Natural Resource Partners (NRP) 10-Q 7 Aug 15 2015 Q2 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	6 Months Ended
	Jun. 30, 2015	Aug. 07, 2015
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Jun. 30, 2015
Document Fiscal Year Focus	2,015
Document Fiscal Period Focus	Q2
Trading Symbol	NRP
Entity Registrant Name	NATURAL RESOURCE PARTNERS LP
Entity Central Index Key	1,171,486
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		122,299,825

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Current assets:
Cash and cash equivalents	$ 27,525	$ 50,076
Accounts receivable, net	54,230	66,455
Accounts receivable-affiliate	8,192	9,494
Inventory	7,126	5,814
Prepaid expenses and other	2,854	4,279
Total current assets	99,927	136,118
Land	25,243	25,243
Plant and equipment, net	77,287	60,093
Mineral rights, net	1,788,454	1,781,852
Intangible assets, net	59,182	60,733
Equity in unconsolidated investment	263,619	264,020
Long-term contracts receivable-affiliate	49,236	50,008
Goodwill	4,840	52,012
Other assets	17,317	14,645
Total assets	2,385,105	2,444,724
Current liabilities:
Accounts payable	16,692	22,465
Accounts payable-affiliates	939	950
Accrued liabilities	45,924	43,533
Current portion of long-term debt, net	155,983	80,983
Total current liabilities	219,538	147,931
Deferred revenue	80,706	73,207
Deferred revenue-affiliates	87,116	87,053
Long-term debt, net	1,256,218	1,374,336
Long-term debt, net-affiliate	19,917	19,904
Other non-current liabilities	$ 9,797	$ 22,138
Commitments and contingencies (see Note 13)
Partners' Capital:
Common unitholders' interest (122,299,825 units outstanding)	$ 703,055	$ 709,019
General partner's interest	12,122	12,245
Accumulated other comprehensive loss	(1,214)	(459)
Total partners' capital	713,963	720,805
Non-controlling interest	(2,150)	(650)
Total capital	711,813	720,155
Total liabilities and capital	$ 2,385,105	$ 2,444,724

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - shares	Jun. 30, 2015	Dec. 31, 2014
Statement of Financial Position [Abstract]
Common units outstanding	122,299,825	122,299,825

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Revenues and other income:
Coal related revenues	$ 28,562	$ 34,271	$ 58,983	$ 67,917
Coal related revenues-affiliates	32,342	21,090	51,403	39,817
Aggregates related revenues	42,886	3,563	71,832	6,959
Oil and gas related revenues	14,839	17,822	30,069	27,880
Equity in earnings of unconsolidated investment	11,599	9,401	24,122	19,180
Property taxes	3,070	3,378	6,074	7,345
Other	4,332	1,036	4,824	1,772
Total revenues and other income	137,630	90,561	247,307	170,870
Costs and expenses:
Coal related expenses	504	663	1,825	1,240
Coal related expenses-affiliates	109		109
Aggregates related expenses	32,800		55,207	73
Oil and gas related expenses	2,999	2,291	6,760	4,212
General and administrative	2,234	6,029	9,689	8,719
General and administrative-affiliates	3,535	3,000	7,321	6,094
Depreciation, depletion and amortization	30,660	16,350	56,052	30,997
Asset impairments	3,803	5,624	3,803	5,624
Property, franchise and other taxes	5,066	6,201	10,204	11,069
Total operating expenses	81,710	40,158	150,970	68,028
Income from operations	55,920	50,403	96,337	102,842
Other income (expense)
Interest expense	(23,343)	(19,037)	(46,286)	(38,897)
Interest income	1	41	16	67
Other expense, net	(23,342)	(18,996)	(46,270)	(38,830)
Net income	32,578	31,407	50,067	64,012
Less: net income attributable to non-controlling interest	(1,244)		(1,244)
Net income attributable to NRP	31,334	31,407	48,823	64,012
Net income attributable to partners:
Limited partners	30,707	30,779	47,847	62,732
General partner	$ 627	$ 628	$ 976	$ 1,280
Basic and diluted net income per common unit	$ 0.25	$ 0.28	$ 0.39	$ 0.57
Weighted average number of common units outstanding	122,300	110,403	122,300	110,127
Net income	$ 32,578	$ 31,407	$ 50,067	$ 64,012
Comprehensive (income) loss from unconsolidated investment and other	210	(164)	(755)	(264)
Comprehensive income attributable to non-controlling interest	(1,244)		(1,244)
Comprehensive income attributable to NRP	$ 31,544	$ 31,243	$ 48,068	$ 63,748

Consolidated Statements of Cash

Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014
Cash flows from operating activities:
Net income	$ 50,067	$ 64,012
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation, depletion and amortization	56,052	30,997
Asset impairment	3,803	5,624
Gain on reserve swap	(9,290)
Equity earnings from unconsolidated investment	(24,122)	(19,180)
Distributions from equity earnings from unconsolidated investment	21,805	21,935
Other, net	(2,728)	1,468
Other, net-affiliates	13
Change in operating assets and liabilities:
Accounts receivable	12,560	(2,678)
Accounts receivable-affiliate	1,302	(1,352)
Accounts payable	581	(1,120)
Accounts payable-affiliates	(11)	54
Accrued liabilities	(5,419)	(1,968)
Deferred revenue	7,499	(1,165)
Deferred revenue-affiliates	63	8,264
Accrued incentive plan expenses	(6,952)	(5,916)
Other items, net	1,252	318
Other items, net-affiliates	(365)	345
Net cash provided by operating activities	106,110	99,638
Cash flows from investing activities:
Acquisition of mineral rights	(29,121)	(8,891)
Acquisition of plant and equipment and other	(5,073)	(135)
Proceeds from sale of mineral rights	5,281
Proceeds from sale of plant and equipment and other	5,255
Return on equity and other unconsolidated investments		3,633
Return on direct financing lease and contractual override-affiliate	1,137	600
Net cash used in investing activities	(22,521)	(4,793)
Cash flows from financing activities:
Proceeds from loans	25,000	2,000
Repayment of loans	(68,483)	(53,483)
Proceeds from issuance of common units		13,842
Capital contribution by general partner		347
Distributions to non-controlling interest	(2,744)	(974)
Distributions to partners	(54,910)	(78,639)
Debt issuance costs and other	(5,003)	(438)
Net cash used in financing activities	(106,140)	(117,345)
Net decrease in cash and cash equivalents	(22,551)	(22,500)
Cash and cash equivalents at beginning of period	50,076	92,513
Cash and cash equivalents at end of period	27,525	70,013
Supplemental cash flow information:
Cash paid during the period for interest	44,174	$ 39,135
Plant, equipment and mineral rights funded with accounts payable or accrued liabilities	$ 4,452

Consolidated Statements of Part

Consolidated Statements of Partners' Capital (Unaudited) - 6 months ended Jun. 30, 2015 - USD ($) shares in Thousands, $ in Thousands	Total	General Partner [Member]	Common Stock [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Partners' Capital Excluding Non-Controlling Interest [Member]	Non-Controlling Interest [Member]
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	(54,910)	(1,099)	$ (53,811)		(54,910)
Distributions to non-controlling interest	(2,744)					(2,744)
Net income	48,823	976	47,847		48,823	1,244
Comprehensive loss from unconsolidated investment and other	(755)			(755)	(755)
Balance at Jun. 30, 2015	$ 713,963	$ 12,122	$ 703,055	$ (1,214)	$ 713,963	$ (2,150)
Balance, units at Jun. 30, 2015			122,300

Basis of Presentation

Basis of Presentation	6 Months Ended
	Jun. 30, 2015
Organization, Consolidation and Presentation of Financial Statements [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 six months ended June 30, 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, 2017, 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	6 Months Ended
	Jun. 30, 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 $200.6 million in cash and common units. Headquartered in Philadelphia, Pennsylvania, VantaCore operates four 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 as a business combination 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 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. In the second 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 VantaCore’s right to mine and intangible assets that existed as of the acquisition date. As a result of this adjustment, Mineral rights, net and Intangible assets, net were increased by $24.7 million with a corresponding decrease to Goodwill. Measurement-period adjustments were not material to prior period financial statements and were recorded during the period in which the amount of the adjustment was determined. The accounting for the VantaCore acquisition was completed in the second quarter of 2015 and is summarized as follows: VantaCore Purchase Price Allocation October 1, 2014 (In thousands) Consideration Cash $ 168,978 NRP common units 31,604 Total consideration given $ 200,582 Allocation of Purchase Price Current assets $ 37,222 Land, property and equipment 62,911 Mineral rights 111,500 Other assets 4,347 Current liabilities (16,953 ) Asset retirement obligation (3,285 ) Goodwill 4,840 Fair value of net assets acquired $ 200,582 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 as a business combination 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 results of operations of the acquisition have been included in our consolidated financial statements since the acquisition date. The accounting for the Sanish Field acquisition was completed in the second quarter of 2015 without significant changes during the measurement period and is summarized as follows: Sanish Field Purchase Price Allocation November 12, 2014 (In thousands) Consideration Cash $ 339,093 Allocation of Purchase Price Mineral rights - proven oil and gas properties 298,293 Mineral rights - probable and possible oil and gas resources 40,800 Fair value of net assets acquired $ 339,093 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 and six months ended June 30, 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 June 30, 2014 Six Months Ended June 30, 2014 (Unaudited) (In thousands) Revenues and other income except aggregates related and oil and gas related revenues $ 69,213 $ 136,088 Aggregates related revenues 49,094 82,261 Oil and gas related revenues 34,636 62,528 Total revenues and other income $ 152,943 $ 280,877 Net income $ 36,752 $ 69,524 Basic and diluted net income per common unit $ 0.33 $ 0.62

