Black Stone Minerals (BSM) 10-Q 5 Nov 19 2019 Q3 Quarterly report Financial data

Cover

Cover - shares	9 Months Ended
	Sep. 30, 2019	Oct. 30, 2019
Entity Information [Line Items]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2019
Document Transition Report	false
Entity File Number	001-37362
Entity Registrant Name	Black Stone Minerals, L.P.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	47-1846692
Entity Address, Address Line One	1001 Fannin Street, Suite 2020
Entity Address, City or Town	Houston,
Entity Address, State or Province	TX
Entity Address, Postal Zip Code	77002
City Area Code	(713)
Local Phone Number	445-3200
Title of 12(b) Security	Common Units Representing Limited Partner Interests
Trading Symbol	BSM
Security Exchange Name	NYSE
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Smaller reporting company	false
Emerging growth company	false
Entity shell company	false
Amendment Flag	false
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q3
Entity Central Index Key	0001621434
Current Fiscal Year End Date	--12-31
Common Units
Entity Information [Line Items]
Entity Partnership Units Outstanding (in shares)		205,959,790
Preferred Units
Entity Information [Line Items]
Entity Partnership Units Outstanding (in shares)		14,711,219

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
CURRENT ASSETS
Cash and cash equivalents	$ 1,966	$ 5,414
Accounts receivable	84,842	113,148
Commodity derivative assets	33,054	37,970
Prepaid expenses and other current assets	1,472	1,001
TOTAL CURRENT ASSETS	121,334	157,533
PROPERTY AND EQUIPMENT
Oil and natural gas properties, at cost, using the successful efforts method of accounting, includes unproved properties of $1,091,244 and $1,063,883 at September 30, 2019 and December 31, 2018, respectively	3,403,485	3,441,188
Accumulated depreciation, depletion, amortization, and impairment	(1,948,866)	(1,865,692)
Oil and natural gas properties, net	1,454,619	1,575,496
Other property and equipment, net of accumulated depreciation of $11,450 and $11,048 at September 30, 2019 and December 31, 2018, respectively	2,435	385
NET PROPERTY AND EQUIPMENT	1,457,054	1,575,881
DEFERRED CHARGES AND OTHER LONG-TERM ASSETS	17,425	16,710
TOTAL ASSETS	1,595,813	1,750,124
CURRENT LIABILITIES
Accounts payable	4,574	4,149
Accrued liabilities	17,384	60,089
Other current liabilities	1,058	528
TOTAL CURRENT LIABILITIES	23,016	64,766
LONG–TERM LIABILITIES
Credit facility	413,000	410,000
Accrued incentive compensation	1,750	1,813
Commodity derivative liabilities	0	0
Asset retirement obligations	15,584	14,948
Other long-term liabilities	6,781	55,973
TOTAL LIABILITIES	460,131	547,500
COMMITMENTS AND CONTINGENCIES (Note 8)
EQUITY
Partners' equity – general partner interest	0	0
TOTAL EQUITY	837,321	904,263
TOTAL LIABILITIES, MEZZANINE EQUITY, AND EQUITY	1,595,813	1,750,124
Series B Cumulative Convertible Preferred Units
MEZZANINE EQUITY
Partners' equity – convertible preferred units	298,361	298,361
Common Units
EQUITY
Partners' equity - units	837,321	714,823
Subordinated Units
EQUITY
Partners' equity - units	$ 0	$ 189,440

CONSOLIDATED BALANCE SHEETS (Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) shares in Thousands, $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Unproved properties	$ 1,091,660	$ 1,063,883
Accumulated depreciation	$ 11,450	$ 11,048
Series B Cumulative Convertible Preferred Units
Partners' equity, preferred units, outstanding (in shares)	14,711	14,711
Common Units
Partners' equity - units, outstanding (in shares)	205,952	108,363
Subordinated Units
Partners' equity - units, outstanding (in shares)	0	96,329

CONSOLIDATED STATEMENTS OF OPER

CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
REVENUE
Revenue from contracts with customers	$ 113,079	$ 158,232	$ 372,499	$ 431,715
Gain (loss) on commodity derivative instruments	24,290	(18,514)	12,294	(68,194)
TOTAL REVENUE	137,369	139,718	384,793	363,521
OPERATING (INCOME) EXPENSE
Lease operating expense	4,356	4,229	13,497	12,767
Production costs and ad valorem taxes	15,877	17,641	44,919	46,939
Exploration expense	64	34	372	6,782
Depreciation, depletion, and amortization	27,375	29,273	84,933	88,135
General and administrative	14,189	22,083	49,750	60,416
Accretion of asset retirement obligations	275	278	829	820
(Gain) loss on sale of assets, net	0	0	0	(2)
TOTAL OPERATING EXPENSE	62,136	73,538	194,300	215,857
INCOME (LOSS) FROM OPERATIONS	75,233	66,180	190,493	147,664
OTHER INCOME (EXPENSE)
Interest and investment income	44	53	137	123
Interest expense	(5,395)	(5,518)	(16,572)	(15,319)
Other income (expense)	365	60	293	(1,046)
TOTAL OTHER EXPENSE	(4,986)	(5,405)	(16,142)	(16,242)
NET INCOME (LOSS)	70,247	60,775	174,351	131,422
Net (income) loss attributable to noncontrolling interests	0	(22)	0	(1)
Distributions on Series A redeemable preferred units	0	0	0	(25)
Distributions on Series B cumulative convertible preferred units	(5,250)	(5,250)	(15,750)	(15,750)
NET INCOME (LOSS) ATTRIBUTABLE TO THE GENERAL PARTNER AND COMMON AND SUBORDINATED UNITS	64,997	55,503	158,601	115,646
ALLOCATION OF NET INCOME (LOSS):
General partner interest	0	0	0	0
NET INCOME (LOSS) ATTRIBUTABLE TO THE GENERAL PARTNER AND COMMON AND SUBORDINATED UNITS	64,997	55,503	158,601	115,646
Common Units
ALLOCATION OF NET INCOME (LOSS):
Allocation of net income (loss)	$ 64,997	$ 29,188	$ 134,608	$ 71,037
NET INCOME (LOSS) ATTRIBUTABLE TO LIMITED PARTNERS PER COMMON AND SUBORDINATED UNIT:
Per unit (basic) (in dollars per share)	$ 0.32	$ 0.27	$ 0.87	$ 0.67
Weighted average units outstanding (basic) (in shares)	205,957	106,706	155,513	105,254
Per unit (diluted) (in dollars per share)	$ 0.32	$ 0.27	$ 0.87	$ 0.67
Weighted average units outstanding (diluted) (in shares)	205,957	106,706	155,513	105,254
Subordinated Units
ALLOCATION OF NET INCOME (LOSS):
Allocation of net income (loss)	$ 0	$ 26,315	$ 23,993	$ 44,609
NET INCOME (LOSS) ATTRIBUTABLE TO LIMITED PARTNERS PER COMMON AND SUBORDINATED UNIT:
Per unit (basic) (in dollars per share)	$ 0	$ 0.27	$ 0.48	$ 0.46
Weighted average units outstanding (basic) (in shares)	0	96,329	50,458	96,021
Per unit (diluted) (in dollars per share)	$ 0	$ 0.27	$ 0.48	$ 0.46
Weighted average units outstanding (diluted) (in shares)	0	96,329	50,458	96,021
Oil and condensate sales
REVENUE
Revenue from contracts with customers	$ 68,255	$ 82,712	$ 200,031	$ 232,920
Natural gas and natural gas liquids sales
REVENUE
Revenue from contracts with customers	41,340	63,080	156,622	170,179
Lease bonus and other income
REVENUE
Revenue from contracts with customers	$ 3,484	$ 12,440	$ 15,846	$ 28,616

