214	$ 1,292,516
Vessel/Fleet and Other Property [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Net, Total	1,108,214	1,292,516
Vessel/Fleet [Member]
Property, Plant and Equipment [Line Items]
Cost	1,287,688	1,650,670	$ 1,629,647	$ 1,404,360
Accumulated Depreciation	(182,148)	(361,088)	(301,885)	(302,087)
Property, Plant and Equipment, Net, Total	1,105,540	1,289,582	$ 1,327,762	$ 1,102,273
Other Property [Member]
Property, Plant and Equipment [Line Items]
Cost	6,610	6,714
Accumulated Depreciation	(3,936)	(3,780)
Property, Plant and Equipment, Net, Total	$ 2,674	$ 2,934

VESSELS, DEFERRED DRYDOCK AND_5

VESSELS, DEFERRED DRYDOCK AND OTHER PROPERTY (Breakdown of Vessel Carrying Value) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2020USD ($)item	Dec. 31, 2019USD ($)item	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)
Property, Plant and Equipment [Line Items]
Net Carrying Value	$ 1,108,214	$ 1,292,516
Vessel/Fleet [Member]
Property, Plant and Equipment [Line Items]
Cost	1,287,688	1,650,670	$ 1,629,647	$ 1,404,360
Accumulated Depreciation	(182,148)	(361,088)	(301,885)	(302,087)
Net Carrying Value	$ 1,105,540	$ 1,289,582	$ 1,327,762	$ 1,102,273
Average Vessel Age	9 years	9 years 4 months 24 days
Number of owned vessels | item	31	34
International Crude Tankers Segment [Member]
Property, Plant and Equipment [Line Items]
Cost	$ 1,047,267	$ 1,301,317
Accumulated Depreciation	(155,450)	(271,106)
Net Carrying Value	$ 891,817	$ 1,030,211
Average Vessel Age	8 years 9 months 18 days	9 years 4 months 24 days
Number of owned vessels | item	21	25
Property, plant and equipment, fair value	$ 134,035
International Crude Tankers Segment [Member] | VLCCs (included ULCC) [Member]
Property, Plant and Equipment [Line Items]
Cost	839,542	$ 1,028,760
Accumulated Depreciation	(131,862)	(236,217)
Net Carrying Value	$ 707,680	$ 792,543
Average Vessel Age	7 years 10 months 24 days	8 years 7 months 6 days
Number of owned vessels | item	11	13
International Crude Tankers Segment [Member] | Aframaxes [Member]
Property, Plant and Equipment [Line Items]
Cost	$ 32,395	$ 96,038
Accumulated Depreciation	(1,378)	(19,659)
Net Carrying Value	$ 31,017	$ 76,379
Average Vessel Age	7 years 6 months	14 years 1 month 6 days
Number of owned vessels | item	1	3
International Crude Tankers Segment [Member] | Suzemax [Member]
Property, Plant and Equipment [Line Items]
Cost	$ 117,338	$ 117,338
Accumulated Depreciation	(14,099)	(10,007)
Net Carrying Value	$ 103,239	$ 107,331
Average Vessel Age	3 years 4 months 24 days	2 years 4 months 24 days
Number of owned vessels | item	2	2
International Crude Tankers Segment [Member] | Panamaxes [Member]
Property, Plant and Equipment [Line Items]
Cost	$ 57,992	$ 59,181
Accumulated Depreciation	(8,111)	(5,223)
Net Carrying Value	$ 49,881	$ 53,958
Average Vessel Age	18 years 2 months 12 days	17 years 2 months 12 days
Number of owned vessels | item	7	7
International Crude Tankers Segment [Member] | 10 VLCC and 1 Panamax Vessel
Property, Plant and Equipment [Line Items]
Net Carrying Value	$ 695,300
Property, plant and equipment, fair value	584,000
Pledged collateral market value over carrying value difference	111,300
International Product Carriers Segment [Member]
Property, Plant and Equipment [Line Items]
Cost	240,421	$ 349,353
Accumulated Depreciation	(26,698)	(89,982)
Net Carrying Value	$ 213,723	$ 259,371
Average Vessel Age	10 years 6 months	9 years 3 months 18 days
Number of owned vessels | item	10	9
Property, plant and equipment, fair value	$ 113,250
International Product Carriers Segment [Member] | MR Vessel [Member]
Property, Plant and Equipment [Line Items]
Cost	69,873	$ 167,421
Accumulated Depreciation		(52,848)
Net Carrying Value	$ 69,873	$ 114,573
Average Vessel Age	10 years	9 years
Number of owned vessels | item	4	4
International Product Carriers Segment [Member] | LR1 Vessel [Member]
Property, Plant and Equipment [Line Items]
Cost	$ 96,838	$ 108,251
Accumulated Depreciation	(9,279)	(22,420)
Net Carrying Value	$ 87,559	$ 85,831
Average Vessel Age	11 years 10 months 24 days	11 years
Number of owned vessels | item	5	4
International Product Carriers Segment [Member] | LR2 Vessel [Member]
Property, Plant and Equipment [Line Items]
Cost	$ 73,710	$ 73,681
Accumulated Depreciation	(17,419)	(14,714)
Net Carrying Value	$ 56,291	$ 58,967
Average Vessel Age	6 years 4 months 24 days	5 years 4 months 24 days
Number of owned vessels | item	1	1
International Product Carriers Segment [Member] | 1 LR2 and 3 LR1s Vessels
Property, Plant and Equipment [Line Items]
Net Carrying Value	$ 106,300
Property, plant and equipment, fair value	75,600
Pledged collateral market value over carrying value difference	$ 30,700

VESSELS, DEFERRED DRYDOCK AND_6

VESSELS, DEFERRED DRYDOCK AND OTHER PROPERTY (Vessel Activity) (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Vessel Cost
Impairment	$ (16,400)
Net Book Value
Property, Plant and Equipment, Net, Beginning Balance		$ 1,292,516
Property, Plant and Equipment, Net, Ending Balance		1,108,214	$ 1,292,516
Vessel/Fleet [Member]
Vessel Cost
Beginning Balance		1,650,670	1,629,647	$ 1,404,360
Purchases and vessel additions		48,436	38,138	459,608
Disposals		(70,353)	(17,115)	(176,300)
Impairment		(341,065)		(58,021)
Ending Balance		1,287,688	1,650,670	1,629,647
Accumulated Depreciation
Beginning Balance		(361,088)	(301,885)	(302,087)
Disposals		2,763	1,105	16,097
Depreciation		(61,866)	(60,308)	(56,711)
Impairment		238,043		40,816
Ending Balance		(182,148)	(361,088)	(301,885)
Net Book Value
Property, Plant and Equipment, Net, Beginning Balance		1,289,582	1,327,762	1,102,273
Property, Plant and Equipment, Net, Ending Balance		$ 1,105,540	$ 1,289,582	$ 1,327,762

VESSELS, DEFERRED DRYDOCK AND_7

VESSELS, DEFERRED DRYDOCK AND OTHER PROPERTY (Drydocking Activity) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
VESSELS, DEFERRED DRYDOCK AND OTHER PROPERTY [Abstract]
Beginning Balance	$ 23,125	$ 16,773	$ 30,528
Additions	27,835	21,086	5,616
Sub-total	50,960	37,859	36,144
Drydock amortization	(11,780)	(14,685)	(15,084)
Amount charged to loss/gain on sale of vessels	(2,846)	(49)	(4,287)
Ending Balance	$ 36,334	$ 23,125	$ 16,773

EQUITY METHOD INVESTMENTS (Narr

EQUITY METHOD INVESTMENTS (Narrative) (Details)	Oct. 07, 2019USD ($)	Apr. 26, 2018USD ($)	Mar. 29, 2018USD ($)	Oct. 31, 2020	Apr. 30, 2018USD ($)	May 31, 2017contractproperty	Nov. 30, 2004m³	Dec. 31, 2020USD ($)item	Sep. 30, 2020USD ($)	Jun. 30, 2020USD ($)	Mar. 31, 2020USD ($)	Dec. 31, 2019USD ($)	Sep. 30, 2019USD ($)	Jun. 30, 2019USD ($)	Mar. 31, 2019USD ($)	Dec. 31, 2020USD ($)itemcontract	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Apr. 16, 2020USD ($)
Schedule of Equity Method Investments [Line Items]
Number of joint ventures | item								2								2
Derivative, fixed interest rate																			0.50%
Derivative, notional amount																			$ 25,000,000
Accumulated other comprehensive gain (loss)								$ 32,613,000				$ 20,570,000				$ 32,613,000	$ 20,570,000
Income (loss) from equity method investments								(11,553,000)	$ 5,356,000	$ 5,205,000	$ 5,111,000	(13,346,000)	$ 8,474,000	$ 8,015,000	$ 8,070,000	4,119,000	11,213,000	$ 29,432,000
Investments in and advances to affiliated companies								141,924,000				153,292,000				$ 141,924,000	153,292,000
Gain on sale of equity method investment																	3,033,000
Release other comprehensive loss upon sale of investment in affiliated companies																	(21,615,000)
Number of arrangements reviewed for variable interest entity consideration | item																7
Income tax expense (benefit)												1,000				$ 1,000	1,000	$ (105,000)
FSO Term Loan [Member]
Schedule of Equity Method Investments [Line Items]
Long-term debt								45,200,000				69,600,000				45,200,000	69,600,000
Secured Debt [Member] | Financial Guarantee [Member] | FSO Revolver [Member] | Revolver Facility [Member] | Euro NV [Member]
Schedule of Equity Method Investments [Line Items]
Line of credit facility, maximum borrowing capacity								$ 110,000,000								$ 110,000,000
LNG and FSO Joint Ventures [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage								50.00%								50.00%
Number of joint ventures								2								2
LNG Joint Venture [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage	49.90%
Proceeds from divestiture of interest in joint venture	$ 123,000,000
Gain on sale of equity method investment	3,000,000
Release other comprehensive loss upon sale of investment in affiliated companies	$ 21,600,000
LNG Joint Venture [Member] | Liquid Natural Gas Carrier Vessel [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage							49.90%
Storage volume, per carrier | m³							216,200
Initial term of contract							25 years
FSO Joint Venture [Member]
Schedule of Equity Method Investments [Line Items]
Investments in and advances to affiliated companies								$ 128,800,000								$ 128,800,000
Number of contracts related to joint venture | contract						2										2
Number of vessels operated by joint venture | property						2
Contract service duration						5 years
Contract extension duration				10 years												10 years
Income tax expense (benefit)								16,400,000								$ 32,800,000
Guarantee facility extension period																10 years
FSO Joint Venture [Member] | FSO Term Loan [Member]
Schedule of Equity Method Investments [Line Items]
Guarantor obligations, maximum exposure, undiscounted								46,400,000								$ 46,400,000
Guarantor obligations, current carrying value								44,000								44,000
Minimum liquidity level, threshold amount					$ 50,000,000
Debt instrument covenant percentage of liquid assets to total indebtedness					5
Minimum cash, threshold amount, debt instrument covenant					$ 30,000,000
FSO Joint Venture [Member] | Interest Rate Swap [Member]
Schedule of Equity Method Investments [Line Items]
Derivative, notional amount								90,400,000				139,200,000				90,400,000	139,200,000
Derivative, fair value, asset (liability)								2,400,000				2,400,000				$ 2,400,000	2,400,000
Accumulated other comprehensive gain (loss)												$ 1,200,000					$ 1,200,000
FSO Joint Venture [Member] | Secured Debt [Member] | Revolver Facility [Member]
Schedule of Equity Method Investments [Line Items]
Debt instrument, basis spread on variable rate																2.00%
FSO Joint Venture [Member] | Secured Debt [Member] | FSO Term Loan [Member] | Medium-term Notes [Member]
Schedule of Equity Method Investments [Line Items]
Line of credit facility, maximum borrowing capacity			$ 110,000,000
FSO Joint Venture [Member] | Secured Debt [Member] | FSO Revolver [Member] | Revolving Credit Agreement [Member]
Schedule of Equity Method Investments [Line Items]
Line of credit facility, maximum borrowing capacity			110,000,000
Proceeds from long-term lines of credit		$ 110,000,000
Debt instrument, description of variable rate basis																based on three month, six month or twelve month LIBOR
Line of Credit Facility, Commitment Fee Percentage																0.70%
Line of credit facility, commitment fee percentage paid to affiliate																0.30%
FSO Joint Venture [Member] | Secured Debt [Member] | Financial Guarantee [Member] | FSO Term Loan [Member] | Medium-term Notes [Member]
Schedule of Equity Method Investments [Line Items]
Line of credit facility, maximum borrowing capacity								$ 110,000,000								$ 110,000,000
Proceeds from long-term lines of credit		$ 110,000,000
FSO Joint Venture [Member] | Secured Debt [Member] | FSO Loan Agreement [Member]
Schedule of Equity Method Investments [Line Items]
Line of credit facility, maximum borrowing capacity			$ 220,000,000
Debt instrument covenant debt service cover ratio			1.10
FSO Joint Venture [Member] | Secured Debt [Member] | Interest Rate Swap [Member] | Medium-term Notes [Member]
Schedule of Equity Method Investments [Line Items]
Derivative, fixed interest rate								4.858%								4.858%
Other Equity Method Investments [Member]
Schedule of Equity Method Investments [Line Items]
Investments in and advances to affiliated companies								$ 13,100,000								$ 13,100,000