Equity Investment

Equity Investment	6 Months Ended
	Jun. 30, 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. OCI Wyoming distributed $10.9 million and $13.9 million to us in the three months ended June 30, 2015 and 2014, respectively, and OCI Wyoming distributed $21.8 million and $25.6 million to us in the six months ended June 30, 2015 and 2014, respectively. 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 $157.6 million and $162.7 million as of June 30, 2015 and December 31, 2014, respectively. This excess basis relates to plant, property and equipment and right to mine assets. The excess basis difference that relates to property, plant and equipment is being amortized into income using the straight-line method over a weighted average of 28 years. The excess basis difference that relates to right to mine assets is being amortized into income using the units of production method. Our equity in the earnings of OCI Wyoming is summarized as follows (in thousands): Three Months Ended Six Months Ended 2015 2014 2015 2014 (Unaudited) (Unaudited) Income allocation to NRP’s equity interests $ 12,786 $ 10,851 $ 26,513 $ 22,127 Amortization of basis difference (1,187 ) (1,450 ) (2,391 ) (2,947 ) Equity in earnings of unconsolidated investment $ 11,599 $ 9,401 $ 24,122 $ 19,180 The results of OCI Wyoming’s operations for the three and six months ended June 30, 2015 and 2014 are summarized as follows (in thousands): Three Months Ended Six Months Ended 2015 2014 2015 2014 (Unaudited) (Unaudited) Sales $ 122,200 $ 112,970 $ 242,630 $ 229,211 Gross profit 31,091 27,604 63,815 54,723 Net income 26,094 22,145 54,108 45,157 The financial position of OCI Wyoming at June 30, 2015 and December 31, 2014 are summarized as follows (in thousands): June 30, December 31, 2014 (Unaudited) Current assets $ 166,900 $ 200,622 Noncurrent assets 228,691 202,282 Current liabilities 46,367 47,704 Noncurrent liabilities 135,190 149,192

Plant and Equipment

Plant and Equipment	6 Months Ended
	Jun. 30, 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): June 30, December 31, (Unaudited) Plant and equipment at cost $ 108,234 $ 89,759 Construction in process 634 457 Less accumulated depreciation (31,581 ) (30,123 ) Total plant and equipment, net $ 77,287 $ 60,093 Depreciation expense related to the Partnership’s plant and equipment totaled $4.5 million and $1.2 million for the three months ended June 30, 2015 and 2014, respectively. Depreciation expense related to the Partnership’s plant and equipment totaled $9.0 million and $2.5 million for the six months ended June 30, 2015 and 2014, respectively. During the second quarter of 2015, the Partnership recorded $2.3 million of asset impairment expense related to a coal preparation plant.

Mineral Rights

Mineral Rights	6 Months Ended
	Jun. 30, 2015
Extractive Industries [Abstract]
Mineral Rights	5. Mineral Rights The Partnership’s mineral rights consist of the following (in thousands): June 30, December 31, (Unaudited) Coal $ 1,548,680 $ 1,541,572 Oil and Gas 578,791 560,395 Aggregates 236,283 211,490 Other 14,950 15,014 Less accumulated depletion and amortization (590,250 ) (546,619 ) Total mineral rights, net $ 1,788,454 $ 1,781,852 Depletion expense related to the Partnership’s mineral rights totaled $23.4 million and $14.2 million for the three months ended June 30, 2015 and 2014, respectively. Depletion expense related to the Partnership’s mineral rights totaled $43.3 million and $26.7 million for the six months ended June 30, 2015 and 2014, respectively. During the second quarter of 2015, the Partnership recorded $1.5 million of asset impairment expense related to its coal mineral rights.

Intangible Assets

Intangible Assets	6 Months Ended
	Jun. 30, 2015
Goodwill and Intangible Assets Disclosure [Abstract]
Intangible Assets	6. Intangible Assets The Partnership’s intangible assets consist of the following (in thousands): June 30, December 31, (Unaudited) Contract intangibles $ 81,109 $ 82,972 Other intangibles 4,998 3,004 Less accumulated amortization (26,925 ) (25,243 ) Total intangible assets, net $ 59,182 $ 60,733 Amortization expense related to the Partnership’s intangible assets totaled $1.2 million and $0.9 million for the three months ended June 30, 2015 and 2014, respectively. Amortization expense related to the Partnership’s intangible assets totaled $2.3 million and $1.8 million for the six months ended June 30, 2015 and 2014, respectively.

