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Commitments and Contingencies (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011 T
Commitments and Contingencies (Textual) [Abstract]
Excess purchase obligation on additional tons of coal reserves	100,000,000
Aggregate purchase price	$ 80.0

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- Details

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Namespace Prefix:	nrp_
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- Definition

The minimum amount the entity agreed to spend under the long-term purchase commitment.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

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- Definition

Sets forth the number of units of goods that must be purchased within the specified time period of the agreement to avoid penalties or unfavorable effects on pricing, among other adverse consequences.

+ References

No definition available.

+ Details

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