EQUITY METHOD INVESTMENTS (Resu

EQUITY METHOD INVESTMENTS (Results of Operations of Equity Method Investments) (Details) - USD ($) $ in Thousands	Oct. 07, 2019	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Nov. 30, 2004
Shipping revenues		$ 56,703	$ 99,883	$ 139,725	$ 125,337	$ 124,022	$ 71,278	$ 69,010	$ 101,874	$ 421,648	$ 366,184	$ 270,361
Income/(loss) from vessel operations		(98,193)	16,832	67,892	53,349	46,621	(2,843)	(7,934)	19,324	39,880	55,168	(54,531)
Other income/(expense)										(12,817)	(943)	(3,715)
Interest expense		(7,823)	(7,999)	(8,881)	(12,009)	(14,281)	(17,010)	(17,443)	(17,533)	(36,712)	(66,267)	(60,231)
Income tax (provision)/benefit						(1)				(1)	(1)	105
Net loss		(116,889)	13,981	64,358	33,019	15,891	(11,095)	(16,523)	10,897	(5,531)	(830)	(88,940)
Gain on sale of equity method investment											3,033
Release other comprehensive loss upon sale of investment in affiliated companies											(21,615)
Equity in income of affiliated companies		$ (11,553)	$ 5,356	$ 5,205	$ 5,111	$ (13,346)	$ 8,474	$ 8,015	$ 8,070	4,119	11,213	29,432
Equity Method Investments [Member]
Shipping revenues										105,053	193,446	209,571
Ship operating expenses										58,858	103,499	112,541
Income/(loss) from vessel operations										46,195	89,947	97,030
Other income/(expense)										22	1,459	1,494
Interest expense										(6,571)	(32,752)	(40,676)
Income tax (provision)/benefit										(36,404)	(3,399)	(3,433)
Net loss										$ 3,242	$ 55,255	54,415
Equity method investment, ownership percentage		50.00%				50.00%				50.00%	50.00%
Equity in net income of affiliated companies, before consolidating and reconciling adjustments										$ 1,621	$ 27,606	27,187
Gain on sale of equity method investment										0	3,033	0
Release other comprehensive loss upon sale of investment in affiliated companies										0	(21,615)	0
Amortization on deferred gain on 2009 sale of TI Africa to FSO Joint Venture										2,385	2,395	2,395
Amortization of interest capitalized during vessel construction										0	(320)	(419)
Other										113	114	269
Equity in income of affiliated companies										$ 4,119	$ 11,213	$ 29,432
Minimum [Member] | Equity Method Investments [Member]
Equity method investment, ownership percentage						49.90%					49.90%	49.90%
Maximum [Member] | Equity Method Investments [Member]
Equity method investment, ownership percentage		50.00%				50.00%				50.00%	50.00%	50.00%
LNG Joint Venture [Member]
Equity method investment, ownership percentage	49.90%
Gain on sale of equity method investment	$ 3,000
Release other comprehensive loss upon sale of investment in affiliated companies	$ 21,600
LNG Joint Venture [Member] | Liquid Natural Gas Carrier Vessel [Member]
Equity method investment, ownership percentage													49.90%

EQUITY METHOD INVESTMENTS (Equi

EQUITY METHOD INVESTMENTS (Equity Method Investments Balance Sheet Schedule) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Oct. 07, 2019
Current assets	$ 256,834	$ 187,344
Net Carrying Value	1,108,214	1,292,516
Total Assets	1,586,539	1,753,501
Current liabilities	108,896	114,476
Long-term debt and other non-current liabilities	614,497	731,208
Total Liabilities and Equity	1,586,539	1,753,501
Other	262	567	$ (418)
Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures, Total	141,924	153,292
Equity Method Investments [Member]
Current assets	20,154	20,808
Net Carrying Value	490,093	523,802
Total Assets	510,247	544,610
Current liabilities	59,567	53,774
Long-term debt and other non-current liabilities	111,263	143,673
Equity	339,417	347,163
Total Liabilities and Equity	$ 510,247	$ 544,610
Percentage of ownership in equity investees	50.00%	50.00%
INSW share of affiliate's equity, before consolidating and reconciling adjustments	$ 169,708	$ 173,581
Advances from shareholders of FSO Joint Venture	16,665	23,216
Unamortized deferred gain on 2009 sale of TI Africa to FSO Africa, net	(27,156)	(29,503)
INSW guarantee for FSO Term Loan	44	264
Other	13,138	16,209
Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures, Total	141,924	153,292
LNG Joint Venture [Member]
Percentage of ownership in equity investees				49.90%
FSO Joint Venture [Member]
Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures, Total	128,800
FSO Joint Venture [Member] | Equity Method Investments [Member]
Impairment of equity method investments	(30,475)	$ (30,475)
Other Equity Method Investments [Member]
Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures, Total	$ 13,100

VARIABLE INTEREST ENTITIES (V_3

VARIABLE INTEREST ENTITIES (VIEs) (Narrative) (Details)	Dec. 31, 2020USD ($)item	Dec. 31, 2019USD ($)
Variable Interest Entity [Line Items]
Number of commercial pools	5
Number of joint ventures	2
Accounts receivable, net, current | $	$ 43,362,000	$ 83,845,000
LNG and FSO Joint Ventures [Member]
Variable Interest Entity [Line Items]
Number of joint ventures | $	2
Variable Interest Entity, Not Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Number of commercial pools	1
Number of joint ventures	2
Accounts receivable, net, current | $	$ 6,700,000

VARIABLE INTEREST ENTITIES (V_4

VARIABLE INTEREST ENTITIES (VIEs)) (Balance Sheet Carrying Amounts Related to VIEs) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Variable Interest Entity [Line Items]
Investments in Affiliated Companies	$ 141,924	$ 153,292	$ 268,322
Variable Interest Entity, Not Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Investments in Affiliated Companies	$ 132,902	$ 140,915

VARIABLE INTEREST ENTITIES (V_5

VARIABLE INTEREST ENTITIES (VIEs) (Comparison of Liability to Maximum Exposure to Loss) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Variable Interest Entity [Line Items]
Other Liabilities	$ 14,861	$ 1,489
Variable Interest Entity, Not Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Other Liabilities	44
Maximum Exposure to Loss	$ 179,291

DEBT (Schedule of Long-term Deb

DEBT (Schedule of Long-term Debt Instruments) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Jun. 30, 2018	Jun. 14, 2018	May 31, 2018
Debt Instrument [Line Items]
Less current portion	$ (61,483)	$ (70,350)
Long-term portion	$ 474,332	590,745
Debt instrument, interest rate, stated percentage	10.75%
2017 Debt Facilities [Member]
Debt Instrument [Line Items]
Long-term debt	$ 535,815	661,095
Less current portion	(61,483)	(70,350)
Long-term portion	474,332	590,745
INSW Facilities [Member]
Debt Instrument [Line Items]
Long-term debt	542,698
Sinosure Credit Facility [Member]
Debt Instrument [Line Items]
Long-term debt	244,243	267,443			$ 310,900
Unamortized discount and deferred finance costs	$ 1,884	$ 2,262
8.5% Senior Notes [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	8.50%	8.50%
10.75% Subordinated Notes [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	10.75%	10.75%
Term Loan [Member] | 2017 Debt Facilities [Member]
Debt Instrument [Line Items]
Long-term debt		$ 320,309
Unamortized discount and deferred finance costs	$ 11,211
Term Loan [Member] | ABN Term Loan Facility [Member]
Debt Instrument [Line Items]
Long-term debt		22,638
Unamortized discount and deferred finance costs		610
Term Loan [Member] | Core Term Loan Facility [Member]
Debt Instrument [Line Items]
Long-term debt	267,427
Unamortized discount and deferred finance costs	4,145
Senior Notes [Member] | 8.5% Senior Notes [Member]
Debt Instrument [Line Items]
Long-term debt	24,145	23,858
Unamortized discount and deferred finance costs	$ 855	$ 1,142
Debt instrument, interest rate, stated percentage	8.50%	8.50%	8.50%	8.50%		8.50%
Debt instrument, maturity date	Jun. 30, 2023
Subordinated Debt [Member] | 10.75% Subordinated Notes [Member]
Debt Instrument [Line Items]
Long-term debt		$ 26,847
Unamortized discount and deferred finance costs	$ 1,084
Debt instrument, interest rate, stated percentage	10.75%	10.75%	10.75%	10.75%