CONSOLIDATED STATEMENTS OF EQUI

CONSOLIDATED STATEMENTS OF EQUITY - USD ($) shares in Thousands, $ in Thousands		Total	Non-Controlling Interests	Common Units	Subordinated Units	Partners' equity — common units	Partners' equity — subordinated units	Series B cumulative convertible preferred units on an as-converted basis	Series B cumulative convertible preferred units on an as-converted basisPartners' equity — common units	Series A redeemable preferred units on an as-converted basis	Series A redeemable preferred units on an as-converted basisPartners' equity — common units	Series A redeemable preferred units on an as-converted basisPartners' equity — subordinated units
Beginning balance (in shares) at Dec. 31, 2017				103,456	95,388
Beginning balance at Dec. 31, 2017		$ 768,121	$ 867			$ 603,116	$ 164,138
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Repurchases of common and subordinated units (in shares)				(451)	(23)
Repurchases of common and subordinated units		(8,441)				(8,099)	(342)
Issuance of common units, net of offering costs (in shares)				8
Issuance of common units, net of offering costs		138				138
Restricted units granted, net of forfeitures (in shares)				1,177
Equity–based compensation	[1]	18,294				18,075	219
Distributions		(52,545)	(52)			(32,581)	(19,912)
Charges to partners' equity for accrued distribution equivalent rights		(661)				(661)
Distributions on preferred units								$ (5,250)	$ (5,250)	$ (25)	$ (13)	$ (12)
Net income (loss)		41,957	27			29,592	12,338
Conversion of subordinated units ( in shares)				736	964
Conversion of subordinated units		24,248				10,498	13,750
Ending balance (in shares) at Mar. 31, 2018				104,926	96,329
Ending balance at Mar. 31, 2018		785,836	842			614,815	170,179
Beginning balance (in shares) at Dec. 31, 2017				103,456	95,388
Beginning balance at Dec. 31, 2017		768,121	867			603,116	164,138
Ending balance (in shares) at Dec. 31, 2018				108,363	96,329
Ending balance at Dec. 31, 2018		904,263				714,823	189,440
Beginning balance (in shares) at Mar. 31, 2018				104,926	96,329
Beginning balance at Mar. 31, 2018		785,836	842			614,815	170,179
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Repurchases of common and subordinated units (in shares)				(35)
Repurchases of common and subordinated units		(630)				(630)
Issuance of common units, net of offering costs (in shares)				509
Issuance of common units, net of offering costs		8,929				8,929
Restricted units granted, net of forfeitures (in shares)				94
Equity–based compensation	[1]	8,521				8,521
Distributions		(53,182)	(62)			(33,011)	(20,109)
Charges to partners' equity for accrued distribution equivalent rights		(643)				(643)
Distributions on preferred units								(5,250)	(5,250)
Net income (loss)		28,690	(49)			22,798	5,941
Ending balance (in shares) at Jun. 30, 2018				105,494	96,329
Ending balance at Jun. 30, 2018		772,271	731			615,529	156,011
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common units, net of offering costs (in shares)				1,604
Issuance of common units, net of offering costs		29,302				29,302
Issuance of common units for property acquisitions (in shares)				1,227
Issuance of common units for property acquisitions		22,530				22,530
Restricted units granted, net of forfeitures (in shares)				5
Equity–based compensation	[1]	8,991				8,991	0
Distributions		(68,610)	(47)			(36,052)	(32,511)
Charges to partners' equity for accrued distribution equivalent rights		(1,061)				(1,061)
Distributions on preferred units								(5,250)	(5,250)
Net income (loss)		60,775	23			34,410	26,342
Ending balance (in shares) at Sep. 30, 2018				108,330	96,329
Ending balance at Sep. 30, 2018		818,948	$ 707			668,399	149,842
Beginning balance (in shares) at Dec. 31, 2018				108,363	96,329
Beginning balance at Dec. 31, 2018		904,263				714,823	189,440
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Repurchases of common and subordinated units (in shares)				(588)
Repurchases of common and subordinated units		(10,110)				(10,110)
Issuance of common units, net of offering costs		(43)				(43)
Issuance of common units for property acquisitions (in shares)				57
Issuance of common units for property acquisitions		943				943
Restricted units granted, net of forfeitures (in shares)				1,545
Equity–based compensation		13,669				13,669
Distributions		(75,917)				(40,275)	(35,642)
Charges to partners' equity for accrued distribution equivalent rights		(1,044)				(1,044)
Distributions on preferred units								(5,250)	(5,250)
Net income (loss)		9,017				7,155	1,862
Ending balance (in shares) at Mar. 31, 2019				109,377	96,329
Ending balance at Mar. 31, 2019		835,528				679,868	155,660
Beginning balance (in shares) at Dec. 31, 2018				108,363	96,329
Beginning balance at Dec. 31, 2018		904,263				714,823	189,440
Ending balance (in shares) at Sep. 30, 2019				205,952	0
Ending balance at Sep. 30, 2019		837,321				837,321	0
Beginning balance (in shares) at Mar. 31, 2019				109,377	96,329
Beginning balance at Mar. 31, 2019		835,528				679,868	155,660
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Repurchases of common and subordinated units (in shares)				(377)
Repurchases of common and subordinated units		(6,164)				(6,164)
Restricted units granted, net of forfeitures (in shares)				627
Equity–based compensation		3,332				3,332
Distributions		(76,113)				(40,471)	(35,642)
Charges to partners' equity for accrued distribution equivalent rights		(766)				(766)
Distributions on preferred units								(5,250)	(5,250)
Net income (loss)		95,087				72,956	22,131
Conversion of subordinated units ( in shares)				96,329	(96,329)
Conversion of subordinated units						142,149	(142,149)
Ending balance (in shares) at Jun. 30, 2019				205,956	0
Ending balance at Jun. 30, 2019		845,654				845,654	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Restricted units granted, net of forfeitures (in shares)				(4)
Equity–based compensation		3,385				3,385
Distributions		(76,204)				(76,204)
Charges to partners' equity for accrued distribution equivalent rights		(511)				(511)
Distributions on preferred units								$ (5,250)	$ (5,250)
Net income (loss)		70,247				70,247
Ending balance (in shares) at Sep. 30, 2019				205,952	0
Ending balance at Sep. 30, 2019		$ 837,321				$ 837,321	$ 0
[1]	The change in Partners' equity for equity-based compensation during the nine-month period ended September 30, 2018 was incorrectly allocated between Partners' equity - common units and Partners' equity - subordinated units in the Partnership's prior reports. The Partnership concluded that this error was not material to any of the prior reporting periods. As such, the revision for this correction has been made to the prior periods presented.

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
CASH FLOWS FROM OPERATING ACTIVITIES
Net income (loss)	$ 174,351	$ 131,422
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation, depletion, and amortization	84,933	88,135
Accretion of asset retirement obligations	829	820
Amortization of deferred charges	779	653
(Gain) loss on commodity derivative instruments	(12,294)	68,194
Net cash (paid) received on settlement of commodity derivative instruments	18,320	(20,461)
Equity-based compensation	16,906	24,947
Exploratory dry hole expense	3	6,784
Deferred rent		802
(Gain) loss on sale of assets, net	0	(2)
Changes in operating assets and liabilities:
Accounts receivable	28,454	(29,989)
Prepaid expenses and other current assets	(471)	7
Accounts payable, accrued liabilities, and other	(5,172)	18,515
Settlement of asset retirement obligations	(328)	(108)
NET CASH PROVIDED BY OPERATING ACTIVITIES	306,310	289,719
CASH FLOWS FROM INVESTING ACTIVITIES
Acquisitions of oil and natural gas properties	(42,969)	(106,390)
Additions to oil and natural gas properties	(63,606)	(119,676)
Additions to oil and natural gas properties leasehold costs	(933)	(4,639)
Purchases of other property and equipment	(2,452)	(15)
Proceeds from the sale of oil and natural gas properties	550	8,390
Proceeds from farmouts of oil and natural gas properties	60,577	78,605
NET CASH USED IN INVESTING ACTIVITIES	(48,833)	(143,725)
CASH FLOWS FROM FINANCING ACTIVITIES
Proceeds from issuance of common units, net of offering costs	(43)	38,369
Distributions to noncontrolling interests	0	(161)
Distribution equivalents paid	(2,982)	0
Redemptions of Series A redeemable preferred units	0	(2,115)
Borrowings under credit facility	252,500	264,500
Repayments under credit facility	(249,500)	(250,500)
Debt issuance costs and other	0	(754)
NET CASH USED IN FINANCING ACTIVITIES	(260,925)	(147,195)
NET CHANGE IN CASH AND CASH EQUIVALENTS	(3,448)	(1,201)
CASH AND CASH EQUIVALENTS – beginning of the period	5,414	5,642
CASH AND CASH EQUIVALENTS – end of the period	1,966	4,441
SUPPLEMENTAL DISCLOSURE
Interest paid	15,854	14,607
Common and Subordinated Units
CASH FLOWS FROM FINANCING ACTIVITIES
Distributions to unitholders	(228,234)	(174,348)
Repurchases of common and subordinated units	(16,916)	(9,071)
Preferred Units
CASH FLOWS FROM FINANCING ACTIVITIES
Distributions to unitholders	0	(690)
Series B cumulative convertible preferred units on an as-converted basis | Preferred Units
CASH FLOWS FROM FINANCING ACTIVITIES
Distributions to unitholders	$ (15,750)	$ (12,425)