Debt and Debt-Affiliate

Debt and Debt-Affiliate	6 Months Ended
	Jun. 30, 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 June 30, 2015 and December 31, 2014, Debt and debt—affiliate consisted of the following (in thousands): June 30, December 31, (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% $ 422,545 $ 422,167 Opco Debt: $300 million floating rate revolving credit facility, due October 2017 215,000 — $300 million floating rate revolving credit facility, due August 2016 — 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 13,850 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 21,600 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 100,000 110,000 Total debt and debt—affiliate 1,432,118 1,475,223 Less: current portion of long-term debt, net (155,983 ) (80,983 ) Total long-term debt and debt—affiliate $ 1,276,135 $ 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. NRP and NRP Finance have the option to redeem the NRP Senior Notes, in whole or in part, at any time on or after April 1, 2016, at fixed redemption prices specified in the indenture governing the NRP Senior Notes (the “NRP Senior Notes Indenture”). Before April 1, 2016, NRP and NRP Finance may redeem all or part of the NRP Senior Notes at a redemption price equal to the sum of the principal plus a make whole premium at the redemption date, plus accrued and unpaid interest, if any, to the redemption date. Furthermore, before April 1, 2016, NRP and NRP Finance may on any one or more occasions redeem up to 35% of the aggregate principal amount of the notes with the net proceeds of certain public or private equity offerings at a redemption price of 109.125% of the principal amount of notes, plus any accrued and unpaid interest, if any, to the date of redemption, if at least 65% of the aggregate principal amount of the notes issued under the indenture remains outstanding immediately after such redemption and the redemption occurs within 180 days of the closing date of such equity offering. In the event of a change of control, as defined in the indenture, the holders of the notes may require NRP and NRP Finance to purchase their notes at a purchase price equal to 101% of the principal amount of the notes, plus accrued and unpaid interest, if any. The NRP Senior Notes Indenture contains additional covenants that, among other things, limit NRP’s ability and the ability of certain of its subsidiaries to declare or pay any dividend or distribution on, purchase or redeem units or purchase or redeem subordinated debt; make investments; create certain liens; enter into agreements that restrict distributions or other payments from NRP’s restricted subsidiaries as defined in the indenture to NRP; sell assets; consolidate, merge or transfer all or substantially all of the assets of NRP and its restricted subsidiaries; engage in transactions with affiliates; create unrestricted subsidiaries; and enter into certain sale and leaseback transactions. The NRP Senior Notes Indenture 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 NRP Senior Notes 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 threshholds. Opco Debt All of Opco’s debt is guaranteed by its wholly owned subsidiaries and is secured by certain of the assets of Opco and its wholly owned subsidiaries other than NRP Trona LLC, as further described below. As of June 30, 2015 and December 31, 2014, Opco was in compliance with the terms of the financial covenants contained in its debt agreements. Revolving Credit Facility In June 2015, Opco entered into a $300 million Third Amended and Restated Credit Agreement (the “A&R Revolving Credit Facility”), which amended and restated Opco’s $300 million Second Amended and Restated Credit Agreement due August 2016. The A&R Revolving Credit Facility matures on October 2, 2017, is guaranteed by all of Opco’s wholly owned subsidiaries, and is secured by liens on certain of the assets of Opco and its subsidiaries, as further described below. Initially, indebtedness under the A&R Revolving Credit Facility bears interest, at Opco’s option, at a rate of 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 2.375%; or • a rate equal to LIBOR plus 3.375%. Borrowings under the A&R Revolving Credit Facility will bear interest at such rate until the time that Opco delivers quarterly financial statements for the quarter ending September 30, 2015 to the lenders thereunder. Following such delivery date, indebtedness under the A&R Revolving Credit Facility will bear interest, at Opco’s option, at a rate of 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 1.50% to 2.50%; or • a rate equal to LIBOR plus an applicable margin ranging from 2.50% to 3.50%. The weighted average interest rates for the borrowings outstanding under the A&R Revolving Credit Facility for the six months ended June 30, 2015 and 2014 were 2.07% and 1.97%, respectively. The weighted average interest rates for the borrowings outstanding under the A&R Revolving Credit Facility for the three months ended June 30, 2015 and 2014 were 2.19% and 1.95%, respectively. Opco will incur a commitment fee on the unused portion of the revolving credit facility at a rate of 0.50% per annum. Opco may prepay all amounts outstanding under the A&R Revolving Credit Facility at any time without penalty. The A&R Revolving Credit Facility contains financial covenants requiring Opco to maintain: • a ratio of consolidated indebtedness to consolidated EBITDDA (as defined in the A&R Revolving Credit Facility) not to exceed: • 4.0 to 1.0 for each fiscal quarter ending on or before March 31, 2016; • 3.75 to 1.0 for each subsequent fiscal quarter ending on or before March 31, 2017; and • 3.5 to 1.0 for each fiscal quarter ending on or after June 30, 2017; and • a ratio of consolidated EBITDDA to consolidated fixed charges (consisting of consolidated interest expense and consolidated lease expense) of not less than 3.5 to 1.0. The A&R Revolving Credit Facility contains certain additional customary negative covenants that, among other items, restrict Opco’s ability to incur additional debt, grant liens on its assets, make investments, sell assets and engage in business combinations. Included in the investment covenant are restrictions upon Opco’s ability to acquire assets where Opco does not maintain certain levels of liquidity. The A&R Revolving Credit Facility also contains customary events of default, including cross-defaults under Opco’s senior notes and Term Loan (as described below). The A&R Revolving Credit Facility is collateralized and secured by liens on certain of Opco’s assets with a carrying value of $810.5 million classified as Mineral rights and Plant and equipment on the Partnership’s Consolidated Balance Sheet as of June 30, 2015. The collateral includes (1) the equity interests in all of Opco’s wholly owned subsidiaries, other than NRP Trona LLC (which owns a 49% non-controlling equity interest in OCI Wyoming), (2) the personal property and fixtures owned by Opco’s wholly owned subsidiaries, other than NRP Trona LLC, (3) Opco’s material coal royalty revenue producing properties, (4) real property associated with certain of VantaCore’s construction aggregates mining operations, and (5) certain of Opco’s coal-related infrastructure assets. In conjunction with the entry into the A&R Revolving Credit Facility, approximately $85 million of commitments under the previous revolving credit facility that matured in August 2016 were replaced by new lenders. Extinguishment accounting was applied for lenders participating in the previous revolving credit facility but not participating or participating to a lesser extent in the A&R Revolving Credit Facility. This accounting resulted in a write off of $0.2 million of debt issuance costs in June 2015. Term Loan During 2013, Opco entered into a $200 million Term Loan facility (the “Term Loan”). The weighted average interest rates for the debt outstanding under the Term Loan for the six months ended June 30, 2015 and 2014 were 2.19% and 2.25%, respectively. The weighted average interest rates for the debt outstanding under the Term Loan for the three months ended June 30, 2015 and 2014 were 2.19% and 2.24%, 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. In connection with the entry into the A&R Revolving Credit Facility in June 2015, Opco and its subsidiaries entered into the Second Amendment (the “Term Loan Amendment”) to the Term Loan. The Term Loan Amendment amends the Term Loan to provide for the security thereof by the same collateral package pledged by Opco and its subsidiaries to secure the A&R Revolving Credit Facility, as described above. Senior Notes Opco made principal payments of $48.3 million on its senior notes during the six months ended June 30, 2015. The Note Purchase Agreements relating to Opco’s senior notes contain 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. In connection with the entry into the A&R Revolving Credit Facility in June 2015, Opco entered into the Third Amendment to the Note Purchase Agreements (the “NPA Amendment”) that provides for the security of the senior notes by the same collateral package pledged by Opco and its subsidiaries to secure the A&R Revolving Credit Facility and the Term Loan, as described above. In addition, the NPA Amendment includes a covenant that provides that, in the event Opco or any of its subsidiaries is subject to any additional or more restrictive covenants under the agreements governing its material indebtedness (including the A&R Revolving Credit Facility, the Term Loan, and all renewals, amendments or restatements thereof), such covenants shall be deemed to be incorporated by reference in the senior notes and the holders of the senior notes shall receive the benefit of such additional or more restrictive covenants to the same extent as the lenders under such material indebtedness agreement. NRP Oil and Gas Debt Revolving Credit Facility In August 2013, NRP Oil and Gas entered into a 5-year, $100.0 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 $500.0 million with an initial borrowing base of $137.0 million, and the maturity date thereof was extended to November 2019. 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. In April 2015, the lenders completed their semi-annual redetermination of the borrowing base under the NRP Oil and Gas revolving credit facility and the $137.0 million borrowing base under that facility was redetermined at $105.0 million that also resulted in a write off of $0.6 million of debt issuance costs in April 2015. The Partnership repaid $10.0 million of outstanding borrowings under the NRP Oil and Gas revolving credit facility during the second quarter of 2015. At June 30, 2015 and December 31, 2014, there was $100.0 million and $110.0 million, respectively, outstanding under the NRP Oil and Gas revolving credit facility. 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. The weighted average interest rates for the debt outstanding under the credit facility for each of the six month periods ended June 30, 2015 and 2014 was 2.52% and 1.90%, respectively. The weighted average interest rates for the debt outstanding under the credit facility for each of the three month periods ended June 30, 2015 and 2014 were 2.63% and 1.90%, 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 June 30, 2015 and December 31, 2014, NRP Oil and Gas was in compliance with the terms of the financial covenants contained in its credit facility.

Fair Value Measurements

Fair Value Measurements	6 Months Ended
	Jun. 30, 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: June 30, 2015 December 31, 2014 Carrying Estimated Carrying Estimated (Unaudited) Assets Contracts receivable—affiliate, current and long-term (1) $ 4,833 $ 5,174 $ 4,870 $ 5,162 Debt and debt—affiliate NRP LP senior notes (2) $ 422,545 $ 372,406 $ 422,167 $ 423,780 Opco revolving credit facility and term loan facility (3) $ 290,000 $ 290,000 $ 275,000 $ 275,000 Opco senior notes and utility local improvement obligation (1) $ 619,573 $ 542,901 $ 668,056 $ 672,740 NRP Oil and Gas revolving credit facility (3) $ 100,000 $ 100,000 $ 110,000 $ 110,000 (1) The Level 3 estimated fair value was based on inputs that are observable in the market or that could be derived from, or collaborated with, observable market data, including quotations obtained for similar instruments on the closing trading prices near quarter end. (2) The Level 2 estimated fair value was based upon quotations obtained for similar instruments on the closing trading prices near quarter end. (3) 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. The March 31, 2015 estimated fair value of the NRP LP senior notes and Opco senior notes and local utility improvement obligation were presented incorrectly as $417.0 million and $629.5 million, respectively, and should have been presented as $378.3 million and $557.9 million, respectively. The estimated fair value disclosure had no impact on the Partnership’s overall financial position, income or cash flows.