DEBT (2020 Debt Facilities) (Na

DEBT (2020 Debt Facilities) (Narrative) (Details) $ in Millions	Aug. 10, 2020USD ($)	May 15, 2020	Mar. 12, 2020	Mar. 11, 2020	Mar. 04, 2020USD ($)	Jan. 28, 2020USD ($)installment	Jan. 23, 2020USD ($)	Dec. 31, 2020USD ($)property	Dec. 31, 2019	Dec. 31, 2018USD ($)	Jun. 30, 2018
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage								10.75%
2020 Debt Facilities [Member]
Debt Instrument [Line Items]
Threshold leverage ratio						0.60%
Debt instrument, covenant compliance								The Company was in compliance with the financial and non-financial covenants under all of its debt facilities as of December 31, 2020.
2020 Debt Facilities [Member] | Vessel Seaways Mulan [Member]
Debt Instrument [Line Items]
Debt instrument covenants release of asset benchmark days				30 days
Debt instrument covenants release of asset, additional, benchmark days				30 days
2020 Debt Facilities [Member] | Secured Debt [Member]
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity							$ 390
2020 Debt Facilities [Member] | Side Letter Agreement [Member] | Vessel Seaways Mulan [Member]
Debt Instrument [Line Items]
Debt instrument covenants release of asset benchmark days		60 days	60 days
Debt instrument covenants release of asset, additional, benchmark days		30 days	30 days
Core Term Loan Facility and Core Revolving Facility [Member]
Debt Instrument [Line Items]
Applicable core margin							2.60%
Adjustments to applicable margin							0.025%
Adjustment threshold to applicable margin							0.025%
Number of vessels in fleet used as collateral | property								14
Core Term Loan Facility and Core Revolving Facility [Member] | Leverage Ratio Less Than 4.0 [Member]
Debt Instrument [Line Items]
Applicable core margin							2.40%
Threshold leverage ratio							4.00%
Decrease in applicable core margin							0.20%
Core Term Loan Facility and Core Revolving Facility [Member] | Leverage Ratio 6.0 Or Greater [Member]
Debt Instrument [Line Items]
Applicable core margin							2.80%
Threshold leverage ratio							6.00%
Core Term Loan Facility [Member]
Debt Instrument [Line Items]
Number of installments | installment						19
Periodic payment amount						$ 9.5
Frequency of payment						quarterly
Balloon payment						$ 120
Line Of Credit Accordion Amount							$ 100
Core Term Loan Facility [Member] | Term Loan [Member]
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity								$ 300
Line of credit facility, expiration period								5 years
Core Revolving Facility [Member]
Debt Instrument [Line Items]
Line of credit facility, expiration period								5 years
Repayments of debt					$ 20
Core Revolving Facility [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity						40		$ 40
Amount drawn						$ 20
Transition Facility [Member] | London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate							3.50%
Transition Facility [Member] | Term Loan [Member]
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity							$ 50
Repayments of debt	$ 40
Period after which interest rate can be increased							18 months
Number of installments | installment						10
Periodic payment amount						$ 5
Frequency of payment						quarterly
Number of vessels in fleet used as collateral | property								12
ABN Term Loan Facility [Member]
Debt Instrument [Line Items]
Repayments of debt						$ 23.2
Jefferies Finance
Debt Instrument [Line Items]
Repayments of debt						331.5
10.75% Subordinated Notes [Member]
Debt Instrument [Line Items]
Repurchase of debt						$ 27.9
Debt instrument, interest rate, stated percentage								10.75%	10.75%
10.75% Subordinated Notes [Member] | Subordinated Debt [Member]
Debt Instrument [Line Items]
Repurchase of debt										$ 2.1
Debt instrument, interest rate, stated percentage								10.75%	10.75%	10.75%	10.75%

DEBT (Sinosure Credit Facility)

DEBT (Sinosure Credit Facility) (Narrative) (Details)	Jun. 14, 2018USD ($)	Jun. 14, 2018USD ($)	Dec. 31, 2020USD ($)loan	Dec. 31, 2018USD ($)	Dec. 31, 2019USD ($)
6 VLCC [Member]
Debt Instrument [Line Items]
Purchase agreement, purchase amount	$ 434,000,000	$ 434,000,000
Payments to acquire equipment	120,000,000	120,000,000
Number of vessels acquired	$ 6
Debt instrument, term	144 months
Noncash or part noncash acquisition, debt assumed				$ 311,000,000
Sinosure Credit Facility [Member]
Debt Instrument [Line Items]
Long-term debt	$ 310,900,000	310,900,000	$ 244,243,000		$ 267,443,000
Debt instrument, basis spread on variable rate			2.00%
Debt instrument, maturity date, description			Each of the loans under the Sinosure Credit Facility will mature 144 months after its initial utilization date.
Debt instrument quarterly amortization payment percentage			1.66%
Number of loans | loan			6
Sinosure Credit Facility [Member] | 6 VLCC [Member]
Debt Instrument [Line Items]
Purchase agreement, purchase amount	434,000,000	$ 434,000,000
Number of vessels acquired	$ 6

DEBT (Debt Covenants) (Narrativ

DEBT (Debt Covenants) (Narrative) (Details) $ in Thousands	Jan. 28, 2020USD ($)	Dec. 31, 2020USD ($)	Jul. 01, 2020	Jun. 30, 2020	Dec. 31, 2019	Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2018	May 31, 2018
Debt instrument, interest rate, stated percentage		10.75%
2020 Debt Facilities [Member]
Debt instrument, covenant compliance		The Company was in compliance with the financial and non-financial covenants under all of its debt facilities as of December 31, 2020.
Minimum liquidity level, threshold amount	$ 50,000
Minimum liquidity level, threshold percentage of debt	5.00%
Threshold leverage ratio	0.60%
2020 Debt Facilities [Member] | Period From January 28, 2020 [Member]
Threshold ratio of consolidated EBITDA to consolidated cash interest expense	2.25
2020 Debt Facilities [Member] | Period Thereafter June 30, 2020 [Member]
Threshold ratio of consolidated EBITDA to consolidated cash interest expense	2.50
Core Term Loan Facility and Core Revolving Facility [Member]
Debt Instrument Covenant, Fair Market Value of the Core Collateral Vessels, Threshold Percentage Of Outstanding Principal Amount	135.00%
Transition Facility [Member]
Debt Instrument Covenant, Fair Market Value of the Core Collateral Vessels, Threshold Percentage Of Outstanding Principal Amount	175.00%
Sinosure Credit Facility [Member]
Debt instrument covenant minimum security coverage percentage of aggregate loan principal		135.00%
Debt instrument maximum consolidated leverage ratio		0.60%
Debt instrument minimum consolidated liquidity unrestricted consolidated cash and cash equivalents		$ 25,000
Debt instrument minimum consolidated liquidity total consolidated cash and cash equivalents		$ 50,000
Debt instrument covenant percentage of total indebtedness		5.00%
Debt instrument property aggregate covenant		$ 9,000
Debt instrument per piece of property covenant		$ 1,500
Debt instrument interest expense coverage ratio			2.50	2.25		2
8.5% Senior Notes [Member]
Debt instrument, interest rate, stated percentage		8.50%			8.50%
Senior Notes [Member] | 8.5% Senior Notes [Member]
Debt instrument covenant limitation on total borrowings percentage of total assets		70.00%
Debt instrument covenant net worth		$ 600,000
Debt instrument, interest rate, stated percentage		8.50%			8.50%		8.50%	8.50%	8.50%

DEBT (Senior and Subordinated N

DEBT (Senior and Subordinated Notes) (Narrative) (Details) - USD ($) $ in Thousands	May 31, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Jun. 30, 2018
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage		10.75%
Recapitalization costs		$ 232	$ 30	$ 1,306
Extinguishment of debt		422,699	110,000	62,069
Vessel Operations [Member]
Debt Instrument [Line Items]
Recapitalization costs		$ 232	$ 30	$ 1,306
8.5% Senior Notes [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage		8.50%	8.50%
10.75% Subordinated Notes [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage		10.75%	10.75%
Senior Notes [Member] | 8.5% Senior Notes [Member]
Debt Instrument [Line Items]
Debt instrument, face amount	$ 25,000
Debt instrument, interest rate, stated percentage	8.50%	8.50%	8.50%	8.50%	8.50%
Debt instrument, maturity date, description		notes due 2023
Proceeds from issuance of senior long-term debt	$ 23,500
Debt instrument, redemption price, percentage		100.00%
Debt instrument, maturity date		Jun. 30, 2023
Subordinated Debt [Member] | 10.75% Subordinated Notes [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage		10.75%	10.75%	10.75%	10.75%
Scenario, Plan [Member] | Senior Notes [Member] | 8.5% Senior Notes [Member]
Debt Instrument [Line Items]
Debt instrument, redemption price, percentage		101.00%

DEBT (Schedule of Interest Expe

DEBT (Schedule of Interest Expense and Interest Paid) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Jun. 30, 2018	May 31, 2018
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	10.75%
INSW Facilities [Member]
Debt Instrument [Line Items]
Interest expense, debt	$ 35,895	$ 64,982	$ 58,878
Interest paid, net	$ 30,586	$ 57,801	54,128
8.5% Senior Notes [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	8.50%	8.50%
10.75% Subordinated Notes [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	10.75%	10.75%
Core Revolving Facility [Member]
Debt Instrument [Line Items]
Interest expense, debt	$ 660	$ 0	0
Term Loan [Member] | Debt Facilities 2017 [Member]
Debt Instrument [Line Items]
Interest expense, debt	3,628	41,483	45,601
Interest paid, net	2,011	36,236	42,825
Term Loan [Member] | ABN Term Loan Facility [Member]
Debt Instrument [Line Items]
Interest expense, debt	107	1,716	1,024
Interest paid, net	156	1,504	795
Term Loan [Member] | Core Term Loan Facility [Member]
Debt Instrument [Line Items]
Interest expense, debt	13,542	0	0
Interest paid, net	12,024
Term Loan [Member] | Transition Facility [Member]
Debt Instrument [Line Items]
Interest expense, debt	1,518	0	0
Interest paid, net	1,183
Revolver Facility [Member] | Debt Facilities 2017 [Member]
Debt Instrument [Line Items]
Interest expense, debt	63	848	475
Interest paid, net	53	710	442
Revolver Facility [Member] | Core Revolving Facility [Member]
Debt Instrument [Line Items]
Interest paid, net	471
Senior Notes [Member] | 8.5% Senior Notes [Member]
Debt Instrument [Line Items]
Interest expense, debt	2,417	2,390	1,396
Interest paid, net	$ 2,130	$ 2,130	$ 1,250
Debt instrument, interest rate, stated percentage	8.50%	8.50%	8.50%	8.50%	8.50%
Subordinated Debt [Member] | 10.75% Subordinated Notes [Member]
Debt Instrument [Line Items]
Interest expense, debt	$ 276	$ 3,642	$ 2,032
Interest paid, net	$ 359	$ 3,021	$ 1,591
Debt instrument, interest rate, stated percentage	10.75%	10.75%	10.75%	10.75%
Revolving Credit Facility [Member] | Sinosure Credit Facility [Member]
Debt Instrument [Line Items]
Interest expense, debt	$ 13,684	$ 14,903	$ 8,350
Interest paid, net	$ 12,199	$ 14,200	$ 7,225

