Natural Resource Partners (NRP) 10-Q 8 May 15 2015 Q1 Quarterly report Financial data

Document_and_Entity_Informatio

Document and Entity Information	3 Months Ended
	Mar. 31, 2015	7-May-15
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	FALSE
Document Period End Date	31-Mar-15
Document Fiscal Year Focus	2015
Document Fiscal Period Focus	Q1
Trading Symbol	NRP
Entity Registrant Name	NATURAL RESOURCE PARTNERS LP
Entity Central Index Key	1171486
Current Fiscal Year End Date	-19
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		122,299,825

Consolidated_Balance_Sheets

Consolidated Balance Sheets (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Thousands, unless otherwise specified
Current assets:
Cash and cash equivalents	$33,275	$50,076
Accounts receivable, net	52,323	66,455
Accounts receivable - affiliate	5,851	9,494
Inventory	5,790	5,814
Prepaid expenses and other	4,154	4,279
Total current assets	101,393	136,118
Land	25,243	25,243
Plant and equipment, net	78,584	60,093
Mineral rights, net	1,773,449	1,781,852
Intangible assets, net	59,713	60,733
Equity in unconsolidated investment	262,722	264,020
Long-term contracts receivable - affiliate	49,610	50,008
Goodwill	29,465	52,012
Other assets	13,746	14,645
Total assets	2,393,925	2,444,724
Current liabilities:
Accounts payable	16,862	22,465
Accounts payable - affiliates	936	950
Accrued liabilities	50,772	43,533
Current portion of long-term debt	155,983	80,983
Total current liabilities	224,553	147,931
Deferred revenue	79,052	73,207
Deferred revenue - affiliates	86,315	87,053
Long-term debt, net	1,283,352	1,374,336
Long-term debt, net - affiliate	19,911	19,904
Other non-current liabilities	8,403	22,138
Partners' Capital:
Common unitholders' interest (122,299,825 units outstanding)	683,354	709,019
General partner's interest	11,721	12,245
Accumulated other comprehensive loss	-1,424	-459
Total partners' capital	693,651	720,805
Non-controlling interest	-1,312	-650
Total capital	692,339	720,155
Total liabilities and capital	$2,393,925	$2,444,724

Consolidated_Balance_Sheets_Pa

Consolidated Balance Sheets (Parenthetical)	Mar. 31, 2015	Dec. 31, 2014
Statement of Financial Position [Abstract]
Common units outstanding	122,299,825	122,299,825

Consolidated_Statements_of_Com

Consolidated Statements of Comprehensive Income (Unaudited) (USD $)	3 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Revenues and other income:
Coal related revenues	$30,421	$33,646
Coal related revenues - affiliates	19,061	18,727
Aggregates related revenues	28,946	3,396
Oil and gas related revenues	15,230	10,058
Equity in earnings of unconsolidated investment	12,523	9,779
Property taxes	3,004	3,967
Other	492	736
Total revenues and other income	109,677	80,309
Costs and expenses:
Coal related expenses	1,321	577
Aggregates related expenses	22,407	73
Oil and gas related expenses	3,762	1,921
General and administrative	7,454	2,690
General and administrative - affiliates	3,786	3,094
Depreciation, depletion and amortization	25,392	14,647
Property, franchise and other taxes	5,138	4,868
Total operating expenses	69,260	27,870
Income from operations	40,417	52,439
Other income (expense)
Interest expense	-22,943	-19,860
Interest income	15	26
Other expense, net	-22,928	-19,834
Net income	17,489	32,605
Less: net income attributable to non-controlling interest	0	0
Net income attributable to NRP	17,489	32,605
Net income attributable to partners:
Limited partners	17,139	31,953
General partner	350	652
Basic and diluted net income per common unit	$0.14	$0.29
Weighted average number of common units outstanding	122,300	109,848
Net income	17,489	32,605
Comprehensive loss from unconsolidated investment and other	-965	-101
Comprehensive income attributable to NRP	$16,524	$32,504

Consolidated_Statements_of_Cas

Consolidated Statements of Cash Flows (Unaudited) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Cash flows from operating activities:
Net income	$17,489	$32,605
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation, depletion and amortization	25,392	14,647
Equity earnings from unconsolidated investment	-12,523	-9,779
Distributions from equity earnings from unconsolidated investment	10,903	11,645
Other, net	-1,010	747
Other, net - affiliates	7
Change in operating assets and liabilities
Accounts receivable	15,110	-4,262
Accounts receivable - affiliates	3,643	-3,098
Accounts payable	-2,642	-1,568
Accounts payable - affiliates	-14	478
Accrued liabilities	921	1,256
Deferred revenue	5,845	330
Deferred revenue - affiliates	-738	3,412
Accrued incentive plan expenses	-6,275	-8,065
Other items, net	103	-18
Other items, net - affiliates	-739	300
Net cash provided by operating activities	55,472	38,630
Cash flows from investing activities:
Acquisition of mineral rights	-16,788	-1,804
Acquisition of plant and equipment	-1,365
Proceeds from sale of mineral rights	4,261
Proceeds from sale of plant and equipment	905
Return on direct financing lease and contractual override - affiliate	1,137	297
Net cash used in investing activities	-11,850	-1,507
Cash flows from financing activities:
Proceeds from loans	25,000	2,000
Repayment of loans	-41,166	-41,166
Proceeds from issuance of common units		4,513
Capital contribution by general partner		92
Distributions to non-controlling interest	-662	-974
Distributions to partners	-43,678	-39,218
Other	83	-57
Net cash used in financing activities	-60,423	-74,810
Net decrease in cash and cash equivalents	-16,801	-37,687
Cash and cash equivalents at beginning of period	50,076	92,513
Cash and cash equivalents at end of period	33,275	54,826
Supplemental cash flow information:
Cash paid during the period for interest	14,344	14,703
Plant, equipment and mineral rights funded with accounts payable or accrued liabilities	$3,761

Consolidated_Statements_of_Par

Consolidated Statements of Partners' Capital (Unaudited) (USD $)	Total	General Partner [Member]	Common Stock [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Partners' Capital Excluding Non-Controlling Interest [Member]	Non-Controlling Interest [Member]
In Thousands
Balance at Dec. 31, 2014	$720,805	$12,245	$709,019	($459)	$720,805	($650)
Balance, units at Dec. 31, 2014			122,300
Distributions to unitholders	-43,678	-874	-42,804		-43,678
Distributions to non-controlling interest	-662					-662
Net income	17,489	350	17,139		17,489
Comprehensive loss from unconsolidated investment and other	-965			-965	-965
Balance at Mar. 31, 2015	$693,651	$11,721	$683,354	($1,424)	$693,651	($1,312)
Balance, units at Mar. 31, 2015			122,300

Basis_of_Presentation

Basis of Presentation	3 Months Ended
	Mar. 31, 2015
Accounting Policies [Abstract]
Basis of Presentation	1	Basis of Presentation
	Nature of Business
	Natural Resource Partners L.P. (the “Partnership”) engages principally in the business of owning, operating, managing and leasing a diversified portfolio of mineral properties in the United States, including interests in coal, trona and soda ash, oil and gas, construction aggregates, frac sand and other natural resources. As used in these Notes to Consolidated Financial Statements, the terms “NRP,” “we,” “us” and “our” refer to Natural Resource Partners L.P. and its subsidiaries, unless otherwise stated or indicated by context.
	Principles of Consolidation and Reporting
	The accompanying unaudited Consolidated Financial Statements of the “Partnership” have been prepared in accordance with generally accepted accounting principles in the United States of America (“GAAP”) for interim financial information and with Rule 10-01 of Regulation S-X. Accordingly, they do not include all of the information and footnotes required by GAAP for complete financial statements. Certain prior period amounts have been reclassified to conform to the current period presentation. The reclassifications had no effect on the Partnership’s overall consolidated financial position, income or cash flows. In our opinion, all adjustments, consisting only of normal recurring adjustments necessary for a fair presentation, have been included. The interim financial statements should be read in conjunction with the audited financial statements and related notes included in the Partnership’s Annual Report on Form 10-K for the year ended December 31, 2014. Interim results are not necessarily indicative of the results for a full year.
	In March 2015, the Partnership recorded an out-of-period adjustment to correct an error in depletion expense related to its oil and gas royalty interests owned by BRP LLC, a joint venture with International Paper Company in which the Partnership owns a 51% interest. Depletion expense for the three months ended March 31, 2015 included a credit of $3.8 million to adjust the impact of depletion expense recorded in prior periods. After evaluating the quantitative and qualitative aspects of the error and the out-of-period adjustment to the Partnership’s financial results, management has determined that the misstatement and the out-of-period adjustment are not material to the prior period financial statements.
	Recently Issued Accounting Standards
	In May 2014, the Financial Accounting Standards Board (“FASB”) amended its guidance on revenue recognition. The core principle of this amendment is that an entity should recognize revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. This guidance is effective for annual reporting periods beginning after December 15, 2016, including interim periods within that reporting period, with earlier adoption not permitted. This guidance can be adopted either retrospectively to each prior reporting period presented or as a cumulative-effect adjustment as of the date of adoption. We are currently evaluating the impact of the provisions of this guidance on our consolidated financial position, results of operations and cash flows.
	In April 2015, the FASB issued authoritative guidance which changes the presentation of debt issuance costs in financial statements. This guidance requires an entity to present such costs in the balance sheet as a direct deduction from the related debt liability rather than as an asset. Amortization of the costs will continue to be reported as interest expense. This guidance is effective for annual reporting periods beginning after December 15, 2016. Early adoption is permitted. This guidance will be applied retrospectively to each prior period presented. We are currently evaluating the impact of the provisions of this guidance on our consolidated balance sheets.

