Derivative instruments - Impact of movements in market commodity prices (Details) oz in Millions, lb in Millions	Dec. 31, 2022 lb oz	Dec. 31, 2021 lb oz
Financial Instruments [Abstract]
Gold ounces \| oz	0.5	0.7
Copper pounds \| lb	1.4	1.0

The volume of copper subject to final pricing net of outstanding swaps.

No definition available.

Name:	ngd_VolumeOfCopperSubjectToFinalPricingNetOfOutstandingSwaps
Namespace Prefix:	ngd_
Data Type:	dtr-types:massItemType
Balance Type:	na
Period Type:	instant