Debt instrument additional variable interest rate.

No definition available.

Name:	nrp_DebtInstrumentAdditionalVariableInterestRate
Namespace Prefix:	nrp_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Details

Name:	nrp_LongTermDebtTextualAbstract
Namespace Prefix:	nrp_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Maximum leverage ratio.

+ References

No definition available.

+ Details

Name:	nrp_MaximumLeverageRatio
Namespace Prefix:	nrp_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	duration

- Definition

Minimum interest coverage ratio.

+ References

No definition available.

+ Details

Name:	nrp_MinimumInterestCoverageRatio
Namespace Prefix:	nrp_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	duration

- Definition

Partnership leverage ratio.

+ References

No definition available.

+ Details

Name:	nrp_PartnershipLeverageRatio
Namespace Prefix:	nrp_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	duration

- Definition

Partnerships leverage ratio.

+ References

No definition available.

+ Details

Name:	nrp_PartnershipsLeverageRatio
Namespace Prefix:	nrp_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage of consolidated net tangible assets debt of subsidiaries not permitted to exceed.

+ References

No definition available.

+ Details

Name:	nrp_PercentageOfConsolidatedNetTangibleAssetsDebtOfSubsidiariesNotPermittedToExceed
Namespace Prefix:	nrp_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Rate of utility local improvement obligation.

+ References

No definition available.

+ Details

Name:	nrp_RateOfUtilityLocalImprovementObligation
Namespace Prefix:	nrp_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Ratio of EBITDA to consolidated fixed charges.

+ References

No definition available.

+ Details

Name:	nrp_RatioOfEbitdaToConsolidatedFixedCharges
Namespace Prefix:	nrp_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Ratio of indebtedness.

+ References

No definition available.

+ Details

Name:	nrp_RatioOfIndebtedness
Namespace Prefix:	nrp_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Decrease for amounts repaid on the debt instrument for the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Article 4

-Section 08

-Paragraph f

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 235

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.4-08.(f))

-URI http://asc.fasb.org/extlink&oid=6881521&loc=d3e23780-122690

+ Details

Name:	us-gaap_DebtInstrumentDecreaseRepayments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Interest rate stated in the contractual debt agreement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 22

-Article 5

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.22(a)(1))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_DebtInstrumentInterestRateStatedPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Details

Name:	us-gaap_DebtInstrumentLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Description of the fees for amounts available, but unused under the credit facility.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 129

-Paragraph 2, 4

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 19, 22

-Article 5

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.19(b),22(b))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_LineOfCreditFacilityCommitmentFeeDescription
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of current borrowing capacity under the credit facility considering any current restrictions on the amount that could be borrowed (for example, borrowings may be limited by the amount of current assets), but without considering any amounts currently outstanding under the facility.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 19, 22

-Article 5

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.19(b),22(b))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_LineOfCreditFacilityCurrentBorrowingCapacity
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

+ Details

Name:	us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding).

+ References

+ Details

Name:	us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The fee, expressed as a percentage of the line of credit facility, for available but unused credit capacity under the credit facility.

+ References

No definition available.

+ Details

Name:	us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Reflects the calculation as of the balance sheet date of the average interest rate weighted by the amount of short-term debt outstanding by type or by instrument at that time.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 19

-Subparagraph b

-Article 5

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.19(b))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_ShortTermDebtWeightedAverageInterestRate
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

Long-Term Debt (Details Textual) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Dec. 31, 2011	Aug. 10, 2011
Debt Instrument [Line Items]
Ratio of consolidated indebtedness	no more than 4.0 to 1.0
Long-Term Debt (Textual) [Abstract]
Floating rate revolving credit facility			$ 300
Percentage of consolidated net tangible assets debt of subsidiaries not permitted to exceed	10.00%
Ratio of EBITDA to consolidated fixed charges	not less than 3.5 to 1.0
Partnerships leverage ratio	3.75 to 1.00
Additional interest accrue	2.00%
Revolving Credit Facility Outstanding Balance	47.0	0
Maximum increase in aggregate commitment	500
Weighted average interest rate	3.68%	1.83%
Maximum leverage ratio	4.0
Minimum interest coverage ratio	3.5
Partnership leverage ratio	3.75
Senior Notes [Member]
Debt Instrument [Line Items]
Principal payments on its senior notes	$ 15.0
Credit Facility [Member]
Debt Instrument [Line Items]
Ratio of consolidated indebtedness	3.75 to 1.00
5.55% senior notes, with semi-annual interest payments in June and December, maturing June 2013 [Member]
Debt Instrument [Line Items]
Rate of Senior Notes due	5.55%
4.91% senior notes, with semi-annual interest payments in June and December, with annual principal payments in June, maturing in June 2018 [Member]
Debt Instrument [Line Items]
Rate of Senior Notes due	4.91%
8.38% senior notes, with semi-annual interest payments in March and September, with scheduled principal payments beginning March 2013, maturing in March 2019 [Member]
Debt Instrument [Line Items]
Rate of Senior Notes due	8.38%
5.05% senior notes, with semi-annual interest payments in January and July, with annual principal payments in July, maturing in July 2020 [Member]
Debt Instrument [Line Items]
Rate of Senior Notes due	5.05%
5.31% utility local improvement obligation, with annual principal and interest payments, maturing in March 2021 [Member]
Debt Instrument [Line Items]
Rate of utility local improvement obligation	5.31%
5.55% senior notes, with semi-annual interest payments in June and December, with annual principal payments in June, maturing in June 2023 [Member]
Debt Instrument [Line Items]
Rate of Senior Notes due	5.55%
5.82% senior notes, with semi-annual interest payments in March and September, with annual principal payments in March, maturing in March 2024 [Member]
Debt Instrument [Line Items]
Rate of Senior Notes due	5.82%
8.92% senior notes, with semi-annual interest payments in March and September, with scheduled principal payments beginning March 2014, maturing in March 2024 [Member]
Debt Instrument [Line Items]
Rate of Senior Notes due	8.92%
$300 million floating rate revolving credit facility, due August 2016 [Member]
Debt Instrument [Line Items]
Commitment fee on the undrawn portion of the revolving credit facility rates	0.18% to 0.40%
4.73% senior notes, with semi-annual interest payments in June and December, with scheduled principal payments beginning December 2014, maturing in December 2023 [Member]
Debt Instrument [Line Items]
Rate of Senior Notes due	4.73%
5.03% senior notes, with semi-annual interest payments in June and December, with scheduled principal payments beginning December 2014, maturing in December 2026 [Member]
Debt Instrument [Line Items]
Rate of Senior Notes due	5.03%
5.18% senior notes, with semi-annual interest payments in June and December, with scheduled principal payments beginning December 2014, maturing in December 2026 [Member]
Debt Instrument [Line Items]
Rate of Senior Notes due	5.18%
Maximum [Member]
Debt Instrument [Line Items]
Revolving credit facility	0.40%
Minimum [Member]
Debt Instrument [Line Items]
Revolving credit facility	0.18%