Acquisitions

Acquisitions	3 Months Ended
	Mar. 31, 2015
Business Combinations [Abstract]
Acquisitions	2	Acquisitions
	VantaCore Acquisition
	On October 1, 2014, the Partnership completed its acquisition of VantaCore Partners LLC (“VantaCore”), a privately held company specializing in the construction materials industry, for $201.1 million in cash and common units. Headquartered in Philadelphia, Pennsylvania, VantaCore operates three hard rock quarries, five sand and gravel plants, two asphalt plants and a marine terminal. VantaCore’s current operations are located in Pennsylvania, West Virginia, Tennessee, Kentucky and Louisiana.
	The Partnership accounted for the transaction under the acquisition method of accounting. Accordingly, the Partnership conducted assessments of net assets acquired and recognized amounts for identifiable assets acquired and liabilities assumed at their estimated fair values on the acquisition date, while transaction and integration costs associated with the acquisitions were expensed as incurred. The accounting for the VantaCore acquisition is not complete and adjustments to provisional amounts, or recognition of additional assets acquired or liabilities assumed may occur as more detailed analyses are completed and additional information is obtained about the facts and circumstances that existed as of the acquisition date. The results of operations of the acquisition have been included in our consolidated financial statements since the acquisition date.
	In the first quarter 2015, the purchase price allocation was adjusted as more detailed analysis was completed and additional information was obtained about the facts and circumstances for various items of VantaCore’s plant and equipment that existed as of acquisition date. As a result of this adjustment, plant and equipment was increased by $22.5 million with a corresponding decrease to goodwill.
	Sanish Field Acquisition
	On November 12, 2014, the Partnership acquired non-operated oil and gas working interests in the Sanish Field of the Williston Basin from an affiliate of Kaiser-Francis Oil Company for $339.1 million.
	The Partnership accounted for the transaction under the acquisition method of accounting. Accordingly, the Partnership conducted assessments of net assets acquired and recognized amounts for identifiable assets acquired and liabilities assumed at their estimated fair values on the acquisition date, while transaction and integration costs associated with the acquisitions were expensed as incurred. The accounting for the Sanish Field acquisition is not complete and adjustments to provisional amounts, or recognition of additional assets acquired or liabilities assumed, may occur as more detailed analyses are completed and additional information is obtained about the facts and circumstances that existed as of the acquisition date. The results of operations of the acquisition have been included in our consolidated financial statements since the acquisition date.
	Pro Forma Financial Information
	The following unaudited pro forma financial information presents a summary of the Partnership’s consolidated results of operations for the three months ended March 31, 2014, assuming the VantaCore and Sanish Field acquisitions had been completed as of January 1, 2014, including adjustments to reflect the values assigned to the net assets acquired:
			Three Months
			Ended March 31,
			2014
			(Unaudited)
			(In thousands)
	Revenue and other income except aggregates and oil and gas related revenues		$	66,876
	Aggregates related revenues			33,166
	Oil and gas related revenues			27,892
	Total revenue		$	127,934
	Net income		$	33,210
	Basic and diluted net income per common unit		$	0.3

Equity_Investment

Equity Investment	3 Months Ended
	Mar. 31, 2015
Equity Method Investments and Joint Ventures [Abstract]
Equity Investment	3	Equity Investment
	We account for our 49% investment in OCI Wyoming LLC (“OCI Wyoming”) using the equity method of accounting. In the three months ended March 31, 2015 and 2014, OCI Wyoming distributed $10.9 million and $11.6 million to us, respectively. The income allocated to NRP’s equity interests and amortization of fair value adjustments are summarized as follows (in thousands):
			Three Months Ended
			March 31,
			2015			2014
			(Unaudited)
	Income allocation to NRP’s equity interests		$	13,727		$	11,276
	Amortization of basis difference		$	(1,204	)	$	(1,497	)
	Equity in earnings of unconsolidated investment		$	12,523		$	9,779
	The financial position of OCI Wyoming at March 31, 2015 and December 31, 2014 and the results of OCI Wyoming’s operations for the three months ended March 31, 2015 and 2014 are summarized as follows (in thousands):
			Three Months Ended
			March 31,
			2015			2014
			(Unaudited)
	Sales		$	120,430		$	116,240
	Gross profit		$	32,724		$	27,119
	Net income		$	28,014		$	23,012
			March 31,			December 31,
			2015			2014
			(Unaudited)
	Current assets		$	203,953		$	200,622
	Noncurrent assets		$	201,746		$	202,282
	Current liabilities		$	46,656		$	47,704
	Noncurrent liabilities		$	149,262		$	149,192
	The difference between the amount at which our investment in OCI Wyoming is carried and the amount of underlying equity in OCI Wyoming’s net assets was $160.5 million and $162.7 million as of March 31, 2015 and December 31, 2014, respectively. The excess that relates to property, plant and equipment is being amortized into income over a weighted average of 28 years. The excess that relates to a right to mine asset is being amortized into income using the units of production method.
	The purchase agreement for the acquisition of our interest in OCI Wyoming requires us to pay additional contingent consideration to Anadarko to the extent certain performance criteria described in the purchase agreement are met at OCI Wyoming in any of the years 2013, 2014 or 2015. During the first quarter of 2015, the Partnership paid $3.8 million in contingent consideration to Anadarko, and during the first quarter of 2014 the Partnership paid $0.5 million in contingent consideration. As of March 31, 2015, the Partnership has estimated and recorded $8.8 million as an accrued liability payable in the first quarter of 2016 with respect to 2015. The Partnership has no obligation to pay contingent consideration with respect to any period after 2015.

Plant_and_Equipment

Plant and Equipment	3 Months Ended
	Mar. 31, 2015
Property, Plant and Equipment [Abstract]
Plant and Equipment	4	Plant and Equipment
	The Partnership’s plant and equipment consist of the following (in thousands):
			March 31,			December 31,
			2015			2014
			(Unaudited)
	Plant and equipment at cost		$	111,266		$	89,759
	Construction in process			141			457
	Less accumulated depreciation			(32,823	)		(30,123	)
	Total plant and equipment, net		$	78,584		$	60,093
	Depreciation and amortization expense related to our plant and equipment totaled $4.5 million and $1.3 million for the three months ended March 31, 2015 and 2014, respectively.

Mineral_Rights

Mineral Rights	3 Months Ended
	Mar. 31, 2015
Extractive Industries [Abstract]
Mineral Rights	5	Mineral Rights
	The Partnership’s mineral rights consist of the following (in thousands):
			March 31,			December 31,
			2015			2014
			(Unaudited)
	Coal		$	1,541,343		$	1,541,572
	Oil and Gas			570,195			560,395
	Aggregates			212,690			211,490
	Other			15,014			15,014
	Less accumulated depletion and amortization			(565,793	)		(546,619	)
	Total mineral rights, net		$	1,773,449		$	1,781,852
	Depletion and amortization expense related to our mineral rights totaled $19.9 million and $12.5 million for the three months ended March 31, 2015 and 2014, respectively.

Intangible_Assets

Intangible Assets	3 Months Ended
	Mar. 31, 2015
Goodwill and Intangible Assets Disclosure [Abstract]
Intangible Assets	6	Intangible Assets
	Amounts recorded as intangible assets along with the balances and accumulated amortization are reflected in the table below (in thousands):
			March 31,			December 31,
			2015			2014
			(Unaudited)
	Contract intangibles		$	82,972		$	82,972
	Other intangibles			3,004			3,004
	Less accumulated amortization			(26,263	)		(25,243	)
	Total intangible assets, net		$	59,713		$	60,733
	Amortization expense related to our intangible assets totaled $1.0 million and $0.8 million for the three months ended March 31, 2015 and 2014, respectively.