Earnings Per Unit

Earnings Per Unit	9 Months Ended
	Sep. 30, 2019
Earnings Per Share [Abstract]
Earnings Per Unit	EARNINGS PER UNIT The Partnership applies the two-class method for purposes of calculating earnings per unit (“EPU”). The holders of the Partnership’s restricted common units have all the rights of a unitholder, including non-forfeitable distribution rights. As participating securities, the restricted common units are included in the calculation of basic earnings per unit. For the periods presented, the amount of earnings allocated to these participating units was not material. Net income (loss) attributable to the Partnership is allocated to the Partnership’s general partner and the common and subordinated unitholders in proportion to their pro rata ownership after giving effect to distributions, if any, declared during the period. The Partnership assesses the Series B cumulative convertible preferred units on an as-converted basis for the purpose of calculating diluted EPU. For the three and nine months ended September 30, 2019 and 2018, there were no common units related to the Partnership's Series B cumulative convertible preferred units included in the calculation of diluted EPU. The Partnership’s restricted performance unit awards are contingently issuable units that are considered in the calculation of diluted EPU. The Partnership assesses the number of units that would be issuable, if any, under the terms of the arrangement if the end of the reporting period were the end of the contingency period. For the three and nine months ended September 30, 2019 and 2018, there were no units related to the Partnership’s restricted performance unit awards included in the calculation of diluted EPU. The following table sets forth the computation of basic and diluted earnings per common and subordinated unit: Three Months Ended Nine Months Ended 2019 2018 2019 2018 (in thousands, except per unit amounts) NET INCOME (LOSS) $ 70,247 $ 60,775 $ 174,351 $ 131,422 Net (income) loss attributable to noncontrolling interests — (22) — (1) Distributions on Series A redeemable preferred units — — — (25) Distributions on Series B cumulative convertible preferred units (5,250) (5,250) (15,750) (15,750) NET INCOME (LOSS) ATTRIBUTABLE TO THE GENERAL PARTNER AND COMMON AND SUBORDINATED UNITS 64,997 55,503 158,601 115,646 ALLOCATION OF NET INCOME (LOSS): General partner interest $ — $ — $ — $ — Common units 64,997 29,188 134,608 71,037 Subordinated units — 26,315 23,993 44,609 $ 64,997 $ 55,503 $ 158,601 $ 115,646 Weighted average common units outstanding: Weighted average common units outstanding (basic) 205,957 106,706 155,513 105,254 Effect of dilutive securities — — — — Weighted average common units outstanding (diluted) 205,957 106,706 155,513 105,254 Weighted average subordinated units outstanding: Weighted average subordinated units outstanding (basic) — 96,329 50,458 96,021 Effect of dilutive securities — — — — Weighted average subordinated units outstanding (diluted) — 96,329 50,458 96,021 NET INCOME (LOSS) ATTRIBUTABLE TO LIMITED PARTNERS PER COMMON AND SUBORDINATED UNIT: Per common unit (basic) $ 0.32 $ 0.27 $ 0.87 $ 0.67 Per subordinated unit (basic) — 0.27 0.48 0.46 Per common unit (diluted) 0.32 0.27 0.87 0.67 Per subordinated unit (diluted) — 0.27 0.48 0.46 The following units of potentially dilutive securities were excluded from the computation of diluted weighted average units outstanding because their inclusion would be anti-dilutive: Three Months Ended Nine Months Ended 2019 2018 2019 2018 (in thousands) Potentially dilutive securities (common units): Series A redeemable preferred units on an as-converted basis — — — 189 Series B cumulative convertible preferred units on an as-converted basis 14,969 14,969 14,969 14,969 14,969 14,969 14,969 15,158 Potentially dilutive securities (subordinated units): Series A redeemable preferred units on an as-converted basis — — — 247

Subsequent Events

Subsequent Events	9 Months Ended
	Sep. 30, 2019
Subsequent Events [Abstract]
Subsequent Events	SUBSEQUENT EVENTS    On October 23, 2019, the Board approved a distribution for the three months ended September 30, 2019 of $0.37 per common unit. Distributions will be payable on November 21, 2019 to unitholders of record at the close of business on November 14, 2019.

Business and Basis of Presentat

Business and Basis of Presentation	9 Months Ended
	Sep. 30, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Business and Basis of Presentation	BUSINESS AND BASIS OF PRESENTATION Description of the Business Black Stone Minerals, L.P. (“BSM” or the “Partnership”) is a publicly traded Delaware limited partnership that owns oil and natural gas mineral interests, which make up the vast majority of the asset base. The Partnership's assets also include nonparticipating royalty interests and overriding royalty interests. These interests, which are substantially non-cost-bearing, are collectively referred to as “mineral and royalty interests.” The Partnership’s mineral and royalty interests are located in 41 states in the continental United States, including all of the major onshore producing basins. The Partnership also owns non-operated working interests in certain oil and natural gas properties. The Partnership's common units trade on the New York Stock Exchange under the symbol "BSM." Basis of Presentation The accompanying unaudited interim consolidated financial statements of the Partnership have been prepared in accordance with generally accepted accounting principles ("GAAP") in the United States and pursuant to the rules and regulations of the U.S. Securities and Exchange Commission (“SEC”). These unaudited interim consolidated financial statements have been prepared in accordance with the instructions to Form 10-Q and, therefore, do not include all disclosures required for financial statements prepared in conformity with GAAP. Accordingly, the accompanying unaudited interim consolidated financial statements and related notes should be read in conjunction with the Partnership’s consolidated financial statements included in the Partnership’s Annual Report on Form 10-K for the year ended December 31, 2018 ("2018 Annual Report on Form 10-K"). The unaudited interim consolidated financial statements include the consolidated results of the Partnership. The results of operations for the nine months ended September 30, 2019 are not necessarily indicative of the results to be expected for the full year. In the opinion of management, all adjustments, which are of a normal and recurring nature, necessary for the fair presentation of the financial results for all periods presented have been reflected. All intercompany balances and transactions have been eliminated. The Partnership evaluates the significant terms of its investments to determine the method of accounting to be applied to each respective investment. Investments in which the Partnership has less than a 20% ownership interest and does not have control or exercise significant influence are accounted for using fair value or cost minus impairment if fair value is not readily determinable. Investments in which the Partnership exercises control are consolidated, and the noncontrolling interests of such investments, which are not attributable directly or indirectly to the Partnership, are presented as a separate component of net income (loss) and equity in the accompanying unaudited interim consolidated financial statements. The unaudited interim consolidated financial statements include undivided interests in oil and natural gas property rights. The Partnership accounts for its share of oil and natural gas property rights by reporting its proportionate share of assets, liabilities, revenues, costs, and cash flows within the relevant lines on the accompanying unaudited interim consolidated balance sheets, statements of operations, and statements of cash flows. Segment Reporting The Partnership operates in a single operating and reportable segment. Operating segments are defined as components of an enterprise for which separate financial information is evaluated regularly by the chief operating decision maker in deciding how to allocate resources and assess performance. The Partnership’s chief executive officer has been determined to be the chief operating decision maker and allocates resources and assesses performance based upon financial information at the consolidated level.

Summary of Significant Accounti

Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2019
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Significant Accounting Policies Significant accounting policies are disclosed in the Partnership’s 2018 Annual Report on Form 10-K. There have been no changes in such policies or the application of such policies during the nine months ended September 30, 2019, with the exception of ASC 842, as defined below. Accounts Receivable The following table presents information about the Partnership's accounts receivable: September 30, 2019 December 31, 2018 (in thousands) Accounts receivable: Revenues from contracts with customers $ 77,837 $ 107,804 Other 7,005 5,344 Total accounts receivable $ 84,842 $ 113,148 Recent Accounting Pronouncements In February 2016, the Financial Accounting Standards Board ("FASB") issued Accounting Standards Update ("ASU") 2016-02, Leases (Topic 842) ("ASC 842"), that supersedes Accounting Standards Codification ("ASC") 840, Leases by requiring lessees to recognize lease assets and lease liabilities classified as operating leases on the balance sheet. See Note 3 - Impact of ASC 842 Adoption for further details related to the Partnership's adoption of this standard. In August 2018, the FASB issued ASU 2018-13, Fair Value Measurement (Topic 820)

Impact of ASC 842 Adoption

Impact of ASC 842 Adoption	9 Months Ended
	Sep. 30, 2019
Leases [Abstract]
Impact of ASC 606 Adoption	IMPACT OF ASC 842 ADOPTION Leases On January 1, 2019, the Partnership adopted ASC 842 using the modified retrospective method. ASC 842 requires the recognition of lease assets and lease liabilities by lessees for those leases classified as operating leases under the previous guidance. The Partnership used January 1, 2019, the beginning of the period of adoption, as its date of initial application. The Partnership elected the package of practical expedients upon transition which will retain the lease classification for leases and any unamortized initial direct costs that existed prior to the adoption of the standard. The adoption of the standard resulted in the recognition of operating lease right-of-use (“ROU”) assets and operating lease liabilities on the consolidated balance sheet as of January 1, 2019. ROU assets and operating lease liabilities were less than 1% of the Partnership's total assets as of September 30, 2019 and were not considered material to the Partnership. There was no related impact on the consolidated statement of operations. The standard had no impact on the Partnership’s debt covenant compliance under existing agreements. The Partnership determines if an arrangement is a lease at inception by considering whether (1) explicitly or implicitly identified assets have been deployed in the agreement and (2) the Partnership obtains substantially all of the economic benefits from the use of that underlying asset and directs how and for what purpose the asset is used during the term of the agreement. Operating leases are included in Deferred charges and other long-term assets, Other current liabilities, and Other long-term liabilities in the consolidated balance sheets. As of September 30, 2019, none of the Partnership’s leases were classified as financing leases. ROU assets represent the Partnership’s right to use an underlying asset for the lease term and operating lease liabilities represent the Partnership’s obligation to make lease payments arising from the lease. ROU assets are recognized at commencement date and consist of the present value of remaining lease payments over the lease term, initial direct costs, prepaid lease payments less any lease incentives. Operating lease liabilities are recognized at commencement date based on the present value of remaining lease payments over the lease term. The Partnership uses the implicit rate, when readily determinable, or its incremental borrowing rate based on the information available at commencement date to determine the present value of lease payments. The lease terms may include periods covered by options to extend the lease when it is reasonably certain that the Partnership will exercise that option and periods covered by options to terminate the lease when it is not reasonably certain that the Partnership will exercise that option. Lease expense for lease payments is recognized on a straight-line basis over the lease term. The Partnership made an accounting policy election to not recognize leases with terms of less than twelve months on the consolidated balance sheets and recognize those lease payments in the consolidated statements of operations on a straight-line basis over the lease term. In the event that the Partnership’s assumptions and expectations change, it may have to revise its ROU assets and operating lease liabilities.