Related Party Transactions

Related Party Transactions	6 Months Ended
	Jun. 30, 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 (“WPPLP”). The Partnership had Accounts payable—affiliates to Quintana Minerals Corporation of $0.6 million at both June 30, 2015 and December 31, 2014, for services provided by Quintana Minerals Corporation to the Partnership. The Partnership had Accounts payable—affiliates to WPPLP of $0.3 million and $0.4 million at June 30, 2015 and December 31, 2014, respectively. The reimbursements to affiliates of the Partnership’s general partner for services performed by WPPLP and Quintana Minerals Corporation are as follows (in thousands): Three Months Ended June 30, Six Months Ended June 30, 2015 2014 2015 2014 (Unaudited) (Unaudited) General and administrative—affiliate $ 3,535 $ 3,000 $ 7,321 $ 6,094 The Partnership also leases an office building in Huntington, West Virginia from WPPLP and recorded $0.2 million and $0.3 million in General and administrative—affiliates in each of the three and six months ended June 30, 2015 and 2014, respectively. 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 Foresight Energy LP (“Foresight Energy”) totaled $31.6 million and $20.4 million for the three months ended June 30, 2015 and 2014, respectively. Coal related revenues from Foresight Energy totaled $49.9 million and $38.3 million for the six months ended June 30, 2015 and 2014, respectively. As of June 30, 2015 and December 31, 2014 the Partnership had Accounts receivable-affiliate from Foresight Energy of $8.2 million and $9.2 million, respectively. As of June 30, 2015, the Partnership had received $86.8 million in minimum royalty payments to date that have not been recorded as revenue since they have not been recouped by Foresight Energy. The Partnership owns and leases rail load out and associated facilities to Foresight Energy at Foresight Energy’s Sugar Camp mine. The lease agreement is accounted for as a direct financing lease. Total projected remaining payments under the lease at June 30, 2015 were $83.8 million with unearned income of $37.1 million, and the net amount receivable was $46.7 million, of which $1.9 million is included in Accounts receivable—affiliate 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—affiliate while the remaining is included in Long-term contracts receivable—affiliate on the accompanying Consolidated Balance Sheets. The Partnership holds a contractual overriding royalty interest from a subsidiary of Foresight Energy that provides for payments based upon production from specific tons at Foresight Energy’s 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 June 30, 2015 was $4.8 million, of which $0.4 million is included in Accounts receivable — — In April 2015, the Partnership recognized a gain of $9.3 million on a reserve swap at Foresight Energy’s Williamson mine. The gain is included in Coal related revenues—affiliates on our Consolidated Statements of Comprehensive Income. The Level 3 fair value of the reserves was estimated using a cash flow model. The expected cash flows were developed using estimated annual sales tons, forecasted sales prices and anticipated market royalty rates. 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 June 30, 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. (“Quintana Capital”), 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 June 30, 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 $0.7 million and $1.5 million and $1.6 million for the three and six months ended June 30, 2015 and 2014, respectively. As of June 30, 2015, the Partnership had recorded $0.3 million in minimum royalty payments to date that have not been recognized as revenue since they have not been recouped by Corsa. The Partnership also had Accounts receivable—affiliate totaling $0.2 million and $0.3 million from Corsa at June 30, 2015 and December 31, 2014, respectively. WPPLP Production Royalty For the three and six months ended June 30, 2015, we recorded $0.1 million in Coal related expenses—affiliates related to a non-participating production royalty payable to WPPLP pursuant to a conveyance agreement entered into in 2007.

Major Lessees

Major Lessees	6 Months Ended
	Jun. 30, 2015
Risks and Uncertainties [Abstract]
Major Lessees	10. Major Lessees Revenues from lessees that exceeded ten percent of total revenues and other income for periods presented below are as follows (in thousands except for percentages): Three Months Ended June 30, Six Months Ended June 30, 2015 2014 2015 2014 (Unaudited) (Unaudited) Revenues Percent Revenues Percent Revenues Percent Revenues Percent Foresight Energy and affiliates $ 31,581 23 % $ 20,432 23 % $ 49,879 20 % $ 38,254 22 % Alpha Natural Resources 8,943 6 % 12,810 14 % 17,772 7 % 24,451 14 % The Partnership has a significant concentration of revenues with Foresight Energy and Alpha Natural Resources, 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 12% and 9% of the Partnership’s total revenues and other income for the three and six months ended June 30, 2015, respectively. For the three and six months ended June 30, 2014, the Williamson mine was responsible for approximately 10% and 11% of the Partnership’s total revenues and other income, respectively.

Long-Term Incentive Plans

Long-Term Incentive Plans	6 Months Ended
	Jun. 30, 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 498,486 Grants vested and paid during the year (290,430 ) Forfeitures during the year (23,875 ) Outstanding grants at June 30, 2015 1,337,574 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 0.31% to 1.35% and 39.41% to 53.35%, respectively, at June 30, 2015. The Partnership’s average distribution rate of 7.60% and historical forfeiture rate of 4.97% were used in the calculation at June 30, 2015. The Partnership recorded a credit to general and administrative expenses (“G&A expenses”) related to its plan to be reimbursed to its general partner of $1.4 million and $1.5 million for the three and six months ended June 30, 2015, respectively, due to the decline in the market price of the Partnership’s units during 2015. For the three and six months ended June 30 2014, the Partnership recorded G&A expenses of $1.5 million and $0.4 million, respectively. 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 six month periods ended June 30, 2015 and 2014, respectively. In connection with the phantom unit awards, the Compensation, Nominating and Governance 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 between the date the units are granted and the vesting date. 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 June 30, 2015 and June 30, 2014 was $3.2 million and $9.4 million, respectively.

Distributions Paid

Distributions Paid	6 Months Ended
	Jun. 30, 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. On May 14, 2015, the Partnership paid a quarterly distribution of $0.09 per unit to all holders of common units on May 5, 2015. On January 31, 2014, the Partnership paid a quarterly distribution of $0.35 per unit to all holders of common units on January 21, 2014. On May 14, 2014, the Partnership paid a quarterly distribution of $0.35 per unit to all holders of common units on May 5, 2014.

Commitments and Contingencies

Commitments and Contingencies	6 Months Ended
	Jun. 30, 2015
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	13. Commitments and Contingencies The purchase agreement for the acquisition of the Partnership’s interest in OCI Wyoming requires it 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 quarters of 2014 and 2015, the Partnership paid $3.8 million and $0.5 million, respectively, in contingent consideration to Anadarko. As of June 30, 2015, the Partnership has estimated and recorded $8.8 million as an accrued liability on its consolidated Balance Sheet, 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. 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 were still considering this claim against the Partnership. The Partnership responded in writing in May 2015 and does not believe the reorganization transactions triggered an obligation to pay the additional contingent consideration. The Partnership will continue to engage in discussions with Anadarko to resolve the issue to the extent necessary. 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. Since 2013, several citizen group lawsuits have been filed against landowners alleging ongoing discharges of pollutants, including selenium and conductivity, from valley fills located at reclaimed mountaintop removal mining sites in West Virginia. In each case, the mine on the subject property had been closed, the property had been reclaimed, and the state reclamation bond had been released. Any determination that a landowner or lessee has liability for discharges from a previously reclaimed mine site could result in substantial compliance costs or fines and would result in uncertainty as to continuing liability for completed and reclaimed coal mine operations. A subsidiary of the Partnership has been named as a defendant in one of these lawsuits. Given the stage of this ongoing litigation, the Partnership currently cannot reasonably estimate a range of potential loss, if any, related to this matter.

Subsequent Events

Subsequent Events	6 Months Ended
	Jun. 30, 2015
Subsequent Events [Abstract]
Subsequent Events	14. Subsequent Events The following represents material events that have occurred subsequent to June 30, 2015 through the time of the Partnership’s filing of this Quarterly Report on Form 10-Q with the Securities and Exchange Commission: Alpha Natural Resources Bankruptcy On August 3, 2015, Alpha Natural Resources, the Partnership’s second largest coal lessee, filed a petition for reorganization under Chapter 11 of the U.S. Bankruptcy Code. During the course of the bankruptcy, Alpha is expected to continue operations and pay royalties to the Partnership. In the second quarter of 2015, the Partnership recognized $8.9 million in revenues from Alpha, equivalent to 6.5% of the Partnership’s total revenues. Ultimately, Alpha will determine whether to assume or reject the coal leases that it has with the Partnership in the bankruptcy process. The Partnership currently anticipates that the majority of its active leases with Alpha will be assumed. At the time of the bankruptcy filing, Alpha estimated that it owed the Partnership approximately $2.5 million in pre-petition amounts for royalties on July 2015 production, which would have become due and payable in late August. The Partnership will receive all pre-petition amounts due to it with respect to any leases that are assumed in the bankruptcy. Hillsboro Mine Force Majeure Notice In July 2015, we received a notice from Foresight Energy declaring a force majeure event at the Hillsboro mine due to elevated carbon monoxide levels at the mine. While we are disputing Foresight Energy’s claim, the effect of a valid force majeure declaration would relieve Foresight Energy of its obligation to pay us the quarterly minimum deficiency payment with respect to the Hillsboro mine in the second quarter. Foresight Energy’s failure to make the deficiency payment with respect to the second quarter resulted in a $3.1 million cash impact to the Partnership. On July 28, 2015, Foresight Energy announced that mining at the Hillsboro mine had re-commenced. We received $4.4 million in royalty payments on tonnage sold from coal stockpiles at the Hillsboro mine during the second quarter of 2015. Distributions Declared On July 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 August 14, 2015 to unitholders of record on August 5, 2015.

Basis of Presentation (Policies

Basis of Presentation (Policies)	6 Months Ended
	Jun. 30, 2015
Organization, Consolidation and Presentation of Financial Statements [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 six months ended June 30, 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, 2017, 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)	6 Months Ended
	Jun. 30, 2015
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 and six months ended June 30, 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 June 30, 2014 Six Months Ended June 30, 2014 (Unaudited) (In thousands) Revenues and other income except aggregates related and oil and gas related revenues $ 69,213 $ 136,088 Aggregates related revenues 49,094 82,261 Oil and gas related revenues 34,636 62,528 Total revenues and other income $ 152,943 $ 280,877 Net income $ 36,752 $ 69,524 Basic and diluted net income per common unit $ 0.33 $ 0.62
VantaCore Partners LLC [Member]
Schedule of Accounting for Acquisition	The accounting for the VantaCore acquisition was completed in the second quarter of 2015 and is summarized as follows: VantaCore Purchase Price Allocation October 1, 2014 (In thousands) Consideration Cash $ 168,978 NRP common units 31,604 Total consideration given $ 200,582 Allocation of Purchase Price Current assets $ 37,222 Land, property and equipment 62,911 Mineral rights 111,500 Other assets 4,347 Current liabilities (16,953 ) Asset retirement obligation (3,285 ) Goodwill 4,840 Fair value of net assets acquired $ 200,582
Sanish Field [Member]
Schedule of Accounting for Acquisition	The results of operations of the acquisition have been included in our consolidated financial statements since the acquisition date. The accounting for the Sanish Field acquisition was completed in the second quarter of 2015 without significant changes during the measurement period and is summarized as follows: Sanish Field Purchase Price Allocation November 12, 2014 (In thousands) Consideration Cash $ 339,093 Allocation of Purchase Price Mineral rights - proven oil and gas properties 298,293 Mineral rights - probable and possible oil and gas resources 40,800 Fair value of net assets acquired $ 339,093

Equity Investment (Tables)

Equity Investment (Tables)	6 Months Ended
	Jun. 30, 2015
Equity Method Investments and Joint Ventures [Abstract]
Summary of Equity in Earnings of OCI Wyoming	Our equity in the earnings of OCI Wyoming is summarized as follows (in thousands): Three Months Ended Six Months Ended 2015 2014 2015 2014 (Unaudited) (Unaudited) Income allocation to NRP’s equity interests $ 12,786 $ 10,851 $ 26,513 $ 22,127 Amortization of basis difference (1,187 ) (1,450 ) (2,391 ) (2,947 ) Equity in earnings of unconsolidated investment $ 11,599 $ 9,401 $ 24,122 $ 19,180
Schedule of Summarized Financial Information	The results of OCI Wyoming’s operations for the three and six months ended June 30, 2015 and 2014 are summarized as follows (in thousands): Three Months Ended Six Months Ended 2015 2014 2015 2014 (Unaudited) (Unaudited) Sales $ 122,200 $ 112,970 $ 242,630 $ 229,211 Gross profit 31,091 27,604 63,815 54,723 Net income 26,094 22,145 54,108 45,157 The financial position of OCI Wyoming at June 30, 2015 and December 31, 2014 are summarized as follows (in thousands): June 30, December 31, 2014 (Unaudited) Current assets $ 166,900 $ 200,622 Noncurrent assets 228,691 202,282 Current liabilities 46,367 47,704 Noncurrent liabilities 135,190 149,192

Plant and Equipment (Tables)

Plant and Equipment (Tables)	6 Months Ended
	Jun. 30, 2015
Property, Plant and Equipment [Abstract]
Plant and Equipment	The Partnership’s plant and equipment consist of the following (in thousands): June 30, December 31, (Unaudited) Plant and equipment at cost $ 108,234 $ 89,759 Construction in process 634 457 Less accumulated depreciation (31,581 ) (30,123 ) Total plant and equipment, net $ 77,287 $ 60,093

Mineral Rights (Tables)

Mineral Rights (Tables)	6 Months Ended
	Jun. 30, 2015
Extractive Industries [Abstract]
Mineral Rights	The Partnership’s mineral rights consist of the following (in thousands): June 30, December 31, (Unaudited) Coal $ 1,548,680 $ 1,541,572 Oil and Gas 578,791 560,395 Aggregates 236,283 211,490 Other 14,950 15,014 Less accumulated depletion and amortization (590,250 ) (546,619 ) Total mineral rights, net $ 1,788,454 $ 1,781,852

Intangible Assets (Tables)

Intangible Assets (Tables)	6 Months Ended
	Jun. 30, 2015
Goodwill and Intangible Assets Disclosure [Abstract]
Intangible Assets	The Partnership’s intangible assets consist of the following (in thousands): June 30, December 31, (Unaudited) Contract intangibles $ 81,109 $ 82,972 Other intangibles 4,998 3,004 Less accumulated amortization (26,925 ) (25,243 ) Total intangible assets, net $ 59,182 $ 60,733

Debt and Debt-Affiliate (Tables

Debt and Debt-Affiliate (Tables)	6 Months Ended
	Jun. 30, 2015
Debt Disclosure [Abstract]
Debt	As of June 30, 2015 and December 31, 2014, Debt and debt—affiliate consisted of the following (in thousands): June 30, December 31, (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% $ 422,545 $ 422,167 Opco Debt: $300 million floating rate revolving credit facility, due October 2017 215,000 — $300 million floating rate revolving credit facility, due August 2016 — 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 13,850 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 21,600 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 100,000 110,000 Total debt and debt—affiliate 1,432,118 1,475,223 Less: current portion of long-term debt, net (155,983 ) (80,983 ) Total long-term debt and debt—affiliate $ 1,276,135 $ 1,394,240

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	6 Months Ended
	Jun. 30, 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: June 30, 2015 December 31, 2014 Carrying Estimated Carrying Estimated (Unaudited) Assets Contracts receivable—affiliate, current and long-term (1) $ 4,833 $ 5,174 $ 4,870 $ 5,162 Debt and debt—affiliate NRP LP senior notes (2) $ 422,545 $ 372,406 $ 422,167 $ 423,780 Opco revolving credit facility and term loan facility (3) $ 290,000 $ 290,000 $ 275,000 $ 275,000 Opco senior notes and utility local improvement obligation (1) $ 619,573 $ 542,901 $ 668,056 $ 672,740 NRP Oil and Gas revolving credit facility (3) $ 100,000 $ 100,000 $ 110,000 $ 110,000 (1) The Level 3 estimated fair value was based on inputs that are observable in the market or that could be derived from, or collaborated with, observable market data, including quotations obtained for similar instruments on the closing trading prices near quarter end. (2) The Level 2 estimated fair value was based upon quotations obtained for similar instruments on the closing trading prices near quarter end. (3) 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.

Related Party Transactions (Tab

Related Party Transactions (Tables)	6 Months Ended
	Jun. 30, 2015
Related Party Transactions [Abstract]
Summary of Reimbursements	The reimbursements to affiliates of the Partnership’s general partner for services performed by WPPLP and Quintana Minerals Corporation are as follows (in thousands): Three Months Ended June 30, Six Months Ended June 30, 2015 2014 2015 2014 (Unaudited) (Unaudited) General and administrative—affiliate $ 3,535 $ 3,000 $ 7,321 $ 6,094

Major Lessees (Tables)

Major Lessees (Tables)	6 Months Ended
	Jun. 30, 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 periods presented below are as follows (in thousands except for percentages): Three Months Ended June 30, Six Months Ended June 30, 2015 2014 2015 2014 (Unaudited) (Unaudited) Revenues Percent Revenues Percent Revenues Percent Revenues Percent Foresight Energy and affiliates $ 31,581 23 % $ 20,432 23 % $ 49,879 20 % $ 38,254 22 % Alpha Natural Resources 8,943 6 % 12,810 14 % 17,772 7 % 24,451 14 %

Long-Term Incentive Plans (Tabl

Long-Term Incentive Plans (Tables)	6 Months Ended
	Jun. 30, 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 498,486 Grants vested and paid during the year (290,430 ) Forfeitures during the year (23,875 ) Outstanding grants at June 30, 2015 1,337,574

Basis of Presentation - Additio

Basis of Presentation - Additional Information (Detail) - 6 months ended Jun. 30, 2015 - USD ($) $ in Millions	Total
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 Infor

Acquisitions - Additional Information (Detail) $ in Thousands	Nov. 12, 2014USD ($)	Oct. 01, 2014USD ($)PlantQuarry	Jun. 30, 2015USD ($)	Mar. 31, 2015USD ($)
Business Acquisition [Line Items]
Increase in plant and equipment acquired				$ 22,500
Increase in mineral rights, net and intangible assets, net			$ 24,700
VantaCore Partners LLC [Member]
Business Acquisition [Line Items]
Aggregate acquisition cost		$ 200,582
Number of hard rock quarries | Quarry		4
Number of sand and gravel plants | Plant		5
Number of asphalt plants | Plant		2
Sanish Field [Member]
Business Acquisition [Line Items]
Aggregate acquisition cost	$ 339,093

