DERIVATIVE INSTRUMENTS (Details 4) lb in Millions	Dec. 31, 2017 lb oz	Dec. 31, 2016 lb oz
Volumes subject to final pricing net of outstanding swaps [Abstract]
Gold ounces \| oz	2,000	4,000
Copper pounds \| lb	1.6	3.0

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

No definition available.

Name:	ngd_VolumeOfCopperSubjectToFinalPricingNetOfOutstandingSwaps
Namespace Prefix:	ngd_
Data Type:	num:massItemType
Balance Type:	na
Period Type:	instant