Oil and Natural Gas Properties

Oil and Natural Gas Properties	9 Months Ended
	Sep. 30, 2019
Business Combinations [Abstract]
Oil and Natural Gas Properties	OIL AND NATURAL GAS PROPERTIES Acquisitions of proved oil and natural gas properties and working interests are generally considered business combinations and are recorded at their estimated fair value as of the acquisition date. Acquisitions that consist of all or substantially all unproved oil and natural gas properties are generally considered asset acquisitions and are recorded at cost. 2019 Acquisitions During the nine months ended September 30, 2019, the Partnership closed on multiple acquisitions of mineral and royalty interests for total consideration of $43.9 million. Acquisitions that were considered business combinations were primarily located in the Permian Basin. These acquisitions were funded with borrowings under the Credit Facility (as defined in Note 7 - Credit Facility) and funds from operating activities. Acquisition related costs of less than $0.1 million were expensed and included in the General and administrative line item of the consolidated statement of operations for the nine months ended September 30, 2019. The following table summarizes these acquisitions which were considered business combinations: Assets Acquired Consideration Paid Proved Unproved Net Working Capital Total Fair Value Cash (in thousands) February $ 173 $ 8,437 $ 1 $ 8,611 $ 8,611 March 24 — — 24 24 June 527 3,268 — 3,795 3,795 Total fair value $ 724 $ 11,705 $ 1 $ 12,430 $ 12,430 In addition, during the nine months ended September 30, 2019, the Partnership acquired mineral and royalty interests that consisted of substantially all unproved oil and natural gas properties from various sellers for an aggregate of $31.5 million. These acquisitions were considered asset acquisitions and were primarily located in East Texas and the Permian Basin. The cash portion of the consideration paid for these acquisitions of $30.6 million was funded with borrowings under the Credit Facility and funds from operating activities, and $0.9 million was funded through the issuance of common units of the Partnership based on the fair values of the common units issued on the acquisition dates. 2018 Acquisitions During the year ended December 31, 2018, the Partnership closed on multiple acquisitions of mineral and royalty interests for total consideration of $149.9 million. Acquisitions that were considered business combinations were primarily located in the Permian Basin. The cash portion of the consideration paid for these acquisitions was funded with borrowings under the Credit Facility and funds from operating activities. Acquisition related costs of $0.2 million were expensed and included in the General and administrative line item of the consolidated statement of operations for the year ended December 31, 2018. The following table summarizes these acquisitions which were considered business combinations: Assets Acquired Consideration Paid Proved Unproved Net Working Capital Total Fair Value Cash Fair Value of Common Units Issued (in thousands) March $ 984 $ 21,452 $ 133 $ 22,569 $ 22,569 $ — June 883 13,688 8 14,579 14,579 — July 4,349 7,944 215 12,508 3,764 8,744 August 5,000 34,673 74 39,747 26,461 13,286 September 1,176 — — 1,176 1,176 — November 1,166 — — 1,166 1,166 — Total fair value $ 13,558 $ 77,757 $ 430 $ 91,745 $ 69,715 $ 22,030 In addition, during 2018, the Partnership acquired mineral and royalty interests that consisted of substantially all unproved oil and natural gas properties from various sellers for an aggregate of $58.2 million. These acquisitions were considered asset acquisitions and were primarily located in East Texas and the Permian Basin. The cash portion of the consideration paid for these acquisitions of $57.6 million was funded with borrowings under the Credit Facility and funds from operating activities, and $0.6 million was funded through the issuance of common units of the Partnership based on the fair values of the common units issued on the acquisition dates. During 2018, the Partnership acquired the remaining noncontrolling interest in certain subsidiaries for $1.7 million in cash and merged the subsidiaries into its existing structure. Farmout Agreements In 2017, the Partnership entered into two farmout arrangements designed to reduce its working interest capital expenditures and thereby significantly lower its capital spending other than for royalty and mineral acquisitions. Under these agreements, the Partnership conveyed its rights to participate in certain non-operated working interest opportunities to external capital providers while retaining value from these interests in the form of additional royalty income or retained economic interests. Canaan Farmout On February 21, 2017, the Partnership announced that it had entered into a farmout agreement with Canaan Resource Partners ("Canaan") which covers certain Haynesville and Bossier shale acreage in San Augustine County, Texas operated by XTO Energy Inc., a subsidiary of Exxon Mobil Corporation. The Partnership has an approximate 50% working interest in the acreage and is the largest mineral owner. A total of 20 wells were drilled over an initial phase, beginning with wells spud after January 1, 2017. Canaan elected to participate in an additional phase that began in September 2018 and continues for the lesser of 2 years or until 20 wells have been drilled. After the completion of the second phase, Canaan will have the option to elect to participate in a similar third phase. During the first three phases of the agreement, Canaan commits on a phase-by-phase basis and funds 80% of the Partnership's drilling and completion costs and is assigned 80% of the Partnership's working interests in such wells (40% working interest on an 8/8ths basis) as the wells are drilled. After the third phase, Canaan can earn 40% of the Partnership’s working interest (20% working interest on an 8/8ths basis) in additional wells drilled in the area by continuing to fund 40% of the Partnership's costs for those wells on a well-by-well basis. The Partnership receives an overriding royalty interest (“ORRI”) before payout and an increased ORRI after payout on all wells drilled under the agreement. From the inception of the agreement through September 30, 2019, the Partnership has received $89.7 million from Canaan under the agreement. When working interests in farmout wells are assigned to Canaan, the Partnership's Oil and natural gas properties and Other long-term liabilities are reduced by the reimbursed capital costs. As of September 30, 2019, the Partnership had assigned to Canaan working interests in certain wells drilled and completed, and as such, $0.9 million of the farmout reimbursements received from Canaan are included in the Other long-term liabilities line item of the consolidated balance sheet. Pivotal Farmout On November 21, 2017, the Partnership entered into a farmout agreement with Pivotal Petroleum Partners (“Pivotal”), a portfolio company of Tailwater Capital, LLC. The farmout agreement covers substantially all of the Partnership's remaining working interests under active development in the Shelby Trough area of East Texas, targeting the Haynesville and Bossier shale acreage (after giving effect to the Canaan Farmout), until November 2025. Pivotal will earn the Partnership's remaining working interest in wells operated by XTO Energy Inc. in San Augustine County, Texas not covered by the Canaan Farmout (10% working interest on an 8/8th basis), as well as 100% of the Partnership's working interests (ranging from approximately 12.5% to 25% on an 8/8ths basis) in wells operated by its other major operator in San Augustine and Angelina counties, Texas. Initially, Pivotal is obligated to fund the development of up to 80 wells across several development areas and then has options to continue funding the Partnership's working interest across those areas for the duration of the farmout agreement. Pivotal will fund designated groups of wells. Once Pivotal achieves a specified payout for a designated well group, the Partnership will obtain a majority of the original working interest in such well group. From the inception of the agreement through September 30, 2019, the Partnership received $114.5 million from Pivotal under the agreement. When working interests in farmout wells are assigned to Pivotal, the Partnership's Oil and natural gas properties and Other long-term liabilities are reduced by the reimbursed capital costs. As of September 30, 2019, the Partnership had assigned to Pivotal working interests in certain wells drilled and completed, and as such, $0.4 million of the farmout reimbursements received from Pivotal are included in the Other long-term liabilities line item of the consolidated balance sheet. As of December 31, 2018, $11.6 million and $41.2 million were included in the Other long-term liabilities line item of the consolidated balance sheet related to the farmout agreements with Canaan and Pivotal, respectively.