Acquisitions - Schedule of Acco

Acquisitions - Schedule of Accounting for Acquisition (Detail) - USD ($) $ in Thousands	Nov. 12, 2014	Oct. 01, 2014	Jun. 30, 2015	Dec. 31, 2014
Allocation of Purchase Price
Goodwill			$ 4,840	$ 52,012
VantaCore Partners LLC [Member]
Consideration
Cash		$ (168,978)
NRP common units		31,604
Total consideration given		200,582
Allocation of Purchase Price
Current assets		37,222
Land, property and equipment		62,911
Mineral rights		111,500
Other assets		4,347
Current liabilities		(16,953)
Asset retirement obligation		(3,285)
Goodwill		4,840
Fair value of net assets acquired		$ 200,582
Sanish Field [Member]
Consideration
Cash	$ 339,093
Total consideration given	339,093
Allocation of Purchase Price
Mineral rights - proven oil and gas properties	298,293
Mineral rights - probable and possible oil and gas resources	40,800
Fair value of net assets acquired	$ 339,093

Acquisitions - Business Acquisi

Acquisitions - Business Acquisition Pro Forma Financial Information (Unaudited) (Detail) - Jun. 30, 2014 - USD ($) $ / shares in Units, $ in Thousands	Total	Total
Business Combinations [Abstract]
Revenues and other income except aggregates related and oil and gas related revenues	$ 69,213	$ 136,088
Aggregates related revenues	49,094	82,261
Oil and gas related revenues	34,636	62,528
Total revenues and other income	152,943	280,877
Net income	$ 36,752	$ 69,524
Basic and diluted net income per common unit	$ 0.33	$ 0.62

Equity Investment - Additional

Equity Investment - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Schedule of Equity Method Investments [Line Items]
Distributions from Equity Method Investment			$ 21,805	$ 21,935
OCI Wyoming [Member]
Schedule of Equity Method Investments [Line Items]
Distributions from Equity Method Investment	$ 10,900	$ 13,900	$ 21,800	$ 25,600
Percentage of partnership interest owned	49.00%		49.00%
Difference between carried amount of investment and underlying equity	$ 157,600		$ 157,600		$ 162,700

Equity Investment - Summary of

Equity Investment - Summary of Equity in Earnings of OCI Wyoming (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Schedule of Equity Method Investments [Line Items]
Equity in earnings of unconsolidated investment	$ 11,599	$ 9,401	$ 24,122	$ 19,180
OCI Wyoming [Member]
Schedule of Equity Method Investments [Line Items]
Income allocation to NRP's equity interests	12,786	10,851	26,513	22,127
Amortization of basis difference	(1,187)	(1,450)	(2,391)	(2,947)
Equity in earnings of unconsolidated investment	$ 11,599	$ 9,401	$ 24,122	$ 19,180

Equity Investment - Schedule of

Equity Investment - Schedule of Summarized Financial Information (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Schedule of Equity Method Investments [Line Items]
Net income	$ 31,334	$ 31,407	$ 48,823	$ 64,012
Current assets	99,927		99,927		$ 136,118
Current liabilities	219,538		219,538		147,931
OCI Wyoming [Member]
Schedule of Equity Method Investments [Line Items]
Sales	122,200	112,970	242,630	229,211
Gross profit	31,091	27,604	63,815	54,723
Net income	26,094	$ 22,145	54,108	$ 45,157
Current assets	166,900		166,900		200,622
Noncurrent assets	228,691		228,691		202,282
Current liabilities	46,367		46,367		47,704
Noncurrent liabilities	$ 135,190		$ 135,190		$ 149,192

Plant and Equipment - Plant and

Plant and Equipment - Plant and Equipment (Detail) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Property, Plant and Equipment [Abstract]
Plant and equipment at cost	$ 108,234	$ 89,759
Construction in process	634	457
Less accumulated depreciation	(31,581)	(30,123)
Total plant and equipment, net	$ 77,287	$ 60,093

Plant and Equipment - Additiona

Plant and Equipment - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Property, Plant and Equipment [Line Items]
Total depreciation and amortization expense on plant and equipment	$ 4,500	$ 1,200	$ 9,000	$ 2,500
Asset impairment charges	3,803	$ 5,624	$ 3,803	$ 5,624
Coal Preparation Plant [Member]
Property, Plant and Equipment [Line Items]
Asset impairment charges	$ 2,300

Mineral Rights - Mineral Rights

Mineral Rights - Mineral Rights (Detail) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Costs Incurred, Oil and Gas Property Acquisition, Exploration, and Development Activities [Line Items]
Less accumulated depletion and amortization	$ (590,250)	$ (546,619)
Total mineral rights, net	1,788,454	1,781,852
Coal [Member]
Costs Incurred, Oil and Gas Property Acquisition, Exploration, and Development Activities [Line Items]
Partnership's mineral rights	1,548,680	1,541,572
Oil And Gas [Member]
Costs Incurred, Oil and Gas Property Acquisition, Exploration, and Development Activities [Line Items]
Partnership's mineral rights	578,791	560,395
Aggregate [Member]
Costs Incurred, Oil and Gas Property Acquisition, Exploration, and Development Activities [Line Items]
Partnership's mineral rights	236,283	211,490
Other [Member]
Costs Incurred, Oil and Gas Property Acquisition, Exploration, and Development Activities [Line Items]
Partnership's mineral rights	$ 14,950	$ 15,014

Mineral Rights - Additional Inf

Mineral Rights - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Costs Incurred, Oil and Gas Property Acquisition, Exploration, and Development Activities [Line Items]
Total depletion and amortization expense on mineral rights	$ 23,400	$ 14,200	$ 43,300	$ 26,700
Asset impairment charges	3,803	$ 5,624	$ 3,803	$ 5,624
Coal and Mineral Rights [Member]
Costs Incurred, Oil and Gas Property Acquisition, Exploration, and Development Activities [Line Items]
Asset impairment charges	$ 1,500

Intangible Assets - Intangible

Intangible Assets - Intangible Assets (Detail) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Goodwill and Intangible Assets Disclosure [Abstract]
Contract intangibles	$ 81,109	$ 82,972
Other intangibles	4,998	3,004
Less accumulated amortization	(26,925)	(25,243)
Total intangible assets, net	$ 59,182	$ 60,733

Intangible Assets - Additional

Intangible Assets - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Goodwill and Intangible Assets Disclosure [Abstract]
Total amortization expense on intangible assets	$ 1.2	$ 0.9	$ 2.3	$ 1.8

Debt and Debt-Affiliate - Addit

Debt and Debt-Affiliate - Additional Information (Detail) - USD ($)	1 Months Ended				3 Months Ended					6 Months Ended		9 Months Ended	12 Months Ended
	Jun. 30, 2015	Apr. 30, 2015	Sep. 30, 2013	Aug. 31, 2013	Sep. 30, 2015	Jun. 30, 2015	Dec. 31, 2014	Jun. 30, 2014	Sep. 30, 2013	Jun. 30, 2015	Jun. 30, 2014	Mar. 31, 2016	Dec. 31, 2013	Oct. 31, 2014
Debt Instrument [Line Items]
Floating rate revolving credit facility	$ 1,432,118,000					$ 1,432,118,000	$ 1,475,223,000			$ 1,432,118,000
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Weighted average interest rate						2.19%		1.95%		2.07%	1.97%
OCI Wyoming [Member]
Debt Instrument [Line Items]
Percentage of partnership interest owned	49.00%					49.00%				49.00%
OCI Wyoming [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Percentage of partnership interest owned	49.00%					49.00%				49.00%
NRP LP Senior Notes [Member] | Scenario Forecast [Member]
Debt Instrument [Line Items]
Debt instrument, Redemption price, Percentage												109.125%
Redemption price at Change Of Control event, as a percentage of principal												101.00%
Term Loan [Member]
Debt Instrument [Line Items]
Repayment of principal amount							24,000,000		$ 101,000,000
Weighted average interest rate						2.19%		2.24%		2.19%	2.25%
Amount received from debt issuance													$ 200,000,000
Borrowings outstanding	$ 75,000,000					$ 75,000,000				$ 75,000,000
Maximum [Member] | NRP LP Senior Notes [Member] | Scenario Forecast [Member]
Debt Instrument [Line Items]
Debt instrument, Redemption price, Percentage of principal amount may redeemed												35.00%
Redemption Period From Equity Offering Closing Period												180 days
Minimum [Member] | NRP LP Senior Notes [Member] | Scenario Forecast [Member]
Debt Instrument [Line Items]
Debt instrument, Redemption price, percentage of principal remaining after redemption												65.00%
NRP LP [Member]
Debt Instrument [Line Items]
Floating rate revolving credit facility			$ 300,000,000						$ 300,000,000					$ 125,000,000
Repayment of principal amount			289,000,000
Proceeds from issuance of cost			$ 122,600,000
NRP LP [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Rate of senior notes	9.125%		9.125%			9.125%			9.125%	9.125%				9.125%
Senior Note issue percentage			99.007%						99.007%					99.50%
NRP LP [Member] | Maximum [Member]
Debt Instrument [Line Items]
Fixed charge coverage ratio	2					2				2
NRP LP [Member] | Minimum [Member]
Debt Instrument [Line Items]
Fixed charge coverage ratio	1					1				1
Opco [Member]
Debt Instrument [Line Items]
Ratio of consolidated indebtedness to consolidated EBITDDA										4
Ratio of consolidated EBITDDA to consolidated fixed charges										3.5
Principal payments on its senior notes										$ 48,300,000
Percentage of consolidated net tangible assets debt of subsidiaries not permitted to exceed										10.00%
Opco [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Commitment fee on the undrawn portion of the revolving credit facility rates										0.50
Ratio of consolidated EBITDDA to consolidated fixed charges										3.5
Carrying value of secured revolving credit facility	$ 810,500,000					$ 810,500,000				$ 810,500,000
Commitments under revolving credit facility										$ 85,000,000
Write off of debt issuance costs	$ 200,000
Opco [Member] | Revolving Credit Facility [Member] | Federal Funds Rate [Member]
Debt Instrument [Line Items]
Interest rate spread for base rate										0.50%
Opco [Member] | Revolving Credit Facility [Member] | LIBOR [Member]
Debt Instrument [Line Items]
Interest rate spread for base rate										1.00%
Opco [Member] | Revolving Credit Facility [Member] | Scenario Forecast [Member] | Federal Funds Rate [Member]
Debt Instrument [Line Items]
Interest rate spread for base rate					0.50%
Opco [Member] | Revolving Credit Facility [Member] | Scenario Forecast [Member] | LIBOR [Member]
Debt Instrument [Line Items]
Interest rate spread for base rate					1.00%
Opco [Member] | Revolving Credit Facility Basis Spread Condition One [Member] | Revolving Credit Facility [Member] | LIBOR [Member]
Debt Instrument [Line Items]
Applicable margin interest rate										2.375%
Opco [Member] | Revolving Credit Facility Basis Spread Condition Two [Member] | Revolving Credit Facility [Member] | LIBOR [Member]
Debt Instrument [Line Items]
Applicable margin interest rate										3.375%
Opco [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Additional interest accrue	2.00%					2.00%				2.00%
Partnership leverage ratio										3.75
Opco [Member] | Term Loan [Member]
Debt Instrument [Line Items]
Leverage ratio, maximum										4
Minimum interest coverage ratio										3.5
Opco [Member] | $300 Million Floating Rate Revolving Credit Facility, Due October 2017 [Member]
Debt Instrument [Line Items]
Floating rate revolving credit facility	$ 215,000,000					$ 215,000,000				$ 215,000,000
Revolving credit facility current borrowing base	$ 300,000,000					300,000,000				300,000,000
Opco [Member] | $300 Million Floating Rate Revolving Credit Facility, Due October 2017 [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Line of credit facility maturity date	Oct. 2, 2017
Opco [Member] | $300 Million Floating Rate Revolving Credit Facility, Due August 2016 [Member]
Debt Instrument [Line Items]
Floating rate revolving credit facility							200,000,000
Revolving credit facility current borrowing base	$ 300,000,000					300,000,000				$ 300,000,000
Opco [Member] | Maximum [Member] | Revolving Credit Facility Basis Spread Condition One [Member] | Revolving Credit Facility [Member] | Scenario Forecast [Member] | LIBOR [Member]
Debt Instrument [Line Items]
Applicable margin interest rate					2.50%
Opco [Member] | Maximum [Member] | Revolving Credit Facility Basis Spread Condition Two [Member] | Revolving Credit Facility [Member] | Scenario Forecast [Member] | LIBOR [Member]
Debt Instrument [Line Items]
Applicable margin interest rate					3.50%
Opco [Member] | Minimum [Member] | Revolving Credit Facility Basis Spread Condition One [Member] | Revolving Credit Facility [Member] | Scenario Forecast [Member] | LIBOR [Member]
Debt Instrument [Line Items]
Applicable margin interest rate					1.50%
Opco [Member] | Minimum [Member] | Revolving Credit Facility Basis Spread Condition Two [Member] | Revolving Credit Facility [Member] | Scenario Forecast [Member] | LIBOR [Member]
Debt Instrument [Line Items]
Applicable margin interest rate					2.50%
Opco [Member] | Fiscal Quarter Ending on or Before March 31, 2016 [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Ratio of consolidated indebtedness to consolidated EBITDDA										4
Opco [Member] | Fiscal Quarter Ending on or Before March 31, 2017 [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Ratio of consolidated indebtedness to consolidated EBITDDA										3.75
Opco [Member] | Fiscal Quarter Ending on or After June 30, 2017 [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Ratio of consolidated indebtedness to consolidated EBITDDA										3.5
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]
Repayment of principal amount						$ 10,000,000
Revolving credit facility current borrowing base		$ 105,000,000
Weighted average interest rate						2.63%		1.90%		2.52%	1.90%
Write off of debt issuance costs		600,000
Borrowings outstanding	100,000,000					$ 100,000,000	$ 110,000,000			$ 100,000,000
Term of credit facility				5 years
Senior secured revolving credit facility				$ 100,000,000
Revolving credit facility borrowing base	137,000,000	$ 137,000,000				137,000,000				$ 137,000,000
Revolving credit facility maturity period										2019-11
NRP Oil and Gas [Member] | Amended on November 2014 [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Revolving credit facility borrowing base	$ 500,000,000					$ 500,000,000				$ 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										0.375%

Debt and Debt-Affiliate - Debt

Debt and Debt-Affiliate - Debt (Detail) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014	Oct. 31, 2014	Sep. 30, 2013
Debt Instrument [Line Items]
Total debt	$ 1,432,118	$ 1,475,223
Less: current portion of long-term debt, net	(155,983)	(80,983)
Total long-term debt and debt - affiliate	1,276,135	1,394,240
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	422,545	422,167
Opco [Member] | $300 Million Floating Rate Revolving Credit Facility, Due October 2017 [Member]
Debt Instrument [Line Items]
Total debt	215,000
Opco [Member] | $300 Million Floating Rate Revolving Credit Facility, Due August 2016 [Member]
Debt Instrument [Line Items]
Total debt		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	13,850	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	21,600	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	$ 100,000	$ 110,000

Debt and Debt-Affiliate - Deb47

Debt and Debt-Affiliate - Debt (Parenthetical) (Detail) - Jun. 30, 2015 - USD ($) $ in Millions	Total
NRP LP [Member] | 9.125% Senior Notes, with Semi-annual Interest Payments in April and October, Maturing October 2018 [Member]
Debt Instrument [Line Items]
Senior Notes, Face amount	$ 425
Rate of senior notes	9.125%
Opco [Member] | $300 Million Floating Rate Revolving Credit Facility, Due October 2017 [Member]
Debt Instrument [Line Items]
Floating rate revolving credit facility	$ 300
Opco [Member] | $300 Million Floating Rate Revolving Credit Facility, Due August 2016 [Member]
Debt Instrument [Line Items]
Floating rate revolving credit facility	300
Opco [Member] | $200 Million Floating Rate Term Loan, Due January 2016 [Member]
Debt Instrument [Line Items]
Floating rate revolving credit facility	$ 200
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]
Rate of senior notes	4.91%
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]
Rate of senior notes	8.38%
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]
Rate of senior notes	5.05%
Opco [Member] | 5.31% Utility Local Improvement Obligation, with Annual Principal and Interest Payments, Maturing in March 2021 [Member]
Debt Instrument [Line Items]
Rate of senior notes	5.31%
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]
Rate of senior notes	5.55%
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]
Rate of senior notes	4.73%
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]
Rate of senior notes	5.82%
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]
Rate of senior notes	8.92%
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]
Rate of senior notes	5.03%
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]
Rate of senior notes	5.18%
Senior Notes Issued at 99.007% [Member] | NRP LP [Member] | 9.125% Senior Notes, with Semi-annual Interest Payments in April and October, Maturing October 2018 [Member]
Debt Instrument [Line Items]
Floating rate revolving credit facility	$ 300
Senior Notes issue percentage	99.007%
Senior Notes Issued at 99.5% [Member] | NRP LP [Member] | 9.125% Senior Notes, with Semi-annual Interest Payments in April and October, Maturing October 2018 [Member]
Debt Instrument [Line Items]
Floating rate revolving credit facility	$ 125
Senior Notes issue percentage	99.50%

Fair Value Measurements - Sched

Fair Value Measurements - Schedule of Carrying Amount and Estimated Fair Value of Other Financial Instruments (Detail) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying Amount	$ 4,833	$ 4,870
Estimated fair value	5,174	5,162
NRP LP Senior Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying Amount	422,545	422,167
Estimated fair value	372,406	423,780
Opco Senior Notes and Utility Local Improvement Obligation [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying Amount	619,573	668,056
Estimated fair value	542,901	672,740
Opco Revolving Credit Facility and Term Loan Facility [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying Amount	290,000	275,000
Estimated fair value	290,000	275,000
NRP Oil and Gas Revolving Credit Facility [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying Amount	100,000	110,000
Estimated fair value	$ 100,000	$ 110,000

Fair value Measurements - Addit

Fair value Measurements - Additional Information (Detail) - USD ($) $ in Thousands	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014
Fair Value Measurements Disclosure [Line Items]
Estimated fair value	$ 5,174		$ 5,162
NRP LP Senior Notes [Member]
Fair Value Measurements Disclosure [Line Items]
Estimated fair value		$ 378,300
NRP LP Senior Notes [Member] | Scenario, Previously Reported [Member]
Fair Value Measurements Disclosure [Line Items]
Estimated fair value		417,000
Opco Senior Notes and Utility Local Improvement Obligation [Member]
Fair Value Measurements Disclosure [Line Items]
Estimated fair value		557,900
Opco Senior Notes and Utility Local Improvement Obligation [Member] | Scenario, Previously Reported [Member]
Fair Value Measurements Disclosure [Line Items]
Estimated fair value		$ 629,500

Related Party Transactions - Ad

Related Party Transactions - Additional Information (Detail) - USD ($) shares in Thousands, $ in Thousands	1 Months Ended		3 Months Ended		6 Months Ended
	Apr. 30, 2015	Oct. 31, 2014	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Related Party Transaction [Line Items]
Accounts payable - affiliates			$ 939		$ 939		$ 950
Lease expenses			200	$ 300	200	$ 300
Total revenues and other income			137,630	90,561	247,307	170,870
Unrecouped minimum royalty payments			87,116		87,116		87,053
Accounts receivable - affiliate			8,192		8,192		9,494
Gain on reserve swaps	$ 9,300
Senior Notes Due 2018 [Member] | Cline Trust Company, LLC [Member]
Related Party Transaction [Line Items]
Partnership common units owned		5,350
Principal amount of partnership purchased		$ 20,000
Rate of senior notes		9.125%
Aggregate principal amount of senior notes		$ 125,000
Senior notes due			19,900		19,900
Western Pocahontas Properties Limited Partnership [Member]
Related Party Transaction [Line Items]
Coal related expenses-affiliates			100		100
Quintana Minerals [Member]
Related Party Transaction [Line Items]
Accounts payable - affiliates			600		600		600
Western Pocahontas Properties [Member]
Related Party Transaction [Line Items]
Accounts payable - affiliates			300		$ 300		400
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
Unrecouped minimum royalty payments			86,800		$ 86,800
Net amount receivable			4,800		4,800		5,600
Accounts receivable - affiliate			400		400		1,100
Foresight Energy LP [Member]
Related Party Transaction [Line Items]
Accounts receivable-affiliates			8,200		8,200		9,200
Foresight Energy LP [Member] | Coal Sales [Member]
Related Party Transaction [Line Items]
Total revenues and other income			31,600	20,400	49,900	38,300
Sugar Camp [Member]
Related Party Transaction [Line Items]
Aggregate payments remaining under the lease			83,800		83,800		86,300
Unearned income			37,100		37,100		39,000
Net amount receivable			46,700		46,700		47,300
Accounts receivable - affiliate			1,900		1,900		1,800
Corsa [Member]
Related Party Transaction [Line Items]
Unrecouped minimum royalty payments			300		300
Accounts receivable - affiliate			200		200		$ 300
Coal royalty revenues			$ 800	$ 700	$ 1,500	$ 1,600

Related Party Transactions - Su

Related Party Transactions - Summary of Reimbursements (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Related Party Transaction [Line Items]
Reimbursement for services	$ 3,535	$ 3,000	$ 7,321	$ 6,094
Western Pocahontas Properties and Quintana Minerals Corporation [Member]
Related Party Transaction [Line Items]
Reimbursement for services	$ 3,535	$ 3,000	$ 7,321	$ 6,094

Major Lessees - Revenues from L

Major Lessees - Revenues from Lessees that Exceeded Ten Percent of Total Revenues and Other Income (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Foresight Energy and Affiliates [Member]
Operating Leased Assets [Line Items]
Revenues	$ 31,581	$ 20,432	$ 49,879	$ 38,254
Percent	23.00%	23.00%	20.00%	22.00%
Alpha Natural Resources [Member]
Operating Leased Assets [Line Items]
Revenues	$ 8,943	$ 12,810	$ 17,772	$ 24,451
Percent	6.00%	14.00%	7.00%	14.00%

Major Lessees - Additional Info

Major Lessees - Additional Information (Detail)	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Williamson [Member]
Operating Leased Assets [Line Items]
Percentage of revenues and other income received from major lessee excluding reserve swap	12.00%	10.00%	9.00%	11.00%

Long-Term Incentive Plans - Sum

Long-Term Incentive Plans - Summary of Activity in Outstanding Grants (Detail) - Jun. 30, 2015 - shares	Total
Compensation and Retirement Disclosure [Abstract]
Outstanding grants at the beginning of the period	1,153,393
Grants during the period	498,486
Grants vested and paid during the period	(290,430)
Forfeitures during the period	(23,875)
Outstanding grants at the end of the period	1,337,574

Long-Term Incentive Plans - Add

Long-Term Incentive Plans - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period of Grants in years			4 years
Risk free interest rate, minimum			0.31%
Risk free interest rate, maximum			1.35%
Volatility rate, minimum			39.41%
Volatility rate, maximum			53.35%
Partnership's historical distribution rate	7.60%		7.60%
Partnership's historical forfeiture rate	4.97%		4.97%
Expenses related to Incentive Plan to be reimbursed to general partner			$ 4.4	$ 5.3
Unaccrued cost associated with outstanding grants and related DERs	$ 3.2	$ 9.4	3.2	9.4
General Partner [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Payments made in connection with Long-Term Incentive Plan	$ 1.4	$ 1.5	$ 1.5	$ 0.4

Distributions - Additional Info

Distributions - Additional Information (Detail) - $ / shares	May. 14, 2015	Feb. 13, 2015	May. 14, 2014	Jan. 31, 2014
Equity [Abstract]
Quarterly distribution to holders of common units	$ 0.09	$ 0.35	$ 0.35	$ 0.35

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Jun. 30, 2015	Apr. 30, 2015
OCI Wyoming [Member]
Commitments And Contingencies [Line Items]
Contingent consideration accrued			$ 8.8
Anadarko Holding Company [Member]
Commitments And Contingencies [Line Items]
Contingent consideration accrued				$ 8.8
Net present value payable of contingent consideration under the agreement				$ 50
Anadarko Holding Company [Member] | OCI Wyoming [Member]
Commitments And Contingencies [Line Items]
Contingent consideration paid	$ 0.5	$ 3.8

Subsequent Events - Additional

Subsequent Events - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	Jul. 21, 2015	May. 14, 2015	Feb. 13, 2015	May. 14, 2014	Jan. 31, 2014	Jul. 31, 2015	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Subsequent Event [Line Items]
Distributions per unit declared		$ 0.09	$ 0.35	$ 0.35	$ 0.35
Foresight Energy LP [Member]
Subsequent Event [Line Items]
Royalty revenues							$ 4,400
Alpha Natural Resources [Member]
Subsequent Event [Line Items]
Revenues from affiliates							$ 8,943	$ 12,810	$ 17,772	$ 24,451
Revenue from affiliates, percentage							6.50%
Pre-petition amount for royalties due from affiliates							$ 2,500
Subsequent Event [Member]
Subsequent Event [Line Items]
Distributions per unit declared	$ 0.09
Subsequent Event [Member] | Foresight Energy LP [Member]
Subsequent Event [Line Items]
Cash impact of failure to make deficiency payment						$ 3,100