DEBT (Debt Modification, Repurc

DEBT (Debt Modification, Repurchases and Extinguishment) (Narrative) (Details) - USD ($) $ in Thousands	Oct. 08, 2019	Oct. 31, 2019	Jul. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Jan. 28, 2020	Jan. 23, 2020	Jun. 30, 2018	May 31, 2018
Debt Instrument [Line Items]
Write off of deferred debt issuance cost				$ 13,073	$ 3,558	$ 2,400
Gain (loss) on repurchase of debt instrument				(1,197)	(1,100)	(1,295)
Gain (Loss) on extinguishment of debt				(1,197)	(1,100)	(1,295)
Other income/(expense)				$ (12,817)	(943)	(3,715)
Debt instrument, interest rate, stated percentage				10.75%
(Gains) losses on repurchase and extinguishment of debt				$ 14,300
ABN Term Loan Facility and Sinosure Credit Facility and 8.50% Senior Notes and 10.75% Subordinated Notes [Member]
Debt Instrument [Line Items]
Debt Related Commitment Fees and Debt Issuance Costs						7,700
Deferred finance costs, gross						7,600
Payments of Debt Issuance Costs						100
ABN Term Loan Facility and Sinosure Credit Facility and 8.50% Senior Notes and 10.75% and 2017 Debt Facilities [Member]
Debt Instrument [Line Items]
Debt Related Commitment Fees and Debt Issuance Costs						14,600
2017 Debt Facilities [Member]
Debt Instrument [Line Items]
Gains (losses) on restructuring of debt						2,400
2017 Second Amendment Debt Facilities [Member]
Debt Instrument [Line Items]
Payments on debt						60,000
Deferred finance costs, gross						4,400
Payments of Debt Issuance Costs						6,900
2017 Second Amendment Debt Facilities Deemed Extinguishment of Debt [Member]
Debt Instrument [Line Items]
Payments of Debt Issuance Costs						1,300
2017 Second Amendment Debt Facilities Remaining [Member]
Debt Instrument [Line Items]
Payments of Debt Issuance Costs						2,500
2017 Second Amendment Debt Facilities Third Party Fees [Member]
Debt Instrument [Line Items]
Payments of Debt Issuance Costs						1,200
INSW Facilities [Member]
Debt Instrument [Line Items]
Interest Expense				35,895	64,982	58,878
2017 Term Loan, ABN Term Loan Facility and 10.75% Subordinated Notes [Member]
Debt Instrument [Line Items]
Write off of deferred debt issuance cost				12,500
2020 Debt Facilities [Member]
Debt Instrument [Line Items]
Deferred finance costs, gross				7,300
Core Revolving Facility [Member]
Debt Instrument [Line Items]
Interest Expense				660	$ 0	0
Core Term Loan Facility and Transition Term Loan Facility [Member]
Debt Instrument [Line Items]
Deferred finance costs, gross				6,500
Core Term Loan Facility And Transition Term Loan Facility Remaining Deferred Costs [Member]
Debt Instrument [Line Items]
Deferred finance costs, gross				6,300
Core Term Loan Facility and Transition Term Loan Facility Deemed Expensed [Member]
Debt Instrument [Line Items]
Deferred finance costs, gross				$ 200
10.75% Subordinated Notes [Member]
Debt Instrument [Line Items]
Debt instrument, repurchase amount							$ 27,900
Debt instrument, interest rate, stated percentage				10.75%	10.75%
8.5% Senior Notes [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage				8.50%	8.50%
Revolving Credit Facility [Member] | INSW Facilities [Member]
Debt Instrument [Line Items]
Deferred finance costs, gross					$ 300
Revolving Credit Facility [Member] | Core Revolving Facility [Member]
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity				$ 40,000			40,000
Long-term line of credit							$ 20,000
Deferred finance costs, gross				$ 800
Secured Debt [Member] | 2020 Debt Facilities [Member]
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity								$ 390,000
Term Loan [Member] | 2017 Debt Facilities [Member]
Debt Instrument [Line Items]
Payments on debt	$ (100,000)	$ 100,000	$ 10,000
Write off of deferred debt issuance cost					3,600
Gain (Loss) on extinguishment of debt					(4,700)
Debt instrument prepayment percentage				1.00%
Debt instrument prepayment fee amount					1,100
Term Loan [Member] | Core Term Loan Facility [Member]
Debt Instrument [Line Items]
Interest Expense				$ 13,542	0	0
Line of credit facility, maximum borrowing capacity				300,000
Term Loan [Member] | Core Revolving Facility [Member]
Debt Instrument [Line Items]
Deferred finance costs, gross				800
Term Loan [Member] | Transition Facility [Member]
Debt Instrument [Line Items]
Interest Expense				1,518	0	0
Line of credit facility, maximum borrowing capacity								$ 50,000
Write off of deferred debt issuance cost				600
Debt instrument prepayment fee amount				200
Senior Notes [Member] | 8.5% Senior Notes [Member]
Debt Instrument [Line Items]
Interest Expense				$ 2,417	$ 2,390	$ 1,396
Debt instrument, face amount										$ 25,000
Debt instrument, interest rate, stated percentage				8.50%	8.50%	8.50%			8.50%	8.50%
Subordinated Debt [Member] | 10.75% Subordinated Notes [Member]
Debt Instrument [Line Items]
Interest Expense				$ 276	$ 3,642	$ 2,032
Debt instrument, repurchase amount						$ 2,100
Debt instrument prepayment fee amount				$ 1,000
Debt instrument, interest rate, stated percentage				10.75%	10.75%	10.75%			10.75%

DEBT (Contractual Obligation, F

DEBT (Contractual Obligation, Fiscal Year Maturity Schedule Table 1) (Details) - INSW Facilities [Member] $ in Thousands	Dec. 31, 2020USD ($)
Schedule Of Long Term Debt Maturities Repayments Of Principal Line Items
2021	$ 61,483
2022	61,483
2023	86,484
2024	61,483
2025	143,532
Thereafter	128,233
Long-term Debt, Total	$ 542,698

FAIR VALUE OF FINANCIAL INSTR_3

FAIR VALUE OF FINANCIAL INSTRUMENTS, DERIVATIVES AND FAIR VALUE DISCLOSURES (Narrative) (Details) - USD ($) $ in Thousands

Apr. 16, 2020

Jan. 28, 2020

Oct. 08, 2019

Jul. 31, 2020

Oct. 31, 2019

Jul. 31, 2019

May 31, 2019

Apr. 30, 2019

Mar. 31, 2020

Dec. 31, 2019

Dec. 31, 2020

Dec. 31, 2019

Dec. 31, 2018

Jan. 27, 2020

Fair Value Of Financial Instruments Derivatives And Fair Value Disclosures [Line Items]

Derivative, notional amount

$ 25,000

Derivative, fixed interest rate

0.50%

Derivative, maturity date

Jan. 23, 2025

Debt instrument, interest rate, stated percentage

10.75%

Extinguishment of debt

$ 422,699

$ 110,000

$ 62,069

Change in fair value of interest rate collar recorded through earnings

$ (1,271)

923

Reclassification from AOCI to Earnings

500

Interest Rate Cap/Collar [Member]

Fair Value Of Financial Instruments Derivatives And Fair Value Disclosures [Line Items]

Derivative, notional amount

$ 250,000

$ 350,000

$ 350,000

$ 350,000

Derivative, cap interest rate

2.605%

2.605%

Derivative, fixed interest rate

1.97%

Derivative, maturity date

Jan. 23, 2025

Dec. 31, 2020

Average floor rate

0.00%

Change in fair value of interest rate collar recorded through earnings

$ (1,300)

$ 900

Current Period Through December 31 2020 [Member]

Fair Value Of Financial Instruments Derivatives And Fair Value Disclosures [Line Items]

Average cap rate

1.98%

Average floor rate

1.98%

December 31, 2020 Through December 31, 2022 [Member]

Fair Value Of Financial Instruments Derivatives And Fair Value Disclosures [Line Items]

Average cap rate

2.26%

Average floor rate

1.25%

Sinosure Credit Facility [Member]

Fair Value Of Financial Instruments Derivatives And Fair Value Disclosures [Line Items]

Derivative, fixed interest rate

2.35%

2.76%

2.99%

Derivative, maturity date

Dec. 21, 2027

Mar. 21, 2025

Mar. 21, 2022

2017 Debt Facilities [Member] | Term Loan [Member]

Fair Value Of Financial Instruments Derivatives And Fair Value Disclosures [Line Items]

Payments on debt

$ (100,000)

$ 100,000

$ 10,000

FAIR VALUE OF FINANCIAL INSTR_4

FAIR VALUE OF FINANCIAL INSTRUMENTS, DERIVATIVES AND FAIR VALUE DISCLOSURES (Other Than Derivatives) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Jun. 30, 2018	May 31, 2018
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Restricted cash	$ 16,287	$ 60,572
Debt instrument, interest rate, stated percentage	10.75%
Estimate of Fair Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	$ 215,677	150,243
Sinosure Credit Facility [Member] | Estimate of Fair Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans Payable, Fair Value Disclosure	$ (246,127)	$ (269,705)
8.5% Senior Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt instrument, interest rate, stated percentage	8.50%	8.50%
8.5% Senior Notes [Member] | Estimate of Fair Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes Payable, Fair Value Disclosure		$ (26,120)
10.75% Subordinated Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt instrument, interest rate, stated percentage	10.75%	10.75%
Term Loan [Member] | INSW Facilities [Member] | Estimate of Fair Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans Payable, Fair Value Disclosure	$ (271,571)	$ (333,177)
Term Loan [Member] | ABN Term Loan Facility [Member] | Estimate of Fair Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans Payable, Fair Value Disclosure		$ (23,248)
Senior Notes [Member] | 8.5% Senior Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt instrument, interest rate, stated percentage	8.50%	8.50%	8.50%	8.50%	8.50%
Debt instrument, maturity date	Jun. 30, 2023
Senior Notes [Member] | 8.5% Senior Notes [Member] | Estimate of Fair Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes Payable, Fair Value Disclosure	$ (25,697)
Subordinated Debt [Member] | 10.75% Subordinated Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt instrument, interest rate, stated percentage	10.75%	10.75%	10.75%	10.75%
Subordinated Debt [Member] | 10.75% Subordinated Notes [Member] | Estimate of Fair Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes Payable, Fair Value Disclosure		$ (32,649)
Fair Value, Inputs, Level 1 [Member] | Estimate of Fair Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	$ 215,677	150,243
Fair Value, Inputs, Level 1 [Member] | 8.5% Senior Notes [Member] | Estimate of Fair Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes Payable, Fair Value Disclosure		(26,120)
Fair Value, Inputs, Level 1 [Member] | Senior Notes [Member] | 8.5% Senior Notes [Member] | Estimate of Fair Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes Payable, Fair Value Disclosure	(25,697)
Fair Value, Inputs, Level 2 [Member] | Sinosure Credit Facility [Member] | Estimate of Fair Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans Payable, Fair Value Disclosure	(246,127)	(269,705)
Fair Value, Inputs, Level 2 [Member] | Term Loan [Member] | INSW Facilities [Member] | Estimate of Fair Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans Payable, Fair Value Disclosure	$ (271,571)	(333,177)
Fair Value, Inputs, Level 2 [Member] | Term Loan [Member] | ABN Term Loan Facility [Member] | Estimate of Fair Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans Payable, Fair Value Disclosure		(23,248)
Fair Value, Inputs, Level 2 [Member] | Subordinated Debt [Member] | 10.75% Subordinated Notes [Member] | Estimate of Fair Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes Payable, Fair Value Disclosure		$ (32,649)