Commodity Derivative Financial

Commodity Derivative Financial Instruments	9 Months Ended
	Sep. 30, 2019
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Commodity Derivatives And Financial Instruments	COMMODITY DERIVATIVE FINANCIAL INSTRUMENTS The Partnership’s ongoing operations expose it to changes in the market price for oil and natural gas. To mitigate the inherent commodity price risk associated with its operations, the Partnership uses oil and natural gas commodity derivative financial instruments. From time to time, such instruments may include variable-to-fixed-price swaps, costless collars, fixed-price contracts and other contractual arrangements. The Partnership enters into oil and natural gas derivative contracts that contain netting arrangements with each counterparty. The Partnership does not enter into derivative instruments for speculative purposes. As of September 30, 2019, the Partnership’s open derivative contracts consisted of fixed-price swap contracts and costless collar contracts. A fixed-price swap contract between the Partnership and the counterparty specifies a fixed commodity price and a future settlement date. A costless collar contract between the Partnership and the counterparty specifies a floor and a ceiling commodity price and a future settlement date. The Partnership has not designated any of its contracts as fair value or cash flow hedges. Accordingly, the changes in the fair value of the contracts are included in the consolidated statement of operations in the period of the change. All derivative gains and losses from the Partnership’s derivative contracts have been recognized in revenue in the Partnership's accompanying consolidated statements of operations. Derivative instruments that have not yet been settled in cash are reflected as either derivative assets or liabilities in the Partnership’s accompanying consolidated balance sheets as of September 30, 2019 and December 31, 2018. See Note 6 – Fair Value Measurements for further discussion. The Partnership's derivative contracts expose it to credit risk in the event of nonperformance by counterparties that may adversely impact the fair value of the Partnership's commodity derivative assets. While the Partnership does not require its derivative contract counterparties to post collateral, the Partnership does evaluate the credit standing of such counterparties as deemed appropriate. This evaluation includes reviewing a counterparty’s credit rating and latest financial information. As of September 30, 2019, the Partnership had nine counterparties, all of which are rated Baa1 or better by Moody’s and are lenders under the Credit Facility. The tables below summarize the fair values and classifications of the Partnership’s derivative instruments, as well as the gross recognized derivative assets, liabilities, and amounts offset in the consolidated balance sheets as of each date: September 30, 2019 Classification Balance Sheet Location Gross Effect of Counterparty Netting Net Carrying Value on Balance Sheet (in thousands) Assets: Current asset Commodity derivative assets $ 33,710 $ (656) $ 33,054 Long-term asset Deferred charges and other long-term assets 9,269 (311) 8,958 Total assets $ 42,979 $ (967) $ 42,012 Liabilities: Current liability Commodity derivative liabilities $ 656 $ (656) $ — Long-term liability Commodity derivative liabilities 311 (311) — Total liabilities $ 967 $ (967) $ — December 31, 2018 Classification Balance Sheet Location Gross Effect of Counterparty Netting Net Carrying Value on Balance Sheet (in thousands) Assets: Current asset Commodity derivative assets $ 38,746 $ (776) $ 37,970 Long-term asset Deferred charges and other long-term assets 11,518 (1,450) 10,068 Total assets $ 50,264 $ (2,226) $ 48,038 Liabilities: Current liability Commodity derivative liabilities $ 776 $ (776) $ — Long-term liability Commodity derivative liabilities 1,450 (1,450) — Total liabilities $ 2,226 $ (2,226) $ — Changes in the fair values of the Partnership’s derivative instruments (both assets and liabilities) are presented on a net basis in the accompanying consolidated statements of operations and consolidated statements of cash flows and consist of the following for the periods presented: Three Months Ended Nine Months Ended Derivatives not designated as hedging instruments 2019 2018 2019 2018 (in thousands) Beginning fair value of commodity derivative instruments $ 31,368 $ (44,043) $ 48,038 $ (5,028) Gain (loss) on oil derivative instruments 18,132 (18,830) (13,224) (63,325) Gain (loss) on natural gas derivative instruments 6,158 316 25,518 (4,869) Net cash paid (received) on settlements of oil derivative instruments (2,938) 11,280 (5,748) 25,809 Net cash paid (received) on settlements of natural gas derivative instruments (10,708) (1,484) (12,572) (5,348) Net change in fair value of commodity derivative instruments 10,644 (8,718) (6,026) (47,733) Ending fair value of commodity derivative instruments $ 42,012 $ (52,761) $ 42,012 $ (52,761) The Partnership had the following open derivative contracts for oil as of September 30, 2019: Weighted Average Price (Per Bbl) Range (Per Bbl) Period and Type of Contract Volume (Bbl) Low High Oil Swap Contracts: 2019 Third Quarter 285,000 $ 58.37 $ 52.82 $ 63.75 Fourth Quarter 936,000 58.50 52.82 63.75 2020 First Quarter 510,000 $ 57.14 $ 54.92 $ 58.65 Second Quarter 510,000 57.14 54.92 58.65 Third Quarter 510,000 57.14 54.92 58.65 Fourth Quarter 510,000 57.14 54.92 58.65 Weighted Average Weighted Average Period and Type of Contract Volume (Bbl) Oil Collar Contracts: 2019 Third Quarter 20,000 $ 65.00 $ 74.00 Fourth Quarter 60,000 65.00 74.00 2020 First Quarter 210,000 $ 56.43 $ 67.14 Second Quarter 210,000 56.43 67.14 Third Quarter 210,000 56.43 67.14 Fourth Quarter 210,000 56.43 67.14 The Partnership had the following open derivative contracts for natural gas as of September 30, 2019: Weighted Average Price (Per MMBtu) Range (Per MMBtu) Period and Type of Contract Volume (MMBtu) Low High Natural Gas Swap Contracts: 2019 Fourth Quarter 14,640,000 $ 2.96 $ 2.81 $ 3.20 2020 First Quarter 10,010,000 $ 2.69 $ 2.55 $ 2.74 Second Quarter 10,010,000 2.69 2.55 2.74 Third Quarter 10,120,000 2.69 2.55 2.74 Fourth Quarter 10,120,000 2.69 2.55 2.74

Fair Value Measurements

Fair Value Measurements	9 Months Ended
	Sep. 30, 2019
Fair Value Disclosures [Abstract]
Fair Value Measurements	FAIR VALUE MEASUREMENTS Fair value is defined as the amount at which an asset (or liability) could be bought (or incurred) or sold (or settled) in an orderly transaction between market participants at the measurement date. Further, ASC 820, Fair Value Measurement , establishes a framework for measuring fair value, establishes a fair value hierarchy based on the quality of inputs used to measure fair value, and includes certain disclosure requirements. Fair value estimates are based on either (i) actual market data or (ii) assumptions that other market participants would use in pricing an asset or liability, including estimates of risk. ASC 820 establishes a three-level valuation hierarchy for disclosure of fair value measurements. The valuation hierarchy categorizes assets and liabilities measured at fair value into one of three different levels depending on the observability of the inputs employed in the measurement. The three levels are defined as follows: Level 1 —Unadjusted quoted prices for identical assets or liabilities in active markets. Level 2 —Quoted prices for similar assets or liabilities in non-active markets, and inputs that are observable for the asset or liability, either directly or indirectly, for substantially the full term of the financial instrument. Level 3 —Inputs that are unobservable and significant to the fair value measurement (including the Partnership’s own assumptions in determining fair value). A financial instrument’s categorization within the valuation hierarchy is based upon the lowest level of input that is significant to the fair value measurement. The Partnership’s assessment of the significance of a particular input to the fair value measurement in its entirety requires judgment and considers factors specific to the asset or liability. There were no transfers into, or out of, the three levels of the fair value hierarchy for the nine months ended September 30, 2019 or the year ended December 31, 2018. The carrying value of the Partnership's cash and cash equivalents, receivables, and payables approximate fair value due to the short-term nature of the instruments. The estimated carrying value of all debt as of September 30, 2019 and December 31, 2018 approximated the fair value due to variable market rates of interest. These debt fair values, which are Level 3 measurements, were estimated based on the Partnership’s incremental borrowing rates for similar types of borrowing arrangements, when quoted market prices were not available. The estimated fair values of the Partnership’s financial instruments are not necessarily indicative of the amounts that would be realized in a current market exchange. Assets and Liabilities Measured at Fair Value on a Recurring Basis The Partnership estimated the fair value of derivative instruments using the market approach via a model that uses inputs that are observable in the market or can be derived from, or corroborated by, observable data. See Note 5 – Commodity Derivative Financial Instruments for further discussion. The following table presents information about the Partnership’s assets and liabilities measured at fair value on a recurring basis: Fair Value Measurements Using Effect of Counterparty Netting Total Level 1 Level 2 Level 3 (in thousands) As of September 30, 2019 Financial Assets Commodity derivative instruments $ — $ 42,979 $ — $ (967) $ 42,012 Financial Liabilities Commodity derivative instruments $ — $ 967 $ — $ (967) $ — As of December 31, 2018 Financial Assets Commodity derivative instruments $ — $ 50,264 $ — $ (2,226) $ 48,038 Financial Liabilities Commodity derivative instruments $ — $ 2,226 $ — $ (2,226) $ — Assets and Liabilities Measured at Fair Value on a Non-Recurring Basis Nonfinancial assets and liabilities measured at fair value on a non-recurring basis include certain nonfinancial assets and liabilities as may be acquired in a business combination and measurements of oil and natural gas property values for assessment of impairment. The determination of the fair values of proved and unproved properties acquired in business combinations are estimated by discounting projected future cash flows. The factors used to determine fair value include estimates of economic reserves, future operating and development costs, future commodity prices, timing of future production, and a risk-adjusted discount rate. The Partnership has designated these measurements as Level 3. The Partnership’s fair value assessments for recent acquisitions are included in Note 4 – Oil and Natural Gas Properties. Oil and natural gas properties are measured at fair value on a non-recurring basis using the income approach when assessing for impairment. Proved and unproved oil and natural gas properties are reviewed for impairment when events and circumstances indicate a possible decline in the recoverability of the carrying value of those properties. When assessing producing properties for impairment, the Partnership compares the expected undiscounted projected future cash flows of the producing properties to the carrying amount of the producing properties to determine recoverability. When the carrying amount exceeds its estimated undiscounted future cash flows, the carrying amount is written down to its fair value, which is measured as the present value of the projected future cash flows of such properties. The factors used to determine fair value include estimates of proved reserves, future commodity prices, timing of future production, operating costs, future capital expenditures, and a risk-adjusted discount rate. The Partnership’s estimates of fair value have been determined at discrete points in time based on relevant market data. These estimates involve uncertainty and cannot be determined with precision. There were no significant changes in valuation techniques or related inputs as of September 30, 2019 or December 31, 2018. There were no assets measured at fair value on a non-recurring basis, after initial recognition, for the nine months ended September 30, 2019 and 2018.