Debt_and_DebtAffiliate

Debt and Debt-Affiliate	3 Months Ended
	Mar. 31, 2015
Debt Disclosure [Abstract]
Debt and Debt-Affiliate
	7	Debt and Debt—Affiliate
	As used in this Note 7, references to “NRP LP” refer to Natural Resource Partners L.P. only, and not to NRP (Operating) LLC, a wholly owned subsidiary of NRP LP, or any of Natural Resource Partners L.P.’s subsidiaries. References to “Opco” refer to NRP (Operating) LLC and its subsidiaries. References to NRP Oil and Gas refer to NRP Oil and Gas LLC, a wholly owned subsidiary of NRP LP. NRP Finance Corporation (“NRP Finance”) is a wholly owned subsidiary of NRP LP and a co-issuer with NRP LP on the 9.125% senior notes described below.
	As of March 31, 2015 and December 31, 2014, debt and debt—affiliate consisted of the following (in thousands):
			March 31,			December 31,
			2015			2014
			(Unaudited)
	NRP LP Debt:
	$425 million 9.125% senior notes, with semi-annual interest payments in April and October, maturing October 2018, $300 million issued at 99.007% and $125 million issued at 99.5%		$	422,356		$	422,167
	Opco Debt:
	$300 million floating rate revolving credit facility, due August 2016			225,000			200,000
	$200 million floating rate term loan, due January 2016			75,000			75,000
	4.91% senior notes, with semi-annual interest payments in June and December, with annual principal payments in June, maturing in June 2018			18,467			18,467
	8.38% senior notes, with semi-annual interest payments in March and September, with annual principal payments in March, maturing in March 2019			85,714			107,143
	5.05% senior notes, with semi-annual interest payments in January and July, with annual principal payments in July, maturing in July 2020			46,154			46,154
	5.31% utility local improvement obligation, with annual principal and interest payments, maturing in March 2021			1,153			1,345
	5.55% senior notes, with semi-annual interest payments in June and December, with annual principal payments in June, maturing in June 2023			24,300			24,300
	4.73% senior notes, with semi-annual interest payments in June and December, with annual principal payments in December, maturing in December 2023			67,500			67,500
	5.82% senior notes, with semi-annual interest payments in March and September, with annual principal payments in March, maturing in March 2024			135,000			150,000
	8.92% senior notes, with semi-annual interest payments in March and September, with annual principal payments in March, maturing in March 2024			40,910			45,455
	5.03% senior notes, with semi-annual interest payments in June and December, with annual principal payments in December, maturing in December 2026			161,538			161,538
	5.18% senior notes, with semi-annual interest payments in June and December, with annual principal payments in December, maturing in December 2026			46,154			46,154
	NRP Oil and Gas Debt:
	Reserve-based revolving credit facility due 2019			110,000			110,000
	Total debt and debt – affiliate			1,459,246			1,475,223
	Less: current portion of long-term debt			(155,983	)		(80,983	)
	Total long-term debt and debt – affiliate		$	1,303,263		$	1,394,240
	NRP LP Debt
	Senior Notes
	In September 2013, NRP LP, together with NRP Finance as co-issuer, issued $300 million of 9.125% Senior Notes due 2018 at an offering price of 99.007% of par. Net proceeds after expenses from the issuance of the senior notes were approximately $289.0 million. The senior notes call for semi-annual interest payments on April 1 and October 1 of each year, and will mature on October 1, 2018.
	In October 2014, NRP LP, together with NRP Finance as co-issuer, issued an additional $125 million of its 9.125% Senior Notes due 2018 at an offering price of 99.5% of par. The notes constitute the same series of securities as the existing $300.0 million 9.125% senior notes due 2018 issued in September 2013. Net proceeds of $122.6 million from the additional issuance of the Senior Notes were used to fund a portion of the purchase price of NRP’s acquisition of non-operated working interests in oil and gas assets located in the Williston Basin in North Dakota. The notes call for semi-annual interest payments on April 1 and October 1 of each year and will mature on October 1, 2018.
	The indenture for the senior notes contains covenants that, among other things, limit the ability of NRP LP and certain of its subsidiaries to incur or guarantee additional indebtedness. Under the indenture, NRP LP and certain of its subsidiaries generally are not permitted to incur additional indebtedness unless, on a consolidated basis, the fixed charge coverage ratio (as defined in the indenture) is at least 2.0 to 1.0 for the four preceding full fiscal quarters. The ability of NRP LP and certain of its subsidiaries to incur additional indebtedness is further limited in the event the amount of indebtedness of NRP LP and certain of its subsidiaries that is senior to NRP LP’s unsecured indebtedness exceeds certain thresholds.
	Opco Debt
	All of Opco’s debt is guaranteed by its wholly owned subsidiaries. As of March 31, 2015 and December 31, 2014, Opco was in compliance with the terms of the financial covenants contained in its debt agreements.
	Senior Notes
	Opco made principal payments of $41.0 million on its senior notes during each of the three months ended March 31, 2015 and 2014. The Opco senior note purchase agreement contains covenants requiring Opco to:
		•		maintain a ratio of consolidated indebtedness to consolidated EBITDDA (as defined in the note purchase agreement) of no more than 4.0 to 1.0 for the four most recent quarters;
		•		not permit debt secured by certain liens and debt of subsidiaries to exceed 10% of consolidated net tangible assets (as defined in the note purchase agreement); and
		•		maintain the ratio of consolidated EBITDDA (as defined in the note purchase agreement) to consolidated fixed charges (consisting of consolidated interest expense and consolidated operating lease expense) at not less than 3.5 to 1.0.
	The 8.38% and 8.92% senior notes also provide that in the event that Opco’s leverage ratio of consolidated indebtedness to consolidated EBITDDA (as defined in the note purchase agreement) exceeds 3.75 to 1.00 at the end of any fiscal quarter, then in addition to all other interest accruing on these notes, additional interest in the amount of 2.00% per annum shall accrue on the notes for the two succeeding quarters and for as long thereafter as the leverage ratio remains above 3.75 to 1.00.
	Revolving Credit Facility
	The weighted average interest rates for the debt outstanding under Opco’s revolving credit facility for the three months ended March 31, 2015 and 2014 were 1.94% and 1.98%, respectively. Opco incurs a commitment fee on the undrawn portion of the revolving credit facility at rates ranging from 0.18% to 0.40% per annum. The facility includes an accordion feature whereby Opco may request its lenders to increase their aggregate commitment to a maximum of $500 million on the same terms.
	Opco’s revolving credit facility contains covenants requiring Opco to maintain:
		•		a ratio of consolidated indebtedness to consolidated EBITDDA (as defined in the credit agreement) not to exceed 4.0 to 1.0 and,
		•		a ratio of consolidated EBITDDA (as defined in the credit agreement) to consolidated fixed charges (consisting of consolidated interest expense and consolidated lease operating expense) of not less than 3.5 to 1.0 for the four most recent quarters.
	Term Loan Facility
	During 2013, Opco issued $200 million in term debt. The weighted average interest rates for the debt outstanding under the term loan for the three months ended March 31, 2015 and 2014 were 2.19% and 2.25% respectively. Opco repaid $101.0 million in principal under the term loan during the third quarter of 2013 and an additional $24.0 million during the fourth quarter of 2014. Repayment terms call for the remaining outstanding balance of $75.0 million to be paid on January 23, 2016.
	Opco’s term loan contains covenants requiring Opco to maintain:
		•		a ratio of consolidated indebtedness to consolidated EBITDDA (as defined in the credit agreement) not to exceed 4.0 to 1.0 and,
		•		a ratio of consolidated EBITDDA to consolidated fixed charges (consisting of consolidated interest expense and consolidated lease operating expense) of not less than 3.5 to 1.0 for the four most recent quarters.
	NRP Oil and Gas Debt
	Revolving Credit Facility
	In August 2013, NRP Oil and Gas entered into a 5-year, $100 million senior secured, reserve-based revolving credit facility in order to fund capital expenditure requirements related to the development of the oil and gas assets in which it owns non-operated working interests. In connection with the closing of the Sanish Field acquisition in November 2014, the credit facility was amended to increase its size to $500 million with an initial borrowing base of $137 million. The maturity date of the credit facility is November 12, 2019. The credit facility is secured by a first priority lien and security interest in substantially all of the assets of NRP Oil and Gas. NRP Oil and Gas is the sole obligor under its revolving credit facility, and neither the Partnership nor any of its other subsidiaries is a guarantor of such facility. At both March 31, 2015 and December 31, 2014, there was $110.0 million outstanding under the credit facility. The weighted average interest rate for the debt outstanding under the credit facility for each of the three months ended March 31, 2015 and 2014 was 2.43% and 1.91%, respectively.
	Indebtedness under the NRP Oil and Gas credit facility bears interest, at the option of NRP Oil and Gas, at either:
		•		the higher of (i) the prime rate as announced by the agent bank; (ii) the federal funds rate plus 0.50%; or (iii) LIBOR plus 1%, in each case plus an applicable margin ranging from 0.50% to 1.50%; or
		•		a rate equal to LIBOR, plus an applicable margin ranging from 1.50% to 2.50%.
	NRP Oil and Gas incurs a commitment fee on the unused portion of the borrowing base under the credit facility at a rate ranging from 0.375% to 0.50% per annum.
	The NRP Oil and Gas credit facility contains certain covenants, which, among other things, require the maintenance of:
		•		a total leverage ratio (defined as the ratio of the total debt of NRP Oil and Gas to its EBITDAX) of not more than 3.5 to 1.0; and
		•		a minimum current ratio of 1.0 to 1.0.
	As of March 31, 2015 and December 31, 2014, NRP Oil and Gas was in compliance with the terms of the financial covenants contained in its credit facility.
	The maximum amount available under the credit facility is subject to semi-annual redeterminations of the borrowing base in May and November of each year, based on the value of the proved oil and natural gas reserves of NRP Oil and Gas, in accordance with the lenders’ customary procedures and practices. NRP Oil and Gas and the lenders each have a right to one additional redetermination each year.

Fair_Value_Measurements

Fair Value Measurements	3 Months Ended
	Mar. 31, 2015
Fair Value Disclosures [Abstract]
Fair Value Measurements	8	Fair Value Measurements
	The Partnership’s financial instruments consist of cash and cash equivalents, accounts receivable, accounts payable and long-term debt. The carrying amounts reported on our Consolidated Balance Sheets for cash and cash equivalents, accounts receivable and accounts payable approximate fair value due to their short-term nature. The following table (in thousands) shows the carrying amount and estimated fair value of our other financial instruments:
			March 31, 2015				December 31, 2014
			Carrying		Estimated		Carrying		Estimated
			Amount		Fair Value		Amount		Fair Value
			(Unaudited)
	Assets
	Contracts receivable – affiliate, current and long-term(3)		$	4,646	$	5,041	$	4,870	$	5,162
	Debt and debt – affiliate
	NRP LP senior notes(1)		$	422,356	$	416,957	$	422,167	$	423,780
	Opco revolving credit facility and term loan facility(2)		$	300,000	$	300,000	$	275,000	$	275,000
	Opco senior notes and utility local improvement obligation(3)		$	626,890	$	629,521	$	668,056	$	672,740
	NRP Oil and Gas revolving credit facility(2)		$	110,000	$	110,000	$	110,000	$	110,000
	(1)	The Level 2 estimated fair value was based upon quotations obtained for similar instruments on the closing trading prices near quarter end.
	(2)	The Level 3 estimated fair value approximates the carrying amount because the interest rates are variable and reflective of market rates and the Partnership has the ability to repay this debt at any time without penalty.
	(3)	The Level 3 estimated fair value was based on comparable term risk-free treasury issues with a market rate component determined by current financial instruments with similar characteristics.

Related_Party_Transactions

Related Party Transactions	3 Months Ended
	Mar. 31, 2015
Related Party Transactions [Abstract]
Related Party Transactions	9	Related Party Transactions
	Reimbursements to Affiliates of our General Partner
	The Partnership’s general partner does not receive any management fee or other compensation for its management of Natural Resource Partners L.P. However, in accordance with the partnership agreement, the general partner and its affiliates are reimbursed for expenses incurred on the Partnership’s behalf. All direct general and administrative expenses are charged to the Partnership as incurred. The Partnership also reimburses indirect general and administrative costs, including certain legal, accounting, treasury, information technology, insurance, administration of employee benefits and other corporate services incurred by our general partner and its affiliates, Quintana Minerals Corporation and Western Pocahontas Properties Limited Partnership. The Partnership had accounts payable—affiliate to Quintana Minerals Corporation of $0.6 million at both March 31, 2015 and December 31, 2014, for services provided by Quintana to the Partnership. The Partnership had accounts payable—affiliate to Western Pocahontas of $0.3 million and $0.4 million at March 31, 2015 and December 31, 2015, respectively.
	The reimbursements to affiliates of the Partnership’s general partner for services performed by Western Pocahontas Properties and Quintana Minerals Corporation are as follows (in thousands):
			Three Months Ended
			March 31,
			2015		2014
			(Unaudited)
	General and administrative—affiliate		$	3,786	$	3,094
	The Partnership also leases an office building in Huntington, West Virginia from Western Pocahontas Properties and recorded $0.2 million in general and administrative—affiliate in each of the three months ended March 31, 2015 and 2014.
	Cline Affiliates
	Various companies controlled by Chris Cline, including Foresight Energy LP, lease coal reserves from the Partnership, and the Partnership provides coal transportation services to them for a fee. Mr. Cline, both individually and through another affiliate, Adena Minerals, LLC, owns a 31% interest in NRP’s general partner, as well as approximately 4.9 million of NRP’s common units. Coal related revenues from Cline affiliates totaled $18.3 million and $17.9 million for the three months ended March 31, 2015 and 2014, respectively. As of March 31, 2015 and December 31, 2014 the Partnership had accounts receivable-affiliates from Cline affiliates of $5.6 million and $9.2 million, respectively. As of March 31, 2015, the Partnership had recorded $86.1 million in minimum royalty payments to date that have not been recouped by Foresight Energy.
	The Partnership entered into a lease agreement related to the rail loadout and associated facilities at Foresight Energy’s Sugar Camp mine that has been accounted for as a direct financing lease. Total projected remaining payments under the lease at March 31, 2015 are $85.0 million with unearned income of $38.1 million, and the net amount receivable was $46.9 million, of which $1.8 million is included in Accounts receivable—affiliates while the remaining is included in Long-term contracts receivable—affiliate. Total projected remaining payments under the lease at December 31, 2014 were $86.3 million with unearned income of $39.0 million and the net amount receivable was $47.3 million, of which $1.8 million is included in Accounts receivable—affiliates while the remaining is included in Long-term contracts receivable—affiliate on the accompanying Consolidated Balance Sheets.
	In a separate transaction, the Partnership acquired a contractual overriding royalty interest from a subsidiary of Foresight Energy that will provide for payments based upon production from specific tons at the Sugar Camp operations. This overriding royalty was accounted for as a financing arrangement and is reflected as an affiliate receivable. The net amount receivable under the agreement as of March 31, 2015 was $4.6 million, of which $0.2 million is included in Accounts receivable—affiliates while the remaining is included in Long-term contracts receivable—affiliate. The net amount receivable under the agreement as of December 31, 2014 was $5.6 million, of which $1.1 million is included in Accounts receivable—affiliates while the remaining is included in Long-term contracts receivable—affiliate on the accompanying Consolidated Balance Sheets.
	Long-Term Debt—Affiliate
	Donald R. Holcomb, one of the Partnership’s directors, is a manager of Cline Trust Company, LLC, which owns approximately 5.35 million of the Partnership’s common units and $20.0 million in principal amount of the Partnership’s 9.125% Senior Notes due 2018. The members of the Cline Trust Company are four trusts for the benefit of the children of Christopher Cline, each of which owns an approximately equal membership interest in the Cline Trust Company. Mr. Holcomb also serves as trustee of each of the four trusts. Cline Trust Company, LLC purchased the $20.0 million of the Partnership’s 9.125% Senior Notes due 2018 in the Partnership’s offering of $125.0 million additional principal amount of such notes in October 2014 at the same price as the other purchasers in that offering. The balance on this portion of the Partnership’s 9.125% Senior Notes due 2018 was $19.9 million as of March 31, 2015 and is included in Long-term debt – affiliate.
	Quintana Capital Group GP, Ltd.
	Corbin J. Robertson, Jr. is a principal in Quintana Capital Group GP, Ltd., which controls several private equity funds focused on investments in the energy business. In connection with the formation of Quintana Capital, the Partnership adopted a formal conflicts policy that establishes the opportunities that will be pursued by the Partnership and those that will be pursued by Quintana Capital. The governance documents of Quintana Capital’s affiliated investment funds reflect the guidelines set forth in the Partnership’s conflicts policy.
	At March 31, 2015, a fund controlled by Quintana Capital owned a majority interest in Corsa Coal Corp. (“Corsa”), a coal mining company traded on the TSX Venture Exchange that is one of the Partnership’s lessees in Tennessee. Corbin J. Robertson III, one of the Partnership’s directors, is Chairman of the Board of Corsa. Coal related revenues from Corsa totaled $0.8 million and $0.9 million for the three months ended March 31, 2015 and 2014, respectively.
	As of March 31, 2015, the Partnership had recorded $0.2 million in minimum royalty payments to date that have not been recouped by Corsa. The Partnership also had accounts receivable—affiliate totaling $0.2 million and $0.3 million from Corsa at March 31, 2015 and December 31, 2014, respectively.

Major_Lessees

Major Lessees	3 Months Ended
	Mar. 31, 2015
Risks and Uncertainties [Abstract]
Major Lessees	10	Major Lessees
	Revenues from lessees that exceeded ten percent of total revenues and other income for the periods are presented below (in thousands except for percentages):
			Three Months Ended
			March 31,
			2015					2014
			(Unaudited)
			Revenues		Percent			Revenues		Percent
	Foresight Energy and affiliates		$	18,298		17	%	$	17,882		22	%
	Alpha Natural Resources		$	8,829		8	%	$	11,642		14	%
	For the three months ended March 31, 2015, the Partnership derived over 25% of its total revenues and other income from the two companies listed above. The Partnership has a significant concentration of revenues with Foresight Energy and Alpha, although in most cases, with the exception of Foresight Energy’s Williamson mine, the exposure is spread out over a number of different mining operations and leases. Foresight Energy’s Williamson mine was responsible for approximately 5% and 11% of the Partnership’s total revenues and other income for the three months ended March 31, 2015 and 2014, respectively.

LongTerm_Incentive_Plans

Long-Term Incentive Plans	3 Months Ended
	Mar. 31, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Long-Term Incentive Plans
	11	Long-Term Incentive Plans
	GP Natural Resource Partners LLC adopted the Natural Resource Partners Long-Term Incentive Plan (the “Long-Term Incentive Plan”) for directors of GP Natural Resource Partners LLC and employees of its affiliates who perform services for the Partnership. Under the plan a grantee will receive the market value of a common unit in cash upon vesting. A summary of activity in the outstanding grants during 2015 is as follows:
			(Unaudited)
	Outstanding grants at January 1, 2015			1,153,393
	Grants during the year			468,486
	Grants vested and paid during the year			(290,430	)
	Forfeitures during the year			—
	Outstanding grants at March 31, 2015			1,331,449
	Grants typically vest at the end of a four-year period and are paid in cash upon vesting. The liability fluctuates with the market value of the Partnership units and because of changes in estimated fair value determined each quarter using the Black-Scholes option valuation model. Risk free interest rates and volatility are reset at each calculation based on current rates corresponding to the remaining vesting term for each outstanding grant and ranged from 0.26% to 1.17% and 36.36% to 46.99%, respectively at March 31, 2015. The Partnership’s average distribution rate of 7.65% and historical forfeiture rate of 4.29% were used in the calculation at March 31, 2015. The Partnership recorded a reversal of expenses related to its plan to be reimbursed to its general partner of $0.1 million for the three months ended March 31, 2015 and reversal of expenses of $1.1 million for the three months ended March 31, 2014 due to the decline in the market price of the Partnership’s common units. In connection with the Long-Term Incentive Plan, payments are typically made during the first quarter of the year. Payments of $4.4 million and $5.3 million were made during the three month period ended March 31, 2015 and 2014, respectively.
	In connection with the phantom unit awards, the Compensation, Nominating and Governace Committee also granted tandem Distribution Equivalent Rights, or DERs, which entitle the holders to receive distributions equal to the distributions paid on the Partnership’s common units. The DERs are payable in cash upon vesting but may be subject to forfeiture if the grantee ceases employment prior to vesting.
	The unaccrued cost, associated with the unvested outstanding grants and related DERs at March 31, 2015 and March 31, 2014 was $6.6 million and $11.3 million, respectively.

Distributions_Paid

Distributions Paid	3 Months Ended
	Mar. 31, 2015
Equity [Abstract]
Distributions Paid	12	Distributions Paid
	On February 13, 2015, the Partnership paid a quarterly distribution of $0.35 per unit to all holders of common units on February 5, 2015.

Subsequent_Events

Subsequent Events	3 Months Ended
	Mar. 31, 2015
Subsequent Events [Abstract]
Subsequent Events	13	Subsequent Events
	The following represents material events that have occurred subsequent to March 31, 2015 through the time of the Partnership’s filing of this Quarterly Report on Form 10-Q with the Securities and Exchange Commission:
	Distributions Declared
	On April 21, 2015, the Board of Directors of GP Natural Resource Partners LLC declared a distribution of $0.09 per unit to be paid by the Partnership on May 14, 2015 to unitholders of record on May 5, 2015.
	NRP Oil and Gas Revolving Credit Facility
	In April 2015, the Partnership’s lenders completed their semi-annual redetermination of its borrowing base under the NRP Oil and Gas revolving credit facility and the $137.0 million borrowing base under that facility was redetermined to $105.0 million. In connection with this reduction, the Partnership repaid $5.0 million of outstanding borrowings under the NRP Oil and Gas revolving credit facility.
	Equity Investment
	In March 2014, Anadarko gave the Partnership written notice that it believed certain reorganization transactions conducted in 2013 within the OCI organization triggered an acceleration of the Partnership’s obligation under the purchase agreement with Anadarko to pay the additional contingent consideration in full and demanded immediate payment of such amount. The Partnership disagreed with Anadarko’s position in a written response provided to them in April 2014. In April 2015, Anadarko sent a written request for additional information regarding the OCI reorganization and indicated that they are still considering this claim against the Partnership. The Partnership does not believe the reorganization transactions triggered an obligation to pay the additional contingent consideration and will continue to engage in discussions with Anadarko to resolve the issue. However, if Anadarko were to pursue and prevail on such a claim, the Partnership would be required to pay an amount to Anadarko in excess of the amounts already paid, together with the $8.8 million accrual described above, up to the maximum amount of the additional contingent consideration, minus a deductible. Under the purchase agreement, the maximum cumulative amount of additional contingent consideration is an amount equal to the net present value of $50 million. Any additional amount paid by the Partnership would be considered to be additional acquisition consideration and added to Equity and other unconsolidated investments.

Basis_of_Presentation_Policies

Basis of Presentation (Policies)	3 Months Ended
	Mar. 31, 2015
Accounting Policies [Abstract]
Nature of Business	Nature of Business
	Natural Resource Partners L.P. (the “Partnership”) engages principally in the business of owning, operating, managing and leasing a diversified portfolio of mineral properties in the United States, including interests in coal, trona and soda ash, oil and gas, construction aggregates, frac sand and other natural resources. As used in these Notes to Consolidated Financial Statements, the terms “NRP,” “we,” “us” and “our” refer to Natural Resource Partners L.P. and its subsidiaries, unless otherwise stated or indicated by context.
Principles of Consolidation and Reporting	Principles of Consolidation and Reporting
	The accompanying unaudited Consolidated Financial Statements of the “Partnership” have been prepared in accordance with generally accepted accounting principles in the United States of America (“GAAP”) for interim financial information and with Rule 10-01 of Regulation S-X. Accordingly, they do not include all of the information and footnotes required by GAAP for complete financial statements. Certain prior period amounts have been reclassified to conform to the current period presentation. The reclassifications had no effect on the Partnership’s overall consolidated financial position, income or cash flows. In our opinion, all adjustments, consisting only of normal recurring adjustments necessary for a fair presentation, have been included. The interim financial statements should be read in conjunction with the audited financial statements and related notes included in the Partnership’s Annual Report on Form 10-K for the year ended December 31, 2014. Interim results are not necessarily indicative of the results for a full year.
	In March 2015, the Partnership recorded an out-of-period adjustment to correct an error in depletion expense related to its oil and gas royalty interests owned by BRP LLC, a joint venture with International Paper Company in which the Partnership owns a 51% interest. Depletion expense for the three months ended March 31, 2015 included a credit of $3.8 million to adjust the impact of depletion expense recorded in prior periods. After evaluating the quantitative and qualitative aspects of the error and the out-of-period adjustment to the Partnership’s financial results, management has determined that the misstatement and the out-of-period adjustment are not material to the prior period financial statements.
Recently Issued Accounting Standards	Recently Issued Accounting Standards
	In May 2014, the Financial Accounting Standards Board (“FASB”) amended its guidance on revenue recognition. The core principle of this amendment is that an entity should recognize revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. This guidance is effective for annual reporting periods beginning after December 15, 2016, including interim periods within that reporting period, with earlier adoption not permitted. This guidance can be adopted either retrospectively to each prior reporting period presented or as a cumulative-effect adjustment as of the date of adoption. We are currently evaluating the impact of the provisions of this guidance on our consolidated financial position, results of operations and cash flows.
	In April 2015, the FASB issued authoritative guidance which changes the presentation of debt issuance costs in financial statements. This guidance requires an entity to present such costs in the balance sheet as a direct deduction from the related debt liability rather than as an asset. Amortization of the costs will continue to be reported as interest expense. This guidance is effective for annual reporting periods beginning after December 15, 2016. Early adoption is permitted. This guidance will be applied retrospectively to each prior period presented. We are currently evaluating the impact of the provisions of this guidance on our consolidated balance sheets.

Acquisitions_Tables

Acquisitions (Tables)	3 Months Ended
	Mar. 31, 2015
Business Combinations [Abstract]
Business Acquisition Pro Forma Financial Information (Unaudited)	The following unaudited pro forma financial information presents a summary of the Partnership’s consolidated results of operations for the three months ended March 31, 2014, assuming the VantaCore and Sanish Field acquisitions had been completed as of January 1, 2014, including adjustments to reflect the values assigned to the net assets acquired:
		Three Months
		Ended March 31,
		2014
		(Unaudited)
		(In thousands)
	Revenue and other income except aggregates and oil and gas related revenues	$	66,876
	Aggregates related revenues		33,166
	Oil and gas related revenues		27,892
	Total revenue	$	127,934
	Net income	$	33,210
	Basic and diluted net income per common unit	$	0.3

Equity_Investment_Tables

Equity Investment (Tables)	3 Months Ended
	Mar. 31, 2015
Equity Method Investments and Joint Ventures [Abstract]
Summary of Income Allocated to NRP's Equity Interests and Amortization of Fair Value Adjustments	The income allocated to NRP’s equity interests and amortization of fair value adjustments are summarized as follows (in thousands):
		Three Months Ended
		March 31,
		2015			2014
		(Unaudited)
	Income allocation to NRP’s equity interests	$	13,727		$	11,276
	Amortization of basis difference	$	(1,204	)	$	(1,497	)
	Equity in earnings of unconsolidated investment	$	12,523		$	9,779
Schedule of Summarized Financial Information	The financial position of OCI Wyoming at March 31, 2015 and December 31, 2014 and the results of OCI Wyoming’s operations for the three months ended March 31, 2015 and 2014 are summarized as follows (in thousands):
		Three Months Ended
		March 31,
		2015			2014
		(Unaudited)
	Sales	$	120,430		$	116,240
	Gross profit	$	32,724		$	27,119
	Net income	$	28,014		$	23,012
		March 31,			December 31,
		2015			2014
		(Unaudited)
	Current assets	$	203,953		$	200,622
	Noncurrent assets	$	201,746		$	202,282
	Current liabilities	$	46,656		$	47,704
	Noncurrent liabilities	$	149,262		$	149,192

Plant_and_Equipment_Tables

Plant and Equipment (Tables)	3 Months Ended
	Mar. 31, 2015
Property, Plant and Equipment [Abstract]
Plant and Equipment	The Partnership’s plant and equipment consist of the following (in thousands):
		March 31,			December 31,
		2015			2014
		(Unaudited)
	Plant and equipment at cost	$	111,266		$	89,759
	Construction in process		141			457
	Less accumulated depreciation		(32,823	)		(30,123	)
	Total plant and equipment, net	$	78,584		$	60,093

Mineral_Rights_Tables

Mineral Rights (Tables)	3 Months Ended
	Mar. 31, 2015
Extractive Industries [Abstract]
Mineral Rights	The Partnership’s mineral rights consist of the following (in thousands):
		March 31,			December 31,
		2015			2014
		(Unaudited)
	Coal	$	1,541,343		$	1,541,572
	Oil and Gas		570,195			560,395
	Aggregates		212,690			211,490
	Other		15,014			15,014
	Less accumulated depletion and amortization		(565,793	)		(546,619	)
	Total mineral rights, net	$	1,773,449		$	1,781,852

Intangible_Assets_Tables

Intangible Assets (Tables)	3 Months Ended
	Mar. 31, 2015
Goodwill and Intangible Assets Disclosure [Abstract]
Intangible Assets	Amounts recorded as intangible assets along with the balances and accumulated amortization are reflected in the table below (in thousands):
		March 31,			December 31,
		2015			2014
		(Unaudited)
	Contract intangibles	$	82,972		$	82,972
	Other intangibles		3,004			3,004
	Less accumulated amortization		(26,263	)		(25,243	)
	Total intangible assets, net	$	59,713		$	60,733

Debt_and_DebtAffiliate_Tables

Debt and Debt-Affiliate (Tables)	3 Months Ended
	Mar. 31, 2015
Debt Disclosure [Abstract]
Debt	As of March 31, 2015 and December 31, 2014, debt and debt—affiliate consisted of the following (in thousands):
		March 31,			December 31,
		2015			2014
		(Unaudited)
	NRP LP Debt:
	$425 million 9.125% senior notes, with semi-annual interest payments in April and October, maturing October 2018, $300 million issued at 99.007% and $125 million issued at 99.5%	$	422,356		$	422,167
	Opco Debt:
	$300 million floating rate revolving credit facility, due August 2016		225,000			200,000
	$200 million floating rate term loan, due January 2016		75,000			75,000
	4.91% senior notes, with semi-annual interest payments in June and December, with annual principal payments in June, maturing in June 2018		18,467			18,467
	8.38% senior notes, with semi-annual interest payments in March and September, with annual principal payments in March, maturing in March 2019		85,714			107,143
	5.05% senior notes, with semi-annual interest payments in January and July, with annual principal payments in July, maturing in July 2020		46,154			46,154
	5.31% utility local improvement obligation, with annual principal and interest payments, maturing in March 2021		1,153			1,345
	5.55% senior notes, with semi-annual interest payments in June and December, with annual principal payments in June, maturing in June 2023		24,300			24,300
	4.73% senior notes, with semi-annual interest payments in June and December, with annual principal payments in December, maturing in December 2023		67,500			67,500
	5.82% senior notes, with semi-annual interest payments in March and September, with annual principal payments in March, maturing in March 2024		135,000			150,000
	8.92% senior notes, with semi-annual interest payments in March and September, with annual principal payments in March, maturing in March 2024		40,910			45,455
	5.03% senior notes, with semi-annual interest payments in June and December, with annual principal payments in December, maturing in December 2026		161,538			161,538
	5.18% senior notes, with semi-annual interest payments in June and December, with annual principal payments in December, maturing in December 2026		46,154			46,154
	NRP Oil and Gas Debt:
	Reserve-based revolving credit facility due 2019		110,000			110,000
	Total debt and debt – affiliate		1,459,246			1,475,223
	Less: current portion of long-term debt		(155,983	)		(80,983	)
	Total long-term debt and debt – affiliate	$	1,303,263		$	1,394,240

Fair_Value_Measurements_Tables

Fair Value Measurements (Tables)	3 Months Ended
	Mar. 31, 2015
Fair Value Disclosures [Abstract]
Schedule of Carrying Amount and Estimated Fair Value of Other Financial Instruments	The following table (in thousands) shows the carrying amount and estimated fair value of our other financial instruments:
			March 31, 2015				December 31, 2014
			Carrying		Estimated		Carrying		Estimated
			Amount		Fair Value		Amount		Fair Value
			(Unaudited)
	Assets
	Contracts receivable – affiliate, current and long-term(3)		$	4,646	$	5,041	$	4,870	$	5,162
	Debt and debt – affiliate
	NRP LP senior notes(1)		$	422,356	$	416,957	$	422,167	$	423,780
	Opco revolving credit facility and term loan facility(2)		$	300,000	$	300,000	$	275,000	$	275,000
	Opco senior notes and utility local improvement obligation(3)		$	626,890	$	629,521	$	668,056	$	672,740
	NRP Oil and Gas revolving credit facility(2)		$	110,000	$	110,000	$	110,000	$	110,000
	(1)	The Level 2 estimated fair value was based upon quotations obtained for similar instruments on the closing trading prices near quarter end.
	(2)	The Level 3 estimated fair value approximates the carrying amount because the interest rates are variable and reflective of market rates and the Partnership has the ability to repay this debt at any time without penalty.
	(3)	The Level 3 estimated fair value was based on comparable term risk-free treasury issues with a market rate component determined by current financial instruments with similar characteristics.

Related_Party_Transactions_Tab

Related Party Transactions (Tables)	3 Months Ended
	Mar. 31, 2015
Related Party Transactions [Abstract]
Summary of Reimbursements	The reimbursements to affiliates of the Partnership’s general partner for services performed by Western Pocahontas Properties and Quintana Minerals Corporation are as follows (in thousands):
		Three Months Ended
		March 31,
		2015		2014
		(Unaudited)
	General and administrative—affiliate	$	3,786	$	3,094

Major_Lessees_Tables

Major Lessees (Tables)	3 Months Ended
	Mar. 31, 2015
Risks and Uncertainties [Abstract]
Revenues from Lessees that Exceeded Ten Percent of Total Revenues and Other Income	Revenues from lessees that exceeded ten percent of total revenues and other income for the periods are presented below (in thousands except for percentages):
		Three Months Ended
		March 31,
		2015					2014
		(Unaudited)
		Revenues		Percent			Revenues		Percent
	Foresight Energy and affiliates	$	18,298		17	%	$	17,882		22	%
	Alpha Natural Resources	$	8,829		8	%	$	11,642		14	%

LongTerm_Incentive_Plans_Table

Long-Term Incentive Plans (Tables)	3 Months Ended
	Mar. 31, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Summary of Activity in Outstanding Grants	A summary of activity in the outstanding grants during 2015 is as follows:
		(Unaudited)
	Outstanding grants at January 1, 2015		1,153,393
	Grants during the year		468,486
	Grants vested and paid during the year		(290,430	)
	Forfeitures during the year		—
	Outstanding grants at March 31, 2015		1,331,449

Basis_of_Presentation_Addition

Basis of Presentation - Additional Information (Detail) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015
Corporate Joint Venture [Member]
Collaborative Arrangements Non collaborative Arrangements And Business Acquisitions Transactions [Line Items]
Ownership percentage in joint venture	51.00%
Restatement Adjustment [Member]
Collaborative Arrangements Non collaborative Arrangements And Business Acquisitions Transactions [Line Items]
Depletion expenses	3.8

Acquisitions_Additional_Inform

Acquisitions - Additional Information (Detail) (USD $)	3 Months Ended	0 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Oct. 01, 2014	Nov. 12, 2014
			acre
			Wells
Business Acquisition [Line Items]
Increase in plant and equipment acquired	$22.50
VantaCore Partners LLC [Member]
Business Acquisition [Line Items]
Aggregate acquisition cost		201.1
Number of hard rock quarries		3
Number of sand and gravel plants		5
Number of asphalt plants		2
Sanish Field [Member]
Business Acquisition [Line Items]
Aggregate acquisition cost			$339.10
Land acquired			6,086
Number of Oil & Gas wells			196

Acquisitions_Business_Acquisit

Acquisitions - Business Acquisition Pro Forma Financial Information (Unaudited) (Detail) (USD $)	3 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Mar. 31, 2014
Business Combinations [Abstract]
Revenue and other income except aggregates and oil and gas related revenues	$66,876
Aggregates related revenues	33,166
Oil and gas related revenues	27,892
Total revenue	127,934
Net income	$33,210
Basic and diluted net income per common unit	$0.30

Equity_Investment_Additional_I

Equity Investment - Additional Information (Detail) (USD $)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Schedule of Equity Method Investments [Line Items]
Distributions from Equity Method Investment	$10,903,000	$11,645,000
OCI Wyoming [Member]
Schedule of Equity Method Investments [Line Items]
Distributions from Equity Method Investment	10,900,000	11,600,000
Percentage of partnership interest owned	49.00%
Weighted average useful life of assets	28 years
Contingent consideration accrued	8,800,000
Contingent consideration paid		500,000
Difference between carried amount of investment and underlying equity	160,500,000		162,700,000
OCI Wyoming [Member] | Anadarko Holding Company [Member]
Schedule of Equity Method Investments [Line Items]
Contingent consideration paid	$3,800,000

Equity_Investment_Summary_of_I

Equity Investment - Summary of Income Allocated to NRP's Equity Interests and Amortization of Fair Value Adjustments (Detail) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Schedule of Equity Method Investments [Line Items]
Equity in earnings of unconsolidated investment	$12,523	$9,779
OCI Wyoming [Member]
Schedule of Equity Method Investments [Line Items]
Income allocation to NRP's equity interests	13,727	11,276
Amortization of basis difference	-1,204	-1,497
Equity in earnings of unconsolidated investment	$12,523	$9,779

Equity_Investment_Schedule_of_

Equity Investment - Schedule of Summarized Financial Information (Detail) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Schedule of Equity Method Investments [Line Items]
Net income	$17,489	$32,605
Current assets	101,393		136,118
Current liabilities	224,553		147,931
OCI Wyoming [Member]
Schedule of Equity Method Investments [Line Items]
Sales	120,430	116,240
Gross profit	32,724	27,119
Net income	28,014	23,012
Current assets	203,953		200,622
Noncurrent assets	201,746		202,282
Current liabilities	46,656		47,704
Noncurrent liabilities	$149,262		$149,192

Plant_and_Equipment_Plant_and_

Plant and Equipment - Plant and Equipment (Detail) (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Thousands, unless otherwise specified
Property, Plant and Equipment [Abstract]
Plant and equipment at cost	$111,266	$89,759
Construction in process	141	457
Less accumulated depreciation	-32,823	-30,123
Total plant and equipment, net	$78,584	$60,093

Plant_and_Equipment_Additional

Plant and Equipment - Additional Information (Detail) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Property, Plant and Equipment [Abstract]
Total depreciation and amortization expense on plant and equipment	$4.50	$1.30

Mineral_Rights_Mineral_Rights_

Mineral Rights - Mineral Rights (Detail) (USD $)	Mar. 31, 2015	Dec. 31, 2014	Dec. 01, 2014
In Thousands, unless otherwise specified
Costs Incurred, Oil and Gas Property Acquisition, Exploration, and Development Activities [Line Items]
Less accumulated depletion and amortization	($565,793)		($546,619)
Total mineral rights, net	1,773,449	1,781,852	1,781,852
Coal [Member]
Costs Incurred, Oil and Gas Property Acquisition, Exploration, and Development Activities [Line Items]
Partnership's mineral rights	1,541,343		1,541,572
Oil And Gas [Member]
Costs Incurred, Oil and Gas Property Acquisition, Exploration, and Development Activities [Line Items]
Partnership's mineral rights	570,195		560,395
Aggregate [Member]
Costs Incurred, Oil and Gas Property Acquisition, Exploration, and Development Activities [Line Items]
Partnership's mineral rights	212,690		211,490
Other [Member]
Costs Incurred, Oil and Gas Property Acquisition, Exploration, and Development Activities [Line Items]
Partnership's mineral rights	$15,014		$15,014

Mineral_Rights_Additional_Info

Mineral Rights - Additional Information (Detail) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Extractive Industries [Abstract]
Total depletion and amortization expense on mineral rights	$19.90	$12.50

Intangible_Assets_Intangible_A

Intangible Assets - Intangible Assets (Detail) (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Thousands, unless otherwise specified
Goodwill and Intangible Assets Disclosure [Abstract]
Contract intangibles	$82,972	$82,972
Other intangibles	3,004	3,004
Less accumulated amortization	-26,263	-25,243
Total intangible assets, net	$59,713	$60,733

Intangible_Assets_Additional_I

Intangible Assets - Additional Information (Detail) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Goodwill and Intangible Assets Disclosure [Abstract]
Total amortization expense on intangible assets	$1	$0.80

Debt_and_DebtAffiliate_Additio

Debt and Debt-Affiliate - Additional Information (Detail) (USD $)	3 Months Ended				12 Months Ended	1 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014	Sep. 30, 2013	Dec. 31, 2013	Sep. 30, 2013	Aug. 31, 2013	Oct. 31, 2014
Debt Instrument [Line Items]
Floating rate revolving credit facility	$1,459,246,000		$1,475,223,000
Term Loan	41,166,000	41,166,000
Term Loan [Member]
Debt Instrument [Line Items]
Repayment of principal amount			24,000,000	101,000,000
Weighted average interest rate for the debt outstanding	2.19%	2.25%
Amount received from debt issuance					200,000,000
Borrowings outstanding	75,000,000
NRP LP [Member]
Debt Instrument [Line Items]
Rate of senior notes	9.13%			9.13%		9.13%		9.13%
Floating rate revolving credit facility				300,000,000		300,000,000		125,000,000
Senior Note issue percentage				99.01%		99.01%		99.50%
Repayment of principal amount						289,000,000
Proceeds from issuance of cost						122,600,000
NRP LP [Member] | Maximum [Member]
Debt Instrument [Line Items]
Fixed charge coverage ratio	2
NRP LP [Member] | Minimum [Member]
Debt Instrument [Line Items]
Fixed charge coverage ratio	1
Opco [Member]
Debt Instrument [Line Items]
Term Loan						91,000,000
Principal payments on its senior notes	41,000,000	41,000,000
Ratio of consolidated indebtedness to consolidated EBITDDA	4
Percentage of consolidated net tangible assets debt of subsidiaries not permitted to exceed	10.00%
Ratio of consolidated EBITDDA to consolidated fixed charges	3.5
Additional interest accrue	2.00%
Partnership leverage ratio	3.75
Opco [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Ratio of consolidated indebtedness to consolidated EBITDDA	4
Ratio of consolidated EBITDDA to consolidated fixed charges	3.5
Maximum increase in aggregate commitment	500,000,000
Weighted average interest rate	1.94%	1.98%
Opco [Member] | $300 million floating rate revolving credit facility, due August 2016 [Member]
Debt Instrument [Line Items]
Floating rate revolving credit facility	225,000,000		200,000,000
Floating rate revolving credit facility	300,000,000
Opco [Member] | $300 million floating rate revolving credit facility, due August 2016 [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Commitment fee on the undrawn portion of the revolving credit facility rates	0.18% to 0.40%
Opco [Member] | Term Loan [Member]
Debt Instrument [Line Items]
Leverage ratio, maximum	4
Minimum interest coverage ratio	3.5
Opco [Member] | Maximum [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Commitment fee on the unused portion of the borrowing base under the credit facility		0.40%
Opco [Member] | Minimum [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Commitment fee on the unused portion of the borrowing base under the credit facility	0.18%
NRP Oil and Gas [Member]
Debt Instrument [Line Items]
Commitment fee on the undrawn portion of the revolving credit facility rates	0.375% to 0.50%
Leverage ratio, maximum	3.5
Debt Instrument, Interest Rate Terms	The higher of (i) the prime rate as announced by the agent bank; (ii) the federal funds rate plus 0.50%; or (iii) LIBOR plus 1%, in each case plus an applicable margin ranging from 0.50% to 1.50%; or a rate equal to LIBOR, plus an applicable margin ranging from 1.50% to 2.50%.
Current ratio, minimum	1
NRP Oil and Gas [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Maximum increase in aggregate commitment	137,000,000
Weighted average interest rate for the debt outstanding	2.43%	1.91%
Borrowings outstanding	110,000,000		110,000,000
Term of credit facility							5 years
Senior secured revolving credit facility							100,000,000
Revolving credit facility maturity date	12-Nov-19
Floating rate revolving credit facility	137,000,000
NRP Oil and Gas [Member] | Amended On November 2014 [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Maximum increase in aggregate commitment	$500,000,000
NRP Oil and Gas [Member] | Maximum [Member]
Debt Instrument [Line Items]
Commitment fee on the unused portion of the borrowing base under the credit facility	0.50%
NRP Oil and Gas [Member] | Minimum [Member]
Debt Instrument [Line Items]
Commitment fee on the unused portion of the borrowing base under the credit facility	0.38%

Debt_and_DebtAffiliatet_Debt_D

Debt and Debt-Affiliatet - Debt (Detail) (USD $)	Mar. 31, 2015	Dec. 31, 2014	Oct. 31, 2014	Sep. 30, 2013
In Thousands, unless otherwise specified
Debt Instrument [Line Items]
Total debt	$1,459,246	$1,475,223
Less: current portion of long term debt	-155,983	-80,983
Total long-term debt and debt - affiliate	1,283,352	1,374,336
NRP LP [Member]
Debt Instrument [Line Items]
Total debt			125,000	300,000
NRP LP [Member] | 9.125% senior notes, with semi-annual interest payments in April and October, maturing October 2018 [Member]
Debt Instrument [Line Items]
Total debt	422,356	422,167
Opco [Member] | $300 million floating rate revolving credit facility, due August 2016 [Member]
Debt Instrument [Line Items]
Total debt	225,000	200,000
Opco [Member] | $200 million floating rate term loan, due January 2016 [Member]
Debt Instrument [Line Items]
Total debt	75,000	75,000
Opco [Member] | 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]
Total debt	18,467	18,467
Opco [Member] | 8.38% senior notes, with semi-annual interest payments in March and September, with annual principal payments in March, maturing in March 2019 [Member]
Debt Instrument [Line Items]
Total debt	85,714	107,143
Opco [Member] | 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]
Total debt	46,154	46,154
Opco [Member] | 5.31% utility local improvement obligation, with annual principal and interest payments, maturing in March 2021 [Member]
Debt Instrument [Line Items]
Total debt	1,153	1,345
Opco [Member] | 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]
Total debt	24,300	24,300
Opco [Member] | 4.73% senior notes, with semi-annual interest payments in June and December, with annual principal payments in December, maturing in December 2023 [Member]
Debt Instrument [Line Items]
Total debt	67,500	67,500
Opco [Member] | 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]
Total debt	135,000	150,000
Opco [Member] | 8.92% 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]
Total debt	40,910	45,455
Opco [Member] | 5.03% senior notes, with semi-annual interest payments in June and December, with annual principal payments in December, maturing in December 2026 [Member]
Debt Instrument [Line Items]
Total debt	161,538	161,538
Opco [Member] | 5.18% senior notes, with semi-annual interest payments in June and December, with annual principal payments in December, maturing in December 2026 [Member]
Debt Instrument [Line Items]
Total debt	46,154	46,154
NRP Oil and Gas [Member] | Reserve Based Revolving Credit Facility Due 2019 [Member]
Debt Instrument [Line Items]
Total debt	$110,000	$110,000

Debt_and_DebtAffiliatet_Debt_P

Debt and Debt-Affiliatet - Debt (Parenthetical) (Detail) (USD $)	Mar. 31, 2015	Oct. 31, 2014	Sep. 30, 2013
In Millions, unless otherwise specified
NRP LP [Member]
Debt Instrument [Line Items]
Rate of senior notes	9.13%	9.13%	9.13%
Senior Note issue percentage		99.50%	99.01%
9.125% senior notes, with semi-annual interest payments in April and October, maturing October 2018 [Member] | NRP LP [Member]
Debt Instrument [Line Items]
Senior Notes, Face amount	425
Rate of senior notes	9.13%
9.125% senior notes, with semi-annual interest payments in April and October, maturing October 2018 [Member] | Senior Notes issued at 99.007% [Member] | NRP LP [Member]
Debt Instrument [Line Items]
Floating rate revolving credit facility	300
Senior Note issue percentage	99.01%
9.125% senior notes, with semi-annual interest payments in April and October, maturing October 2018 [Member] | Senior Notes issued at 99.5% [Member] | NRP LP [Member]
Debt Instrument [Line Items]
Floating rate revolving credit facility	125
Senior Note issue percentage	99.50%
$300 million floating rate revolving credit facility, due August 2016 [Member] | Opco [Member]
Debt Instrument [Line Items]
Floating rate revolving credit facility	300
$200 million floating rate term loan, due January 2016 [Member] | Opco [Member]
Debt Instrument [Line Items]
Floating rate revolving credit facility	200
4.91% senior notes, with semi-annual interest payments in June and December, with annual principal payments in June, maturing in June 2018 [Member] | Opco [Member]
Debt Instrument [Line Items]
Rate of senior notes	4.91%
8.38% senior notes, with semi-annual interest payments in March and September, with annual principal payments in March, maturing in March 2019 [Member] | Opco [Member]
Debt Instrument [Line Items]
Rate of senior notes	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] | Opco [Member]
Debt Instrument [Line Items]
Rate of senior notes	5.05%
5.31% utility local improvement obligation, with annual principal and interest payments, maturing in March 2021 [Member] | Opco [Member]
Debt Instrument [Line Items]
Rate of senior notes	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] | Opco [Member]
Debt Instrument [Line Items]
Rate of senior notes	5.55%
4.73% senior notes, with semi-annual interest payments in June and December, with annual principal payments in December, maturing in December 2023 [Member] | Opco [Member]
Debt Instrument [Line Items]
Rate of senior notes	4.73%
5.82% senior notes, with semi-annual interest payments in March and September, with annual principal payments in March, maturing in March 2024 [Member] | Opco [Member]
Debt Instrument [Line Items]
Rate of senior notes	5.82%
8.92% senior notes, with semi-annual interest payments in March and September, with annual principal payments in March, maturing in March 2024 [Member] | Opco [Member]
Debt Instrument [Line Items]
Rate of senior notes	8.92%
5.03% senior notes, with semi-annual interest payments in June and December, with annual principal payments in December, maturing in December 2026 [Member] | Opco [Member]
Debt Instrument [Line Items]
Rate of senior notes	5.03%
5.18% senior notes, with semi-annual interest payments in June and December, with annual principal payments in December, maturing in December 2026 [Member] | Opco [Member]
Debt Instrument [Line Items]
Rate of senior notes	5.18%

Fair_Value_Measurements_Schedu

Fair Value Measurements - Schedule of Carrying Amount and Estimated Fair Value of Other Financial Instruments (Detail) (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Thousands, unless otherwise specified
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Carrying Amount	$4,646	$4,870
Estimated Fair Value	5,041	5,162
NRP LP Senior Notes [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Carrying Amount	422,356	422,167
Estimated Fair Value	416,957	423,780
Opco Revolving Credit Facility And Term Loan Facility [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Carrying Amount	300,000	275,000
Estimated Fair Value	300,000	275,000
Opco Senior Notes and Utility Local Improvement Obligation [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Carrying Amount	626,890	668,056
Estimated Fair Value	629,521	672,740
NRP Oil And Gas Revolving Credit Facility [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Carrying Amount	110,000	110,000
Estimated Fair Value	$110,000	$110,000

Related_Party_Transactions_Add

Related Party Transactions - Additional Information (Detail) (USD $)	3 Months Ended		1 Months Ended	12 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Oct. 31, 2014	Dec. 31, 2014
Related Party Transaction [Line Items]
Accounts payable - affiliates	$936,000			$950,000
Lease expenses	200,000
Total revenues and other income	109,677,000	80,309,000
Unrecouped minimum royalty payments	86,315,000			87,053,000
Accounts receivable - affiliates	5,851,000			9,494,000
Senior Notes Due 2018 [Member] | Cline Trust Company, LLC [Member]
Related Party Transaction [Line Items]
Partnership common units owned			5,350,000
Principal amount of partnership purchased			20,000,000
Rate of senior notes			9.13%
Aggregate principal amount of senior notes			125,000,000
Senior notes due	19,900,000
Quintana Minerals [Member]
Related Party Transaction [Line Items]
Accounts payable - affiliates	600,000			600,000
Western Pocahontas Properties [Member]
Related Party Transaction [Line Items]
Accounts payable - affiliates	300,000			400,000
Cline Affiliates [Member]
Related Party Transaction [Line Items]
Rate of interest in the partnerships general partner	31.00%
Related party transaction number of units hold by the related party in partnerships' general partner	4,900,000
Unrecouped minimum royalty payments	86,100,000
Accounts receivable-affiliates	5,600,000			9,200,000
Net amount receivable	4,600,000			5,600,000
Accounts receivable - affiliates	200,000			1,100,000
Cline Affiliates [Member] | Coal Sales [Member]
Related Party Transaction [Line Items]
Total revenues and other income	18,300,000	17,900,000
Sugar Camp [Member]
Related Party Transaction [Line Items]
Aggregate payments remaining under the lease	85,000,000			86,300,000
Unearned income	38,100,000			39,000,000
Net amount receivable	46,900,000			47,300,000
Accounts receivable - affiliates	1,800,000			1,800,000
Corsa [Member]
Related Party Transaction [Line Items]
Unrecouped minimum royalty payments	200,000
Accounts receivable - affiliates	200,000			300,000
Coal royalty revenues	$800,000			$900,000

Related_Party_Transactions_Sum

Related Party Transactions - Summary of Reimbursements (Detail) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Related Party Transactions [Abstract]
Reimbursement for services	$3,786	$3,094

Major_Lessees_Revenues_from_Le

Major Lessees - Revenues from Lessees that Exceeded Ten Percent of Total Revenues and Other Income (Detail) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Foresight Energy and Affiliates [Member]
Operating Leased Assets [Line Items]
Revenues	$18,298	$17,882
Percent	17.00%	22.00%
Alpha Natural Resources [Member]
Operating Leased Assets [Line Items]
Revenues	$8,829	$11,642
Percent	8.00%	14.00%

Major_Lessees_Additional_Infor

Major Lessees - Additional Information (Detail)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Operating Leased Assets [Line Items]
Minimum Percentage of revenues and other income derived from major two leases	25.00%
Williamson [Member]
Operating Leased Assets [Line Items]
Percentage of revenues and other income received from major lessee excluding reserve swap	5.00%	11.00%

LongTerm_Incentive_Plans_Summa

Long-Term Incentive Plans - Summary of Activity in Outstanding Grants (Detail)	3 Months Ended
	Mar. 31, 2015
Compensation and Retirement Disclosure [Abstract]
Outstanding grants at the beginning of the period	1,153,393
Grants during the period	468,486
Grants vested and paid during the period	-290,430
Forfeitures during the period	0
Outstanding grants at the end of the period	1,331,449

LongTerm_Incentive_Plans_Addit

Long-Term Incentive Plans - Additional Information (Detail) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period of Grants in years	4 years
Risk free interest rate	0.26%
Risk free interest rate	1.17%
Volatility rate	36.36%
Volatility rate	46.99%
Partnership's historical distribution rate	7.65%
Partnership's historical forfeiture rate	4.29%
Expenses related to Incentive Plan to be reimbursed to general partner	$4.40	$5.30
Unaccrued cost associated with outstanding grants and related DERs	6.6	11.3
General Partner [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Payments made in connection with Long-Term Incentive Plan	$0.10	$1.10

Distributions_Additional_Infor

Distributions - Additional Information (Detail) (USD $)	0 Months Ended
	Feb. 13, 2015
Equity [Abstract]
Quarterly distribution to holders of common units	$0.35

Subsequent_Events_Additional_I

Subsequent Events - Additional Information (Detail) (USD $)	0 Months Ended	1 Months Ended	3 Months Ended	0 Months Ended	1 Months Ended
In Millions, except Per Share data, unless otherwise specified	Feb. 13, 2015	Sep. 30, 2013	Mar. 31, 2015	Apr. 21, 2015	Apr. 30, 2015
Subsequent Event [Line Items]
Distributions per unit declared	$0.35
NRP LP [Member]
Subsequent Event [Line Items]
Repayment of outstanding borrowings		$289
OCI Wyoming [Member]
Subsequent Event [Line Items]
Cash distributions from equity investment			0
Subsequent Event [Member]
Subsequent Event [Line Items]
Distributions per unit declared				$0.09
Subsequent Event [Member] | NRP LP [Member]
Subsequent Event [Line Items]
Repayment of outstanding borrowings					5
Subsequent Event [Member] | Anadarko Holding Company [Member]
Subsequent Event [Line Items]
Contingent consideration recorded as accrued liabilites					8.8
Net present value payable of contingent consideration under the agreement					50
Subsequent Event [Member] | NRP Oil And Gas Revolving Credit Facility [Member]
Subsequent Event [Line Items]
Line of credit facility maximum borrowing capacity					137
Line of credit facility current borrowing capacity					$105