FAIR VALUE OF FINANCIAL INSTR_5

FAIR VALUE OF FINANCIAL INSTRUMENTS, DERIVATIVES AND FAIR VALUE DISCLOSURES (Fair Value of Derivative Instruments) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Non Current Portion of Derivative Asset [Member]
Derivative Asset, Fair Value, Gross Asset Including Not Subject to Master Netting Arrangement	$ 2,129	$ 0
Current Portion of Derivative Liability [Member]
Derivative Instruments in Hedges, Liabilities, at Fair Value	(4,121)	(3,614)
Non Current Portion of Derivative Liability [Member]
Derivative Instruments in Hedges, Liabilities, at Fair Value	(6,155)	(6,545)
Accounts Payable, Accrued Liabilities And Other Current Liabilities [Member]
Derivative Instruments in Hedges, Liabilities, at Fair Value	(2,979)	0
Other Liabilities [Member]
Derivative Instruments in Hedges, Liabilities, at Fair Value	(14,051)	0
Interest Rate Swap [Member] | Non Current Portion of Derivative Asset [Member] | Hybrid Instrument [Member]
Derivative Asset, Fair Value, Gross Asset Including Not Subject to Master Netting Arrangement	0
Interest Rate Swap [Member] | Current Portion of Derivative Liability [Member] | Hybrid Instrument [Member]
Derivative Instruments in Hedges, Liabilities, at Fair Value	0
Interest Rate Swap [Member] | Non Current Portion of Derivative Liability [Member] | Hybrid Instrument [Member]
Derivative Instruments in Hedges, Liabilities, at Fair Value	0
Interest Rate Swap [Member] | Accounts Payable, Accrued Liabilities And Other Current Liabilities [Member] | Hybrid Instrument [Member]
Derivative Instruments in Hedges, Liabilities, at Fair Value	(2,979)
Interest Rate Swap [Member] | Other Liabilities [Member] | Hybrid Instrument [Member]
Derivative Instruments in Hedges, Liabilities, at Fair Value	(14,051)
Not Designated as Hedging Instrument [Member] | Interest Rate Cap/Collar [Member] | Non Current Portion of Derivative Asset [Member]
Derivative Asset, Fair Value, Gross Asset Including Not Subject to Master Netting Arrangement		0
Not Designated as Hedging Instrument [Member] | Interest Rate Cap/Collar [Member] | Current Portion of Derivative Liability [Member]
Derivative Instruments in Hedges, Liabilities, at Fair Value		(1,230)
Not Designated as Hedging Instrument [Member] | Interest Rate Cap/Collar [Member] | Non Current Portion of Derivative Liability [Member]
Derivative Instruments in Hedges, Liabilities, at Fair Value		(577)
Not Designated as Hedging Instrument [Member] | Interest Rate Cap/Collar [Member] | Accounts Payable, Accrued Liabilities And Other Current Liabilities [Member]
Derivative Instruments in Hedges, Liabilities, at Fair Value		0
Not Designated as Hedging Instrument [Member] | Interest Rate Cap/Collar [Member] | Other Liabilities [Member]
Derivative Instruments in Hedges, Liabilities, at Fair Value		0
Cash Flow Hedging [Member] | Designated as Hedging Instrument [Member] | Interest Rate Swap [Member] | Non Current Portion of Derivative Asset [Member]
Derivative Asset, Fair Value, Gross Asset Including Not Subject to Master Netting Arrangement	2,129	0
Cash Flow Hedging [Member] | Designated as Hedging Instrument [Member] | Interest Rate Swap [Member] | Current Portion of Derivative Liability [Member]
Derivative Instruments in Hedges, Liabilities, at Fair Value	(4,121)	(2,384)
Cash Flow Hedging [Member] | Designated as Hedging Instrument [Member] | Interest Rate Swap [Member] | Non Current Portion of Derivative Liability [Member]
Derivative Instruments in Hedges, Liabilities, at Fair Value	(6,155)	(5,968)
Cash Flow Hedging [Member] | Designated as Hedging Instrument [Member] | Interest Rate Swap [Member] | Accounts Payable, Accrued Liabilities And Other Current Liabilities [Member]
Derivative Instruments in Hedges, Liabilities, at Fair Value	0	0
Cash Flow Hedging [Member] | Designated as Hedging Instrument [Member] | Interest Rate Swap [Member] | Other Liabilities [Member]
Derivative Instruments in Hedges, Liabilities, at Fair Value	$ 0	$ 0

FAIR VALUE OF FINANCIAL INSTR_6

FAIR VALUE OF FINANCIAL INSTRUMENTS, DERIVATIVES AND FAIR VALUE DISCLOSURES (Effect of Cash Flow Hedging Relationships) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Cash Flow Hedging [Member]
Total other comprehensive loss	$ (21,503)	$ (19,126)	$ (1,687)
Designated as Hedging Instrument [Member] | Cash Flow Hedging [Member] | Interest Rate Cap/Collar [Member]
Total other comprehensive loss	0	(3,905)	261
Designated as Hedging Instrument [Member] | Cash Flow Hedging [Member] | Interest Rate Swap [Member]
Total other comprehensive loss	(20,123)	(15,221)	(1,948)
Hybrid Instrument [Member] | Interest Rate Swap [Member]
Total other comprehensive loss	$ (1,380)	$ 0	$ 0

FAIR VALUE OF FINANCIAL INSTR_7

FAIR VALUE OF FINANCIAL INSTRUMENTS, DERIVATIVES AND FAIR VALUE DISCLOSURES (Effect of Cash Flow Hedging Relationships on Consolidated Statements of Operations) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Effective portion of gain/(loss) reclassified from accumulated other comprehensive loss	$ (9,521)	$ (29,303)	$ (11,058)
Cash Flow Hedging [Member] | Interest Expense [Member]
Effective portion of gain/(loss) reclassified from accumulated other comprehensive loss	9,299	1,501	492
Cash Flow Hedging [Member] | Designated as Hedging Instrument [Member] | Interest Rate Cap/Collar [Member]
Effective portion of gain/(loss) reclassified from accumulated other comprehensive loss	0	99	21
Cash Flow Hedging [Member] | Designated as Hedging Instrument [Member] | Interest Rate Swap [Member]
Effective portion of gain/(loss) reclassified from accumulated other comprehensive loss	4,571	1,467	471
Cash Flow Hedging [Member] | Not Designated as Hedging Instrument [Member] | Interest Rate Cap/Collar [Member]
Effective portion of gain/(loss) reclassified from accumulated other comprehensive loss	1,352	(65)	0
Hybrid Instrument [Member] | Interest Rate Swap [Member]
Effective portion of gain/(loss) reclassified from accumulated other comprehensive loss	$ 3,376	$ 0	$ 0

FAIR VALUE OF FINANCIAL INSTR_8

FAIR VALUE OF FINANCIAL INSTRUMENTS, DERIVATIVES AND FAIR VALUE DISCLOSURES (Fair Values of Assets and Liabilities Measured on Recurring Basis) (Details) - Fair Value, Measurements, Recurring [Member] - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Interest Rate Swaps and Collar [Member]
Derivative Asset		$ 0
Derivative liability		(10,159)
Interest Rate Swaps and Collar [Member] | Fair Value, Inputs, Level 2 [Member]
Derivative Asset		0
Derivative liability		$ (10,159)
Interest Rate Swap [Member]
Derivative Asset	$ 2,129
Derivative liability	(10,276)
Interest Rate Swap [Member] | Fair Value, Inputs, Level 2 [Member]
Derivative Asset	2,129
Derivative liability	$ (10,276)

FAIR VALUE OF FINANCIAL INSTR_9

FAIR VALUE OF FINANCIAL INSTRUMENTS, DERIVATIVES AND FAIR VALUE DISCLOSURES (Fair Value of Items Measured on Nonrecurring Basis) (Details)	1 Months Ended		3 Months Ended				12 Months Ended
	Oct. 31, 2020USD ($)	Oct. 31, 2020property	Dec. 31, 2020USD ($)property	Sep. 30, 2020USD ($)property	Jun. 30, 2020USD ($)property	Sep. 30, 2018USD ($)property	Dec. 31, 2020USD ($)property	Dec. 31, 2018USD ($)property
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impairment						$ (16,400,000)
Number of vessels marketed to be sold | property			2
Number of vessels with impairment triggering events | property								3
International Crude Tankers Segment [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Property, plant and equipment, fair value			$ 134,035,000				$ 134,035,000
Vessels held for use, Impairment Charges							(47,265,000)
International Crude Tankers Segment [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Property, plant and equipment, fair value			134,035,000				134,035,000
International Product Carriers Segment [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Property, plant and equipment, fair value			113,250,000				113,250,000
Vessels held for use, Impairment Charges							(55,757,000)
International Product Carriers Segment [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Property, plant and equipment, fair value			113,250,000				113,250,000
Vessel/Fleet [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impairment							(341,065,000)	$ (58,021,000)
4 MRs Vessels
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Property, plant and equipment, fair value			113,300,000				$ 113,300,000
2 LR1s and 4 MRs | International Product Carriers Segment [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Vessels held for use, Impairment Charges			$ 55,700,000
Very Large Crude Carrier [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impairment						$ (14,200,000)
Number of vessels with impairment triggering events | property			1			1	1
2 VLCCs to be sold [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Number of vessels marketed to be sold	2	2					2
Number of vessels with impairment triggering events | property			2				2
1 of 2 VLCCs to be sold [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impairment					$ (5,500,000)
Very Large Crude Carrier Cost To Sell [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impairment						$ (400,000)
Very Large Crude Carrier Operational Costs [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impairment						$ (1,800,000)
One VLCC
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Property, plant and equipment, fair value			$ 53,100,000		$ 30,400,000		$ 53,100,000
Number of vessels with impairment triggering events | property			1		1		1
One VLCC | International Crude Tankers Segment [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Vessels held for use, Impairment Charges			$ (30,100,000)		$ (5,500,000)
Number of vessels with impairment triggering events | property			1		1		1
2 VLCCs
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Property, plant and equipment, fair value				$ 50,500,000
Number of vessels with impairment triggering events | property				2
2 VLCCs | International Crude Tankers Segment [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Vessels held for use, Impairment Charges				$ (11,700,000)
Number of vessels with impairment triggering events | property					2
LR1 Vessel [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Number of vessels with impairment triggering events | property			2				2
LR1 Vessel [Member] | International Product Carriers Segment [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Number of vessels with impairment triggering events | property			2				2
MR Vessel [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Number of vessels with impairment triggering events | property			4				4
MR Vessel [Member] | International Product Carriers Segment [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Number of vessels with impairment triggering events | property			4				4
Aframaxes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Number of vessels with impairment triggering events | property			1				1
Aframaxes [Member] | International Crude Tankers Segment [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Number of vessels with impairment triggering events | property			1				1

ACCOUNTS PAYABLE, ACCRUED EXP_3

ACCOUNTS PAYABLE, ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES (Schedule of Accounts Payable, Accrued Expenses and Other Current Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
ACCOUNTS PAYABLE, ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES [Abstract]
Accounts payable	$ 2,609	$ 4,988
Payroll and benefits	6,293	5,585
Interest	370	594
Other-than-insignificant financing element of derivatives	2,979	0
Due to owners on chartered in vessels	787	1,108
Accrued drydock, repairs and vessel betterment costs	6,247	3,150
Bunkers and lubricants	656	538
Charter revenues received in advance	3,060	272
Insurance	493	539
Accrued vessel expenses	8,779	8,003
Accrued general and administrative expenses	940	1,052
Other	1,212	1,725
Total accounts payable, accrued expense and other current liabilities	$ 34,425	$ 27,554

TAXES (Narrative) (Details)

TAXES (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
TAXES [Abstract]
Percent of shipping income subject to U.S. federal taxation	4.00%
Operating loss carryforwards	$ 11,400	$ 10,800
Indefinite-lived net operating loss carryforwards	11,400
Operating loss carryforwards, valuation allowance	4,700	4,200
Increase (decrease) in valuation allowance	500
Unrecognized tax benefits, interest on income taxes accrued	7	5
Unrecognized tax benefits	$ 7	$ 7

TAXES (Components of Income Tax

TAXES (Components of Income Tax (Provisions) and Benefits) (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
TAXES [Abstract]
Current		$ (1)	$ (1)	$ 105
Deferred		0	0	0
Income tax (provision)/benefit	$ (1)	$ (1)	$ (1)	$ 105

TAXES (Reconciliation of Effect

TAXES (Reconciliation of Effective to Statutory Tax Rate) (Details) - MARSHALL ISLANDS [Member] - Foreign Tax Authority [Member]	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Adjustments due to:
Change in valuation allowance	0.66%	0.66%	(0.66%)
Income subject to tax in other jurisdictions	(0.65%)	(0.83%)	0.54%
Effective tax rate	0.01%	(0.17%)	(0.12%)

TAXES (Components of Deferred T

TAXES (Components of Deferred Tax Liabilities and Assets) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Deferred tax assets:
Net operating loss carryforwards	$ 2,173	$ 1,836
Excess of tax over book basis of depreciable assets	612	548
Pensions	1,950	1,797
Total deferred tax assets	4,735	4,181
Less: Valuation allowance	(4,735)	(4,181)
Net deferred tax assets
Net noncurrent deferred tax assets

CAPITAL STOCK AND STOCK COMPE_3

CAPITAL STOCK AND STOCK COMPENSATION (Narrative) (Details) - USD ($) $ / shares in Units, $ in Thousands

Feb. 23, 2021

Dec. 23, 2020

Oct. 28, 2020

Sep. 23, 2020

Aug. 04, 2020

Jul. 08, 2020

Jun. 22, 2020

May 20, 2020

Mar. 30, 2020

Feb. 26, 2020

Jul. 31, 2020

Dec. 31, 2019

Jul. 31, 2019

Apr. 30, 2019

Apr. 30, 2018

Dec. 31, 2020

Jun. 30, 2020

Dec. 31, 2020

Dec. 31, 2019

Dec. 31, 2018

Mar. 05, 2019

Nov. 18, 2016

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Restricted stock or unit expense

$ 4,600

$ 3,200

$ 2,300

Share-based compensation arrangement by share-based payment award, options, outstanding, weighted average remaining contractual term

7 years 1 month 24 days

Share-based compensation arrangement by share-based payment award, options, exercisable, weighted average remaining contractual term

6 years 2 months 12 days

Stock options, compensation expense (income)

$ 1,100

$ 1,100

$ 900

Share based compensation expense, unrecognized

$ 4,800

$ 4,800

Share based compensation expense, unrecognized, period

1 year 7 months 24 days

Share-based Compensation Arrangement by Share-based Payment Award, Shares Purchased for Award

75,894

21,589

28,002

Share-based Compensation Arrangement by Share-based Payment Award, Per Share Weighted Average Price of Shares Purchased

$ 17.07

$ 20.31

$ 20.31

$ 17.07

$ 17.81

Stock Repurchased and Retired During Period, Shares

0

1,417,292

0

0

Stock Repurchased and Retired During Period, Value

$ 30,000

Treasury Stock Acquired, Average Cost Per Share

$ 21.16

Stock repurchase program, authorized amount

$ 50,000

$ 30,000

$ 30,000

Stock repurchase program, period in force

24 months

24 months

Stock Repurchase Program Expiration Date

Aug. 4, 2022

Mar. 5, 2021

Compensation expense, deferred

$ 100

Dividends payable, date declared

Oct. 28, 2020

Aug. 4, 2020

May 20, 2020

Feb. 26, 2020

Dividends payable, amount per share

$ 0.06

$ 0.06

$ 0.06

$ 0.06

Dividends payable, date of record

Dec. 8, 2020

Sep. 9, 2020

Jun. 8, 2020

Mar. 17, 2020

Payments of dividends

$ 1,700

$ 1,700

$ 1,700

$ 1,700

$ 6,770

Subsequent Event [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Dividends payable, date declared

Feb. 23, 2021

Dividends payable, amount per share

$ 0.06

Dividends payable, date of record

Mar. 11, 2021

Certain Employees and Senior Officers [Member] | 2019 Award [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Grant date, value, per share

21.93

Senior Officers [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Share based arrangement exercisable option period, maximum

90 days

Restricted Stock [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Other than options, vested

6,230

Other than options, vested fair value

$ 100

Time Based Restricted Stock [Member] | Certain Employees and Senior Officers [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Granted

44,466

26,451

Granted, per share

$ 27.66

$ 19

Performance Shares [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Granted

58,258

63,994

55,534

Granted, per share

$ 17.83

$ 17.21

$ 17.46

Grant date, value, per share

17.59

16.68

18.87

Share based arrangement fair value method used

Monte Carlo probability model

Performance Shares [Member] | Executive Officer [Member] | February 14, 2017 [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Share-based Compensation Arrangement by Share-based Payment Award, Performance Payout Percentage

72.00%

Share based award payout percentage of target achieved

126.00%

Performance Shares [Member] | Executive Officer [Member] | Share-based Payment Arrangement, Tranche Two [Member] | February 14, 2017 [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Granted

11,882

Granted, per share

$ 17.46

Performance Shares [Member] | Executive Officer [Member] | Share-based Payment Arrangement, Tranche Three [Member] | February 14, 2017 [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Granted

11,882

Grant date, value, per share

17.21

Performance Shares Based on Total Shareholder Return (TSR) [Member] | 2018 Awarded [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Share-based Compensation Arrangement by Share-based Payment Award, Performance Payout Percentage

100.00%

Performance Shares Based On Return On Invested Capital [Member] | 2018 Awarded [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Share-based Compensation Arrangement by Share-based Payment Award, Performance Payout Percentage

130.00%

Employee Stock Option [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Granted, options

131,992

137,847

124,955

Employee Stock Option [Member] | Certain Employees and Senior Officers [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Granted, options

131,992

137,847

124,955

Grants, options, per share

$ 9.68

$ 7.99

$ 7.76

Employee Stock Option [Member] | Certain Employees and Senior Officers [Member] | 2018 Awarded [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Grant date, value, per share

17.21

Employee Stock Option [Member] | Certain Employees and Senior Officers [Member] | 2017 Award [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Grant date, value, per share

17.46

Spin Off Options [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Fair value assumptions, risk free interest rate

0.44%

2.36%

Spin Off Options Outstanding [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Share-based compensation, shares authorized under stock option plans, exercise price range, outstanding options, weighted average exercise price

$ 19.78

$ 19.78

Spin Off Options Exercisable [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Share-based compensation, shares authorized under stock option plans, exercise price range, outstanding options, weighted average exercise price

$ 19.90

$ 19.90

Management Incentive Compensation Plan [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Shares authorized, share plans

2,000,000

Shares authorized, share plans, additional

1,400,000

Management Incentive Compensation Plan [Member] | Time Based Restricted Stock [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Granted

58,258

63,998

55,536

Granted, per share

$ 21.93

$ 17.21

$ 17.46

Management Incentive Compensation Plan [Member] | Spin Off Options [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Share based arrangement fair value method used

Black-Scholes option pricing model

Fair value assumptions, expected dividend rate

1.02%

0.00%

0.00%

Fair value assumptions, expected volatility factor

0.52%

0.46%

0.42%

Fair value assumptions, expected life

6 years

6 years

6 years

Management Incentive Compensation Plan [Member] | Spin Off Options [Member] | Maximum [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Fair value assumptions, risk free interest rate

2.67%

Management Incentive Compensation Plan [Member] | Spin Off Options Outstanding [Member] | Exercise Prices Ranging from $17.21 to $30.93 [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Lower range, price

$ 17.21

Upper range, price

$ 30.93

Non-Employee Director Incentive Compensation Plan [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Shares authorized, share plans

400,000

Shares authorized, share plans, additional

400,000

Non-Employee Director Incentive Compensation Plan [Member] | Restricted Stock [Member] | Directors [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Granted

57,317

51,107

47,501

Granted, per share

$ 16.05

$ 18

$ 18.82

CAPITAL STOCK AND STOCK COMPE_4

CAPITAL STOCK AND STOCK COMPENSATION (Restricted Stock Activity) (Details) - $ / shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Restricted Common Stock and Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Nonvested Shares Outstanding Beginning Balance	305,883	352,864	230,201	174,177
Granted	182,142	270,096	173,573
Forfeited		(20,570)	(19,995)
Vested	(229,123)	(126,863)	(97,554)
Nonvested Shares Outstanding Ending Balance	305,883	352,864	230,201
Lower range, price	$ 17.21	$ 17.46	$ 18.62
Upper range, price	$ 27.66	$ 29.61	$ 24.05
Shares paid for tax withholding for share based compensation	71,513	21,529	21,752
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted	58,258	63,994	55,534
Performance Shares Achieved [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted	8,309	8,198	3,120

CAPITAL STOCK AND STOCK COMPE_5

CAPITAL STOCK AND STOCK COMPENSATION (Stock Option Activity) (Details) - Employee Stock Option [Member] - shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options Outstanding Beginning Balance	538,632	400,785	275,830
Granted	131,992	137,847	124,955
Exercised
Options Outstanding Ending Balance	670,624	538,632	400,785
Options Exercisable	405,082

ACCUMULATED OTHER COMPREHENSI_3

ACCUMULATED OTHER COMPREHENSIVE LOSS (Narrative) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2020USD ($)
ACCUMULATED OTHER COMPREHENSIVE LOSS [Abstract]
Unrecognized prior service credits	$ 1.4
Unrecognized prior service credits, net of tax	1
Unrecognized actuarial losses	8.9
Unrecognized actuarial losses, net of tax	7.5
Derivative instruments, gain (loss) reclassification from accumulated oci to income, estimated net amount to be transferred	$ 9.6

ACCUMULATED OTHER COMPREHENSI_4

ACCUMULATED OTHER COMPREHENSIVE LOSS (Components of Accumulated Other Comprehensive Loss) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
ACCUMULATED OTHER COMPREHENSIVE LOSS [Abstract]
Unrealized losses on derivative instruments	$ (24,098)	$ (11,732)
Items not yet recognized as a component of net periodic benefit cost (pension plans)	(8,515)	(8,838)
Accumulated other comprehensive loss	$ (32,613)	$ (20,570)

ACCUMULATED OTHER COMPREHENSI_5

ACCUMULATED OTHER COMPREHENSIVE LOSS (Changes in Components of AOCI, Net of Related Taxes) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Balance, beginning	$ 1,022,293	$ 1,009,855	$ 1,085,654
Other Comprehensive (Loss)/Income, net of tax	(12,043)	9,359	10,478
Balance, ending	972,042	1,022,293	1,009,855
Accumulated Other Comprehensive Loss [Member]
Balance, beginning	(20,570)	(29,929)	(40,407)
Current period change, excluding amounts reclassified from accumulated other comprehensive loss	(21,564)	(19,944)	(580)
Amounts reclassified from accumulated other comprehensive loss	9,521	29,303	11,058
Other Comprehensive (Loss)/Income, net of tax	(12,043)	9,359	10,478
Balance, ending	(32,613)	(20,570)	(29,929)
Unrealized losses on cash flow hedges [Member]
Balance, beginning	(11,732)	(21,520)	(28,989)
Current period change, excluding amounts reclassified from accumulated other comprehensive loss	(21,503)	(19,126)	(1,687)
Amounts reclassified from accumulated other comprehensive loss	9,137	28,914	9,156
Balance, ending	(24,098)	(11,732)	(21,520)
Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
Balance, beginning	(8,838)	(8,409)	(11,418)
Current period change, excluding amounts reclassified from accumulated other comprehensive loss	(61)	(818)	1,107
Amounts reclassified from accumulated other comprehensive loss	384	389	1,902
Balance, ending	$ (8,515)	$ (8,838)	$ (8,409)

ACCUMULATED OTHER COMPREHENSI_6

ACCUMULATED OTHER COMPREHENSIVE LOSS (Amounts Reclassified out of AOCI) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Unrealized losses on available-for-sale securities:
Equity in income of affiliated companies									$ (5,530)	$ (829)	$ (89,045)
Income (loss) from equity method investments	$ (11,553)	$ 5,356	$ 5,205	$ 5,111	$ (13,346)	$ 8,474	$ 8,015	$ 8,070	4,119	11,213	29,432
Interest expense	$ 7,823	$ 7,999	$ 8,881	$ 12,009	$ 14,281	$ 17,010	$ 17,443	$ 17,533	36,712	66,267	60,231
Other income/(expense)									(12,817)	(943)	(3,715)
Total reclassified out of AOCL, before tax									(9,521)	(29,303)	(11,058)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Unrealized losses on cash flow hedges [Member]
Unrealized losses on available-for-sale securities:
Other income/(expense)									384	389	1,902
Interest Rate Swap [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Unrealized losses on cash flow hedges [Member]
Unrealized losses on available-for-sale securities:
Income (loss) from equity method investments									(1,109)	(26,490)	(8,664)
Interest expense									4,571	1,467	471
Interest Rate Cap/Collar [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Unrealized losses on available-for-sale securities:
Interest expense									81	858	0
Interest Rate Cap/Collar [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Unrealized losses on cash flow hedges [Member]
Unrealized losses on available-for-sale securities:
Interest expense									0	99	21
Hybrid Instrument [Member] | Interest Rate Swap [Member]
Unrealized losses on available-for-sale securities:
Total reclassified out of AOCL, before tax									3,376	0	0
Hybrid Instrument [Member] | Interest Rate Swap [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Unrealized losses on available-for-sale securities:
Interest expense									$ 3,376	$ 0	$ 0

REVENUE (Narrative) (Details)

REVENUE (Narrative) (Details) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020USD ($)	Sep. 30, 2020USD ($)	Jun. 30, 2020USD ($)	Mar. 31, 2020USD ($)	Dec. 31, 2019USD ($)	Sep. 30, 2019USD ($)	Jun. 30, 2019USD ($)	Mar. 31, 2019USD ($)	Dec. 31, 2020USD ($)property	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)
Revenues, Total	$ 56,703	$ 99,883	$ 139,725	$ 125,337	$ 124,022	$ 71,278	$ 69,010	$ 101,874	$ 421,648	$ 366,184	$ 270,361
Contract with customer, performance obligation satisfied in previous period									47
Capitalized contract cost, gross	$ 0								$ 0
Term of profit sharing arrangement									1 year
Profit Loss To Be Shared, Percentage									25
Lease cancellation period notice									90 days
Contract with customer adjustment to estimates of performance obligations decrease										$ (493)
Very Large Crude Carrier [Member]
Number of vessels party to contracts | property									2
LR2 Vessel [Member]
Number of vessels party to contracts | property									1

REVENUE (Schedule of Disaggrega

REVENUE (Schedule of Disaggregated Revenue) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Revenue, non lease									$ 421,648	$ 366,184	$ 270,361
Shipping revenues	$ 56,703	$ 99,883	$ 139,725	$ 125,337	$ 124,022	$ 71,278	$ 69,010	$ 101,874	421,648	366,184	270,361
International Crude Tankers Segment [Member]
Revenue, non lease									334,765	285,356	202,396
Shipping revenues									334,765	285,356	202,396
International Product Carriers Segment [Member]
Revenue, non lease									86,883	80,828	67,965
Shipping revenues									86,883	80,828	67,965
Other Segment [Member]
Shipping revenues									0	0	0
Pool Revenue Leases [Member]
Shipping revenues									272,980	254,055	177,206
Pool Revenue Leases [Member] | Fixed-Price Contract [Member]
Revenue, operating leases									272,980	254,055	177,206
Pool Revenue Leases [Member] | International Crude Tankers Segment [Member] | Fixed-Price Contract [Member]
Revenue, operating leases									198,316	173,751	111,214
Pool Revenue Leases [Member] | International Product Carriers Segment [Member] | Fixed-Price Contract [Member]
Revenue, operating leases									74,664	80,304	65,992
Pool Revenue Leases [Member] | Other Segment [Member] | Fixed-Price Contract [Member]
Revenue, operating leases									0	0	0
Voyage Charter Leases Non Variable Payments [Member] | Fixed-Price Contract [Member]
Revenue, lease non-variable									29,472	30,220	20,782
Voyage Charter Leases Non Variable Payments [Member] | International Crude Tankers Segment [Member] | Fixed-Price Contract [Member]
Revenue, lease non-variable									19,016	29,786	20,682
Loss of hire proceeds									4,400		2,300
Voyage Charter Leases Non Variable Payments [Member] | International Product Carriers Segment [Member] | Fixed-Price Contract [Member]
Revenue, lease non-variable									10,456	434	100
Loss of hire proceeds										300
Voyage Charter Leases Non Variable Payments [Member] | Other Segment [Member] | Fixed-Price Contract [Member]
Revenue, lease non-variable									0	0	0
Voyage Charter Leases Variable Payments [Member] | Fixed-Price Contract [Member]
Revenue, operating leases									2,007	2,574	1,346
Voyage Charter Leases Variable Payments [Member] | International Crude Tankers Segment [Member] | Fixed-Price Contract [Member]
Revenue, operating leases									1,180	2,574	1,346
Voyage Charter Leases Variable Payments [Member] | International Product Carriers Segment [Member] | Fixed-Price Contract [Member]
Revenue, operating leases									827	0	0
Voyage Charter Leases Variable Payments [Member] | Other Segment [Member] | Fixed-Price Contract [Member]
Revenue, operating leases									0	0	0
Time and Bareboat Charter Leases [Member]
Shipping revenues									88,719	27,625	25,961
Time and Bareboat Charter Leases [Member] | Fixed-Price Contract [Member]
Revenue, operating leases									88,719	27,625	25,961
Time and Bareboat Charter Leases [Member] | International Crude Tankers Segment [Member] | Fixed-Price Contract [Member]
Revenue, operating leases									87,783	27,535	24,088
Time and Bareboat Charter Leases [Member] | International Product Carriers Segment [Member] | Fixed-Price Contract [Member]
Revenue, operating leases									936	90	1,873
Time and Bareboat Charter Leases [Member] | Other Segment [Member] | Fixed-Price Contract [Member]
Revenue, operating leases									0	0	0
Voyage Charter Leases [Member]
Revenue, non lease									472
Shipping revenues									59,949	84,504	67,194
Voyage Charter Leases [Member] | Time-and-materials Contract [Member]
Revenue, non lease											45,066
Voyage Charter Leases [Member] | Lightering Services Component [Member]
Revenue, non lease									27,998	51,710
Voyage Charter Leases [Member] | International Crude Tankers Segment [Member]
Revenue, non lease									472
Voyage Charter Leases [Member] | International Crude Tankers Segment [Member] | Time-and-materials Contract [Member]
Revenue, non lease											45,066
Voyage Charter Leases [Member] | International Crude Tankers Segment [Member] | Lightering Services Component [Member]
Revenue, non lease									27,998	51,710
Voyage Charter Leases [Member] | International Product Carriers Segment [Member]
Revenue, non lease									0
Voyage Charter Leases [Member] | International Product Carriers Segment [Member] | Time-and-materials Contract [Member]
Revenue, non lease											0
Voyage Charter Leases [Member] | International Product Carriers Segment [Member] | Lightering Services Component [Member]
Revenue, non lease									0	0
Voyage Charter Leases [Member] | Other Segment [Member]
Revenue, non lease									0
Voyage Charter Leases [Member] | Other Segment [Member] | Time-and-materials Contract [Member]
Revenue, non lease											$ 0
Voyage Charter Leases [Member] | Other Segment [Member] | Lightering Services Component [Member]
Revenue, non lease									$ 0	$ 0

REVENUE (Schedule of Contract R

REVENUE (Schedule of Contract Related Receivables, Assets and Liabilities with Customers) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Jan. 01, 2020
REVENUE [Abstract]
Voyage receivables - receivables	$ 2,148	$ 2,727
Contract asset (voyage receivables unbilled receivables)	$ 166

LEASES (Narrative) (Details)

LEASES (Narrative) (Details) - property	1 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2020
Leases [Line Items]
Lessee operating lease cancellation period notice		180 days
Excluded vessels chartered period		1 month
Number of vessels seized in dispute	2
Aframaxes [Member]
Leases [Line Items]
Number of vessels chartered		2
LR1 Vessel [Member]
Leases [Line Items]
Number of vessels chartered		1
Workboat Vessel [Member]
Leases [Line Items]
Number of vessels chartered		1
Bareboat Charters-In [Member] | Aframaxes [Member]
Leases [Line Items]
Number of vessels chartered		2

LEASES (Schedule of lease cost)

LEASES (Schedule of lease cost) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Operating lease, cost	$ 30,114	$ 57,512	$ 44,910
Total lease cost	17,492	27,198
Vessel/Fleet [Member] | Charter Hire Expense [Member]
Operating lease, cost	11,666	15,089
Short-term lease, cost	4,585	10,769
Office Space [Member] | General and Administrative Expense [Member]
Operating lease, cost	1,044	996
Short-term lease, cost	29	116
Office Space [Member] | Voyage Expense [Member]
Operating lease, cost	168	168
Short-term lease, cost		52
Office Space [Member] | Vessel Expense [Member]
Short-term lease, cost		8
Lightering Services Component [Member] | Vessel/Fleet [Member]
Short-term lease, cost	$ 1,200	$ 10,600

LEASES (Supplemental lease info

LEASES (Supplemental lease information) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Cash paid for amounts included in the measurement of lease liabilities
Operating cash flows used for operating leases	$ 12,878	$ 16,178
Operating Lease, Liability, Current	$ 8,867	12,958
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]	Operating Lease, Liability, Current
Operating Lease, Liability, Noncurrent	$ 10,253	17,953
Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	Operating Lease, Liability, Noncurrent
Operating Lease, Liability, Statement of Financial Position [Extensible List]	Total operating lease liabilities
Total operating lease liabilities	$ (19,120)	(30,911)
Operating Lease, Right-of-Use Asset	$ 21,588	$ 33,718
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	Operating Lease, Right-of-Use Asset
Operating Lease, Weighted Average Remaining Lease Term	2 years 9 months	3 years 2 months 26 days
Operating Lease, Weighted Average Discount Rate, Percent	7.21%	7.16%

LEASES (Bareboat and Time Chart

LEASES (Bareboat and Time Charters-In) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Leases [Line Items]
Total operating lease liabilities	$ 19,120	$ 30,911
Bareboat Charters-In [Member]
Leases [Line Items]
2021	6,278
2022	6,278
2023	4,532
Total lease payments	17,088
less imputed interest	(1,608)
Total operating lease liabilities	$ 15,480
2021, operating days	730 days
2022, operating days	730 days
2023, operating days	556 days
Operating days, total	2016 days
Time Charters-In [Member]
Leases [Line Items]
2021	$ 2,170
Total lease payments	2,170
less imputed interest	(43)
Total operating lease liabilities	$ 2,127
2021, operating days	408 days
Operating days, total	408 days

LEASES (Future Minimum Lease Ob

LEASES (Future Minimum Lease Obligations for Office Space) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Leases [Line Items]
Total operating lease liabilities	$ 19,120	$ 30,911
Office Space And Lightering Workboat Dock Space [Member]
Leases [Line Items]
2021	936
2022	273
2023	229
2024	178
Total lease payments	1,616
less imputed interest	(103)
Total operating lease liabilities	$ 1,513

LEASES (Future Minimum Revenues

LEASES (Future Minimum Revenues on Charters-Out) (Details) - Charters-Out [Member] $ in Thousands	12 Months Ended
	Dec. 31, 2020USD ($)
Operating Leases, Future Minimum Payments Receivable [Abstract]
2021	$ 28,856
2022	16,425
2023	3,195
Net minimum lease payments	$ 48,476
2021, revenue days	1053 days
2022, revenue days	365 days
2023, revenue days	71 days
Revenue Days	1489 days

PENSION AND OTHER POSTRETIREM_3

PENSION AND OTHER POSTRETIREMENT BENEFIT PLANS (Narrative) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, target plan asset allocations	100.00%
Defined benefit plan unrecognized actuarial losses amortization period	19 years
Defined contribution plan, employer discretionary contribution amount	$ 400,000	$ 400,000	$ 400,000
Equity Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, target plan asset allocations	80.00%
Fixed Income Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, target plan asset allocations	20.00%
Foreign Plan [Member] | Scheme Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, contributions by employer	$ 664,000	$ 639,000	$ 0

PENSION AND OTHER POSTRETIREM_4

PENSION AND OTHER POSTRETIREMENT BENEFIT PLANS (Schedule of Benefit Obligations in Excess of Fair Value of Plan Assets) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Change in benefit obligation:
Interest cost on benefit obligation	$ 525,000	$ 657,000	$ 707,000
Change in plan assets:
Fair value of plan assets at year end	31,219,000
Foreign Plan [Member] | Scheme Plan [Member]
Change in benefit obligation:
Benefit obligation at beginning of year	27,481,000	23,814,000
Interest cost on benefit obligation	525,000	657,000
Actuarial losses	2,202,000	2,761,000
Benefits paid	(875,000)	(820,000)
Foreign exchange losses/(gains)	943,000	1,069,000
Benefit obligation at year end	30,276,000	27,481,000	23,814,000
Change in plan assets:
Fair value of plan assets at beginning of year	26,994,000	22,785,000
Actual return on plan assets	3,427,000	3,341,000
Employer contributions	664,000	639,000	0
Benefits paid	(875,000)	(820,000)
Foreign exchange gains/(losses)	1,009,000	1,049,000
Fair value of plan assets at year end	31,219,000	26,994,000	$ 22,785,000
Funded/(unfunded) status at December 31	$ 943,000	$ (487,000)

PENSION AND OTHER POSTRETIREM_5

PENSION AND OTHER POSTRETIREMENT BENEFIT PLANS (Components of Expense, Domestic Plans) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Components of expense:
Defined benefit plan, interest cost	$ 525	$ 657	$ 707
Expected return on plan assets	(1,018)	(1,017)	(1,029)
Amortization of prior-service costs	75	74	71
Recognized net actuarial loss	310	315	388
Recognized settlement loss			1,442
Net periodic (benefit)/cost	$ (108)	$ 29	$ 1,579

PENSION AND OTHER POSTRETIREM_6

PENSION AND OTHER POSTRETIREMENT BENEFIT PLANS (Weighted-Average Assumptions Used to Determine Benefit Obligations) (Details)	Dec. 31, 2020	Dec. 31, 2019
Pension and Other Postretirement Benefit Plans [Abstract]
Discount rate	1.20%	2.00%

PENSION AND OTHER POSTRETIREM_7

PENSION AND OTHER POSTRETIREMENT BENEFIT PLANS (Assumptions Used to Determine Net Periodic Benefit Cost) (Details)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Pension and Other Postretirement Benefit Plans [Abstract]
Discount rate	2.00%	2.80%	2.40%
Expected (long-term) return on plan assets	3.89%	4.46%	3.85%
Rate of future compensation increases

PENSION AND OTHER POSTRETIREM_8

PENSION AND OTHER POSTRETIREMENT BENEFIT PLANS (Expected Benefit Payments) (Details) $ in Thousands	Dec. 31, 2020USD ($)
Pension and Other Postretirement Benefit Plans [Abstract]
2021	$ 865
2022	866
2023	895
2024	1,022
2025	1,126
Years 2026-2030	5,452
Defined Benefit Plan Expected Future Benefit Payments	$ 10,226

PENSION AND OTHER POSTRETIREM_9

PENSION AND OTHER POSTRETIREMENT BENEFIT PLANS (Fair Values of Pension Plan Assets) (Details) $ in Thousands	Dec. 31, 2020USD ($)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, fair value of plan assets	$ 31,219
Cash and Cash Equivalents [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, fair value of plan assets	757
Government Debt Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, fair value of plan assets	30,462
Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, fair value of plan assets	757
Fair Value, Inputs, Level 1 [Member] | Cash and Cash Equivalents [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, fair value of plan assets	757
Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, fair value of plan assets	30,462
Fair Value, Inputs, Level 2 [Member] | Government Debt Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, fair value of plan assets	$ 30,462

OTHER EXPENSE (Schedule of Othe

OTHER EXPENSE (Schedule of Other Nonoperating Expense) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Investment income:
Investment income - interest	$ 558	$ 2,520	$ 1,300
Net actuarial gain/(loss) on defined benefit pension plan	633	628	(902)
Write off of deferred debt issuance cost	(13,073)	(3,558)	(2,400)
Loss on extinguishment of debt	(1,197)	(1,100)	(1,295)
Other	262	567	(418)
Nonoperating Income (Expense), Total	$ (12,817)	$ (943)	$ (3,715)

2020 AND 2019 QUARTERLY RESUL_3

2020 AND 2019 QUARTERLY RESULTS OF OPERATIONS (UNAUDITED) (Schedule of Quarterly Financial Information) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Quarterly Financial Information [Line Items]
Shipping revenues	$ 56,703	$ 99,883	$ 139,725	$ 125,337	$ 124,022	$ 71,278	$ 69,010	$ 101,874	$ 421,648	$ 366,184	$ 270,361
Gain/(loss) on disposal of vessels and other property, net of impairments	(85,923)	(12,834)	(4,134)	2,804	(280)	1,472	(1,548)	48	(100,087)	(308)	(19,680)
Income/(loss) from vessel operations	(98,193)	16,832	67,892	53,349	46,621	(2,843)	(7,934)	19,324	39,880	55,168	(54,531)
Equity in income/(loss) of affiliated companies	(11,553)	5,356	5,205	5,111	(13,346)	8,474	8,015	8,070	4,119	11,213	29,432
Interest expense	(7,823)	(7,999)	(8,881)	(12,009)	(14,281)	(17,010)	(17,443)	(17,533)	(36,712)	(66,267)	(60,231)
Income tax (provision)/benefit					(1)				(1)	(1)	105
Net Income/(Loss)	$ (116,889)	$ 13,981	$ 64,358	$ 33,019	$ 15,891	$ (11,095)	$ (16,523)	$ 10,897	$ (5,531)	$ (830)	$ (88,940)
Basic and Diluted net income/(loss) per share	$ (4.18)	$ 0.50	$ 2.26	$ 1.13	$ 0.54	$ (0.38)	$ (0.57)	$ 0.37	$ (0.20)	$ (0.03)	$ (3.05)
Impairment of long-lived assets held-for-use	$ 85,900								$ 103,022		$ 19,037
Income tax expense (benefit)					$ 1				1	$ 1	$ (105)
FSO Joint Venture [Member]
Quarterly Financial Information [Line Items]
Income tax (provision)/benefit	(16,400)								(32,800)
Income tax expense (benefit)	$ 16,400								$ 32,800

CONTINGENCIES (Narrative) (Deta

CONTINGENCIES (Narrative) (Details)	12 Months Ended
	Dec. 31, 2020USD ($)
Merchant Navy Officers Pension Fund [Member]
Loss Contingencies [Line Items]
Multiemployer plans deficit amount for entity	$ 0
Merchant Navy Ratings Pension Fund [Member]
Loss Contingencies [Line Items]
Multiemployer period of performance in the past	20 years

Subsequent Events (Narrative) (

Subsequent Events (Narrative) (Details) - Subsequent Event [Member] $ in Millions	Mar. 11, 2021USD ($)property
Number of vessels in contruction | property	3
Scenario, Plan [Member]
Expected contstruction costs | $	$ 290