Credit Facility

Credit Facility	9 Months Ended
	Sep. 30, 2019
Debt Disclosure [Abstract]
Credit Facility	CREDIT FACILITY The Partnership maintains a senior secured revolving credit agreement, as amended (the “Credit Facility”). The Credit Facility has an aggregate maximum credit amount of $1.0 billion and terminates on November 1, 2022. The commitment of the lenders equals the lesser of the aggregate maximum credit amount and the borrowing base. The amount of the borrowing base is redetermined semi-annually, usually in October and April, and is derived from the value of the Partnership’s oil and natural gas properties as determined by the lender syndicate using pricing assumptions that often differ from the current market for future prices. Effective May 4, 2018, the borrowing base redetermination increased the borrowing base from $550.0 million to $600.0 million. Effective October 31, 2018, the borrowing base was further increased to $675.0 million and remained at that level until the most recent redetermination, effective October 23, 2019, which reduced the borrowing base to $650.0 million. Outstanding borrowings under the Credit Facility bear interest at a floating rate elected by the Partnership equal to an alternative base rate (which is equal to the greatest of the Prime Rate, the Federal Funds effective rate plus 0.50%, or 1-month LIBOR plus 1.00%) or LIBOR, in each case, plus the applicable margin. Prior to October 31, 2018, the applicable margin ranged from 1.00% to 2.00% in the case of the alternative base rate and from 2.00% to 3.00% in the case of LIBOR, depending on the borrowings outstanding in relation to the borrowing base. Effective October 31, 2018, the applicable margin for the alternative base rate was reduced to between 0.75% and 1.75% and the applicable margin for LIBOR was reduced to between 1.75% and 2.75%. The weighted-average interest rate of the Credit Facility was 4.30% and 4.76% as of September 30, 2019 and December 31, 2018, respectively. Accrued interest is payable at the end of each calendar quarter or at the end of each interest period, unless the interest period is longer than 90 days, in which case interest is payable at the end of every 90-day period. In addition, a commitment fee is payable at the end of each calendar quarter based on either a rate of 0.375% if the borrowing base utilization percentage is less than 50%, or 0.500% if the borrowing base utilization percentage is equal to or greater than 50%. The Credit Facility is secured by substantially all of the Partnership’s oil and natural gas production and assets. The Credit Facility contains various limitations on future borrowings, leases, hedging, and sales of assets. Additionally, the Credit Facility requires the Partnership to maintain a current ratio of not less than 1.0:1.0 and a ratio of total debt to EBITDAX (Earnings before Interest, Taxes, Depreciation, Amortization, and Exploration) of not more than 3.5:1.0. As of September 30, 2019, the Partnership was in compliance with all financial covenants in the Credit Facility. The aggregate principal balance outstanding was $413.0 million and $410.0 million at September 30, 2019 and December 31, 2018, respectively. The unused portion of the available borrowings under the Credit Facility were $262.0 million and $265.0 million at September 30, 2019 and December 31, 2018, respectively.

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2019
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	COMMITMENTS AND CONTINGENCIES Environmental Matters The Partnership’s business includes activities that are subject to U.S. federal, state, and local environmental regulations with regard to air, land, and water quality and other environmental matters. The Partnership does not consider the potential remediation costs that could result from issues identified in any environmental site assessments to be significant to the consolidated financial statements, and no provision for potential remediation costs has been recorded. Put Option Related to Noble Acquisition By acquiring 100% of the issued and outstanding securities of Samedan Royalty, LLC, now NAMP Holdings, LLC, on November 28, 2017 from Noble Energy US Holdings, LLC, the Partnership acquired a 100% interest in Comin-Temin, LLC, now NAMP GP, LLC ("Holdings"), Comin 1989 Partnership LLLP, now NAMP 1, LP ("Comin"), and Temin 1987 Partnership LLLP, now NAMP 2, LP ("Temin"). Pursuant to certain co-ownership agreements, various co-owners hold undivided beneficial ownership interests in 45.33% and 42.63% of the minerals interests held of record by Holdings and Temin, respectively as of September 30, 2019. Based on the terms of the co-ownership agreements, the co-owners each have an unconditional option to require Comin or Temin, as applicable, to purchase their beneficial ownership interest in the mineral interests held of record by Holdings or Temin, as applicable, at any time within 30 days of receiving such repurchase notice. The purchase price of the beneficial ownership interest shall be based on an evaluation performed by Comin or Temin, as applicable, in good faith. As of September 30, 2019, the Partnership had not received notice from any co-owners to exercise their repurchase option, and as such, no liability was recorded. Litigation

Incentive Compensation

Incentive Compensation	9 Months Ended
	Sep. 30, 2019
Share-based Payment Arrangement [Abstract]
Incentive Compensation	INCENTIVE COMPENSATION The table below summarizes incentive compensation expense recorded in the General and administrative line item of the consolidated statements of operations for the periods presented: Three Months Ended September 30, Nine Months Ended 2019 2018 2019 2018 (in thousands) Cash—short and long-term incentive plans $ 1,092 $ 4,366 $ 4,336 $ 7,568 Equity-based compensation—restricted common and subordinated units 2,552 3,404 8,162 10,180 Equity-based compensation—restricted performance units 727 5,611 6,984 13,026 Board of Directors incentive plan 587 581 1,760 1,741 Total incentive compensation expense $ 4,958 $ 13,962 $ 21,242 $ 32,515

Preferred Units

Preferred Units	9 Months Ended
	Sep. 30, 2018
Equity [Abstract]
Preferred Units	PREFERRED UNITS Series A Redeemable Preferred Units As of September 30, 2019 and December 31, 2018, there were no Series A redeemable preferred units outstanding. The Series A redeemable preferred units were entitled to an annual distribution of 10% of the outstanding funded capital of the Series A redeemable preferred units, payable on a quarterly basis in arrears. The Series A redeemable preferred units were convertible into common and subordinated units at any time at the option of the Series A redeemable preferred unitholders. The Series A redeemable preferred units had an adjusted conversion price of $14.2683 and an adjusted conversion rate of 30.3431 common units and 39.7427 subordinated units per redeemable preferred unit. The Series A redeemable preferred unitholders had the option to elect to have the Partnership redeem, at face value, all remaining Series A redeemable preferred units, effective as of December 31, 2017, plus any accrued and unpaid distributions. All Series A redeemable preferred units not redeemed by March 31, 2018 automatically converted to common and subordinated units effective as of January 1, 2018 or as soon as practicable thereafter. For the nine months ended September 30, 2018, 2,115 Series A redeemable preferred units were redeemed for $2.1 million, including accrued unpaid yield, and 24,248 Series A redeemable preferred units totaling $24.2 million were converted into 735,758 common units and 963,681 subordinated units as a result of the mandatory conversion subsequent to December 31, 2017. Series B Cumulative Convertible Preferred Units On November 28, 2017, the Partnership issued and sold in a private placement 14,711,219 Series B cumulative convertible preferred units representing limited partner interests in the Partnership for a cash purchase price of $20.3926 per Series B cumulative convertible preferred unit, resulting in total proceeds of approximately $300.0 million. The Series B cumulative convertible preferred units are entitled to an annual distribution of 7%, payable on a quarterly basis in arrears. For the eight quarters consisting of the quarter in respect of which the initial distribution is paid and the seven full quarters thereafter, the quarterly distribution may be paid, at the sole option of the Partnership, (i) in-kind in the form of additional Series B cumulative convertible preferred units (the "Series B PIK Units"), (ii) in cash, or (iii) in a combination of Series B PIK Units and cash. Beginning with the ninth quarter, all Series B cumulative convertible preferred unit distributions shall be paid in cash. The number of Series B PIK Units to be issued, if any, shall equal the quotient of the Series B cumulative convertible preferred unit distribution amount (or portion thereof) divided by the Series B cumulative convertible preferred unit purchase price of $20.3926. The Series B cumulative convertible preferred units are convertible into common units of the Partnership on November 29, 2019 and once per quarter thereafter. At such time, the Series B cumulative convertible preferred units may be converted by each holder at its option, in whole or in part, into common units on a one-for-one basis at the purchase price of $20.3926, adjusted to give effect to any accrued but unpaid accumulated distributions on the applicable Series B cumulative convertible preferred units through the most recent declaration date. However, the Partnership shall not be obligated to honor any request for such conversion if such request does not involve an underlying value of common units of at least $10.0 million based on the closing trading price of common units on the trading day immediately preceding the conversion notice date, or such lesser amount to the extent such exercise covers all of a holder's Series B cumulative convertible preferred units. The Series B cumulative convertible preferred units had a carrying value of $298.4 million, including accrued distributions of $5.3 million, as of September 30, 2019 and December 31, 2018. The Series B cumulative convertible preferred units are classified as mezzanine equity on the consolidated balance sheets since certain provisions of redemption are outside the control of the Partnership.

Common and Subordinated Units

Common and Subordinated Units	9 Months Ended
	Sep. 30, 2019
Share-based Payment Arrangement [Abstract]
Common and Subordinated Units	COMMON AND SUBORDINATED UNITS Common and Subordinated Units The common units and subordinated units represent limited partner interests in the Partnership. The partnership agreement restricts unitholders’ voting rights by providing that any units held by a person or group that owns 15% or more of any class of units then outstanding, other than the limited partners in Black Stone Minerals Company, L.P. prior to the initial public offering of BSM, their transferees, persons who acquired such units with the prior approval of the board of directors of the Partnership's general partner (the "Board"), holders of Series B cumulative convertible preferred units in connection with any vote, consent or approval of the Series B cumulative convertible preferred units as a separate class, and persons who own 15% or more of any class as a result of any redemption or purchase of any other person's units or similar action by the Partnership or any conversion of the Series B cumulative convertible preferred units at the Partnership's option or in connection with a change of control, may not vote on any matter. Prior to the end of the subordination period (as defined in the partnership agreement), the holders of common units and subordinated units were entitled to participate in distributions and exercise the rights and privileges provided to limited partners holding common units and subordinated units under the partnership agreement. The partnership agreement generally provides that any distributions during the subordination period are paid each quarter in the following manner: • first , to the holders of the Series B cumulative convertible preferred units in an amount equal to 7% per annum, subject to certain adjustments; • second , to the holders of common units, until each common unit has received the applicable minimum quarterly distribution plus any arrearages from prior quarters; and • third , to the holders of subordinated units, until each subordinated unit has received the applicable minimum quarterly distribution. If the distributions to common and subordinated unitholders exceeded the applicable minimum quarterly distribution per unit, then such excess amounts were distributed pro rata on the common and subordinated units as if they were a single class. In connection with the expiration of the subordination period, each outstanding subordinated unit converted into one common unit on May 24, 2019 and the priority right of the common unitholders ceased to exist. The following table provides information about the Partnership's per unit distributions to common unitholders: Three Months Ended September 30, Nine Months Ended September 30, 2019 2018 2019 2018 DISTRIBUTIONS DECLARED AND PAID: Per common unit $ 0.3700 $ 0.3375 $ 1.1100 $ 0.9625 The Partnership's per unit distributions declared and paid to subordinated unitholders for the three and nine months ended September 30, 2018 were $0.3375 and $0.7550, respectively. For the three months ended September 30, 2019 there were no subordinated distributions as all subordinated units converted into common units on May 24, 2019. The Partnership's per unit distributions declared and paid to subordinated unitholders for the six months ended June 30, 2019 were $0.7400. End of the Subordination Period The subordination period under the partnership agreement ended on the first business day after the Partnership earned and paid an aggregate amount of at least $1.35 (the annualized minimum quarterly distribution applicable for quarterly periods ending March 31, 2019 and thereafter) multiplied by the total number of outstanding common and subordinated units for a period of four consecutive, non-overlapping quarters ending on or after March 31, 2019, and there were no outstanding arrearages on the common units. This test was met upon the payment of the distribution for the first quarter of 2019. Accordingly, 96,328,836 subordinated units converted into 96,328,836 common units on May 24, 2019 and common units are no longer entitled to arrearages. Common Unit Repurchase Program On November 5, 2018, the Board authorized the repurchase of up to $75.0 million in common units. The repurchase program authorizes the Partnership to make repurchases on a discretionary basis as determined by management, subject to market conditions, applicable legal requirements, available liquidity, and other appropriate factors. The Partnership repurchased a total of 136,665 common units for an aggregate cost of $2.2 million under this program for the nine months ended September 30, 2019. As of September 30, 2019, the Partnership has repurchased $4.2 million in common units under the repurchase program since inception. The repurchase program is funded from the Partnership's cash on hand or availability on the Credit Facility. Any repurchased units are canceled. At-The-Market Offering Program On May 26, 2017, the Partnership commenced an at-the-market offering program (the “ATM Program”) and in connection therewith entered into an Equity Distribution Agreement with Wells Fargo Securities, LLC, Merrill Lynch, Pierce, Fenner & Smith Incorporated, and UBS Securities LLC, as Sales Agents (each a “Sales Agent” and collectively the “Sales Agents”). Pursuant to the terms of the ATM Program, the Partnership may sell, from time to time through the Sales Agents, the Partnership’s common units representing limited partner interests having an aggregate offering amount of up to $100,000,000. Sales of common units, may be made in negotiated transactions or transactions that are deemed to be “at the market” offerings as defined in Rule 415 under the Securities Act of 1933, as amended (the “Securities Act”), including sales made directly on the New York Stock Exchange or sales made to or through a market maker other than on an exchange. Under the terms of the ATM Program, the Partnership may also sell common units to one or more of the Sales Agents as principal for its own account at a price to be agreed upon at the time of sale. Any sale of common units to a Sales Agent as principal would be pursuant to the terms of a separate agreement between the Partnership and such Sales Agent. The Partnership intends to use the net proceeds from any sales pursuant to the ATM Program, after deducting the Sales Agents’ commissions and the Partnership’s offering expenses, for general partnership purposes, which may include, among other things, repayment of indebtedness outstanding under the Partnership’s Credit Facility. Common units sold pursuant to the Equity Distribution Agreement are offered and sold pursuant to the Partnership’s existing effective shelf-registration statement on Form S-3 (File No. 333-215857), which was declared effective by the SEC on February 8, 2017. The Equity Distribution Agreement contains customary representations, warranties and agreements, indemnification obligations, including for liabilities under the Securities Act, other obligations of the parties and termination provisions. For the nine months ended September 30, 2019, the Partnership sold no common units under the ATM Program. For the nine months ended September 30, 2018, the Partnership sold 2,121,643 common units under the ATM program for net proceeds of $38.4 million. As of September 30, 2019, the Partnership has raised net proceeds of $73.0 million under the ATM Program since inception.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2019
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying unaudited interim consolidated financial statements of the Partnership have been prepared in accordance with generally accepted accounting principles ("GAAP") in the United States and pursuant to the rules and regulations of the U.S. Securities and Exchange Commission (“SEC”). These unaudited interim consolidated financial statements have been prepared in accordance with the instructions to Form 10-Q and, therefore, do not include all disclosures required for financial statements prepared in conformity with GAAP. Accordingly, the accompanying unaudited interim consolidated financial statements and related notes should be read in conjunction with the Partnership’s consolidated financial statements included in the Partnership’s Annual Report on Form 10-K for the year ended December 31, 2018 ("2018 Annual Report on Form 10-K"). The unaudited interim consolidated financial statements include the consolidated results of the Partnership. The results of operations for the nine months ended September 30, 2019 are not necessarily indicative of the results to be expected for the full year. In the opinion of management, all adjustments, which are of a normal and recurring nature, necessary for the fair presentation of the financial results for all periods presented have been reflected. All intercompany balances and transactions have been eliminated. The Partnership evaluates the significant terms of its investments to determine the method of accounting to be applied to each respective investment. Investments in which the Partnership has less than a 20% ownership interest and does not have control or exercise significant influence are accounted for using fair value or cost minus impairment if fair value is not readily determinable. Investments in which the Partnership exercises control are consolidated, and the noncontrolling interests of such investments, which are not attributable directly or indirectly to the Partnership, are presented as a separate component of net income (loss) and equity in the accompanying unaudited interim consolidated financial statements. The unaudited interim consolidated financial statements include undivided interests in oil and natural gas property rights. The Partnership accounts for its share of oil and natural gas property rights by reporting its proportionate share of assets, liabilities, revenues, costs, and cash flows within the relevant lines on the accompanying unaudited interim consolidated balance sheets, statements of operations, and statements of cash flows.
Segment Reporting	Segment Reporting The Partnership operates in a single operating and reportable segment. Operating segments are defined as components of an enterprise for which separate financial information is evaluated regularly by the chief operating decision maker in deciding how to allocate resources and assess performance. The Partnership’s chief executive officer has been determined to be the chief operating decision maker and allocates resources and assesses performance based upon financial information at the consolidated level.
New Accounting Pronouncements	Recent Accounting Pronouncements In February 2016, the Financial Accounting Standards Board ("FASB") issued Accounting Standards Update ("ASU") 2016-02, Leases (Topic 842) ("ASC 842"), that supersedes Accounting Standards Codification ("ASC") 840, Leases by requiring lessees to recognize lease assets and lease liabilities classified as operating leases on the balance sheet. See Note 3 - Impact of ASC 842 Adoption for further details related to the Partnership's adoption of this standard. In August 2018, the FASB issued ASU 2018-13, Fair Value Measurement (Topic 820)
Earnings Per Unit	The Partnership applies the two-class method for purposes of calculating earnings per unit (“EPU”). The holders of the Partnership’s restricted common units have all the rights of a unitholder, including non-forfeitable distribution rights. As participating securities, the restricted common units are included in the calculation of basic earnings per unit. For the periods presented, the amount of earnings allocated to these participating units was not material. Net income (loss) attributable to the Partnership is allocated to the Partnership’s general partner and the common and subordinated unitholders in proportion to their pro rata ownership after giving effect to distributions, if any, declared during the period.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies - (Tables)	9 Months Ended
	Sep. 30, 2019
Accounting Policies [Abstract]
Schedule of Accounts Receivable	The following table presents information about the Partnership's accounts receivable: September 30, 2019 December 31, 2018 (in thousands) Accounts receivable: Revenues from contracts with customers $ 77,837 $ 107,804 Other 7,005 5,344 Total accounts receivable $ 84,842 $ 113,148

Oil and Natural Gas Properties

Oil and Natural Gas Properties (Tables)	9 Months Ended
	Sep. 30, 2019
Business Acquisition [Line Items]
Schedule of Fair Values of the Properties Acquired	The following table summarizes these acquisitions which were considered business combinations: Assets Acquired Consideration Paid Proved Unproved Net Working Capital Total Fair Value Cash (in thousands) February $ 173 $ 8,437 $ 1 $ 8,611 $ 8,611 March 24 — — 24 24 June 527 3,268 — 3,795 3,795 Total fair value $ 724 $ 11,705 $ 1 $ 12,430 $ 12,430
Permian Basin
Business Acquisition [Line Items]
Schedule of Fair Values of the Properties Acquired	The following table summarizes these acquisitions which were considered business combinations: Assets Acquired Consideration Paid Proved Unproved Net Working Capital Total Fair Value Cash Fair Value of Common Units Issued (in thousands) March $ 984 $ 21,452 $ 133 $ 22,569 $ 22,569 $ — June 883 13,688 8 14,579 14,579 — July 4,349 7,944 215 12,508 3,764 8,744 August 5,000 34,673 74 39,747 26,461 13,286 September 1,176 — — 1,176 1,176 — November 1,166 — — 1,166 1,166 — Total fair value $ 13,558 $ 77,757 $ 430 $ 91,745 $ 69,715 $ 22,030

