SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Revenue and Voyage Expense (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Deferred revenue and revenue recognition
Accrual related to estimated customer claims	$ 359		$ 359		$ 327
Voyage expense recognition
Net gain (loss) on purchase and sale of bunker fuel and LCM adjustments	$ 1,034	$ 1,440	$ 1,889	$ 935

Represents the net gains (losses) resulting from the difference between the cost of bunker fuel delivered by the terminating charterer and the bunker fuel sold to the new charterer and the lower of cost or market adjustment to re-value bunker fuel on a quarterly basis.

No definition available.

Name:	gnk_NetGainLossOnPurchaseAndSaleOfBunkerFuelAndLowerCostOrMarketAdjustments
Namespace Prefix:	gnk_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration