CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS (Parenthetical) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019
CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS [Abstract]
Pool revenues, received from companies accounted for by the equity method	$ 70,675	$ 41,160

venues earned from Pools that are equity method investments.

No definition available.

Name:	insw_EquityMethodInvestmentSummarizedFinancialInformationShippingPoolRevenue
Namespace Prefix:	insw_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration