CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS (Parenthetical) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS [Abstract]
Pool revenues, received from companies accounted for by the equity method	$ 71,282	$ 26,731	$ 141,957	$ 67,891

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