Commodity Derivative Financia_2

Commodity Derivative Financial Instruments (Tables)	9 Months Ended
	Sep. 30, 2019
Derivative [Line Items]
Summary of Fair Value and Classification of Derivative Instruments	The tables below summarize the fair values and classifications of the Partnership’s derivative instruments, as well as the gross recognized derivative assets, liabilities, and amounts offset in the consolidated balance sheets as of each date: September 30, 2019 Classification Balance Sheet Location Gross Effect of Counterparty Netting Net Carrying Value on Balance Sheet (in thousands) Assets: Current asset Commodity derivative assets $ 33,710 $ (656) $ 33,054 Long-term asset Deferred charges and other long-term assets 9,269 (311) 8,958 Total assets $ 42,979 $ (967) $ 42,012 Liabilities: Current liability Commodity derivative liabilities $ 656 $ (656) $ — Long-term liability Commodity derivative liabilities 311 (311) — Total liabilities $ 967 $ (967) $ — December 31, 2018 Classification Balance Sheet Location Gross Effect of Counterparty Netting Net Carrying Value on Balance Sheet (in thousands) Assets: Current asset Commodity derivative assets $ 38,746 $ (776) $ 37,970 Long-term asset Deferred charges and other long-term assets 11,518 (1,450) 10,068 Total assets $ 50,264 $ (2,226) $ 48,038 Liabilities: Current liability Commodity derivative liabilities $ 776 $ (776) $ — Long-term liability Commodity derivative liabilities 1,450 (1,450) — Total liabilities $ 2,226 $ (2,226) $ —
Changes in Fair Value of Company's Commodity Derivative Instruments	Changes in the fair values of the Partnership’s derivative instruments (both assets and liabilities) are presented on a net basis in the accompanying consolidated statements of operations and consolidated statements of cash flows and consist of the following for the periods presented: Three Months Ended Nine Months Ended Derivatives not designated as hedging instruments 2019 2018 2019 2018 (in thousands) Beginning fair value of commodity derivative instruments $ 31,368 $ (44,043) $ 48,038 $ (5,028) Gain (loss) on oil derivative instruments 18,132 (18,830) (13,224) (63,325) Gain (loss) on natural gas derivative instruments 6,158 316 25,518 (4,869) Net cash paid (received) on settlements of oil derivative instruments (2,938) 11,280 (5,748) 25,809 Net cash paid (received) on settlements of natural gas derivative instruments (10,708) (1,484) (12,572) (5,348) Net change in fair value of commodity derivative instruments 10,644 (8,718) (6,026) (47,733) Ending fair value of commodity derivative instruments $ 42,012 $ (52,761) $ 42,012 $ (52,761)
Oil and Natural Gas
Derivative [Line Items]
Summary of Open Derivative Contracts	The Partnership had the following open derivative contracts for oil as of September 30, 2019: Weighted Average Price (Per Bbl) Range (Per Bbl) Period and Type of Contract Volume (Bbl) Low High Oil Swap Contracts: 2019 Third Quarter 285,000 $ 58.37 $ 52.82 $ 63.75 Fourth Quarter 936,000 58.50 52.82 63.75 2020 First Quarter 510,000 $ 57.14 $ 54.92 $ 58.65 Second Quarter 510,000 57.14 54.92 58.65 Third Quarter 510,000 57.14 54.92 58.65 Fourth Quarter 510,000 57.14 54.92 58.65 Weighted Average Weighted Average Period and Type of Contract Volume (Bbl) Oil Collar Contracts: 2019 Third Quarter 20,000 $ 65.00 $ 74.00 Fourth Quarter 60,000 65.00 74.00 2020 First Quarter 210,000 $ 56.43 $ 67.14 Second Quarter 210,000 56.43 67.14 Third Quarter 210,000 56.43 67.14 Fourth Quarter 210,000 56.43 67.14 The Partnership had the following open derivative contracts for natural gas as of September 30, 2019: Weighted Average Price (Per MMBtu) Range (Per MMBtu) Period and Type of Contract Volume (MMBtu) Low High Natural Gas Swap Contracts: 2019 Fourth Quarter 14,640,000 $ 2.96 $ 2.81 $ 3.20 2020 First Quarter 10,010,000 $ 2.69 $ 2.55 $ 2.74 Second Quarter 10,010,000 2.69 2.55 2.74 Third Quarter 10,120,000 2.69 2.55 2.74 Fourth Quarter 10,120,000 2.69 2.55 2.74

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 2019
Fair Value Disclosures [Abstract]
Schedule of Assets and Liabilities Measured at Fair Value on a Recurring Basis	The following table presents information about the Partnership’s assets and liabilities measured at fair value on a recurring basis: Fair Value Measurements Using Effect of Counterparty Netting Total Level 1 Level 2 Level 3 (in thousands) As of September 30, 2019 Financial Assets Commodity derivative instruments $ — $ 42,979 $ — $ (967) $ 42,012 Financial Liabilities Commodity derivative instruments $ — $ 967 $ — $ (967) $ — As of December 31, 2018 Financial Assets Commodity derivative instruments $ — $ 50,264 $ — $ (2,226) $ 48,038 Financial Liabilities Commodity derivative instruments $ — $ 2,226 $ — $ (2,226) $ —

Incentive Compensation (Tables)

Incentive Compensation (Tables)	9 Months Ended
	Sep. 30, 2019
Share-based Payment Arrangement [Abstract]
Summary of Incentive Compensation Expense	The table below summarizes incentive compensation expense recorded in the General and administrative line item of the consolidated statements of operations for the periods presented: Three Months Ended September 30, Nine Months Ended 2019 2018 2019 2018 (in thousands) Cash—short and long-term incentive plans $ 1,092 $ 4,366 $ 4,336 $ 7,568 Equity-based compensation—restricted common and subordinated units 2,552 3,404 8,162 10,180 Equity-based compensation—restricted performance units 727 5,611 6,984 13,026 Board of Directors incentive plan 587 581 1,760 1,741 Total incentive compensation expense $ 4,958 $ 13,962 $ 21,242 $ 32,515

Earnings Per Unit (Tables)

Earnings Per Unit (Tables)	9 Months Ended
	Sep. 30, 2019
Earnings Per Share [Abstract]
Computation of Basic and Diluted Earnings per Common and Subordinated Unit	The following table sets forth the computation of basic and diluted earnings per common and subordinated unit: Three Months Ended Nine Months Ended 2019 2018 2019 2018 (in thousands, except per unit amounts) NET INCOME (LOSS) $ 70,247 $ 60,775 $ 174,351 $ 131,422 Net (income) loss attributable to noncontrolling interests — (22) — (1) Distributions on Series A redeemable preferred units — — — (25) Distributions on Series B cumulative convertible preferred units (5,250) (5,250) (15,750) (15,750) NET INCOME (LOSS) ATTRIBUTABLE TO THE GENERAL PARTNER AND COMMON AND SUBORDINATED UNITS 64,997 55,503 158,601 115,646 ALLOCATION OF NET INCOME (LOSS): General partner interest $ — $ — $ — $ — Common units 64,997 29,188 134,608 71,037 Subordinated units — 26,315 23,993 44,609 $ 64,997 $ 55,503 $ 158,601 $ 115,646 Weighted average common units outstanding: Weighted average common units outstanding (basic) 205,957 106,706 155,513 105,254 Effect of dilutive securities — — — — Weighted average common units outstanding (diluted) 205,957 106,706 155,513 105,254 Weighted average subordinated units outstanding: Weighted average subordinated units outstanding (basic) — 96,329 50,458 96,021 Effect of dilutive securities — — — — Weighted average subordinated units outstanding (diluted) — 96,329 50,458 96,021 NET INCOME (LOSS) ATTRIBUTABLE TO LIMITED PARTNERS PER COMMON AND SUBORDINATED UNIT: Per common unit (basic) $ 0.32 $ 0.27 $ 0.87 $ 0.67 Per subordinated unit (basic) — 0.27 0.48 0.46 Per common unit (diluted) 0.32 0.27 0.87 0.67 Per subordinated unit (diluted) — 0.27 0.48 0.46
Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share	The following units of potentially dilutive securities were excluded from the computation of diluted weighted average units outstanding because their inclusion would be anti-dilutive: Three Months Ended Nine Months Ended 2019 2018 2019 2018 (in thousands) Potentially dilutive securities (common units): Series A redeemable preferred units on an as-converted basis — — — 189 Series B cumulative convertible preferred units on an as-converted basis 14,969 14,969 14,969 14,969 14,969 14,969 14,969 15,158 Potentially dilutive securities (subordinated units): Series A redeemable preferred units on an as-converted basis — — — 247

Common and Subordinated Units (

Common and Subordinated Units (Tables)	9 Months Ended
	Sep. 30, 2019
Share-based Payment Arrangement [Abstract]
Distributions Made to Limited Partner, by Distribution	The following table provides information about the Partnership's per unit distributions to common unitholders: Three Months Ended September 30, Nine Months Ended September 30, 2019 2018 2019 2018 DISTRIBUTIONS DECLARED AND PAID: Per common unit $ 0.3700 $ 0.3375 $ 1.1100 $ 0.9625

Business and Basis of Present_2

Business and Basis of Presentation - Additional Information (Details)	Sep. 30, 2019state
Limited Partners Capital Account [Line Items]
Cost basis, ownership percentage	20.00%
U.S.
Limited Partners Capital Account [Line Items]
Number of states major onshore oil and natural gas basins located	41

Summary of Significant Accoun_4

Summary of Significant Accounting Policies Accounts Receivable (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable	$ 84,842	$ 113,148
Revenues from contracts with customers
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable	77,837	107,804
Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable	$ 7,005	$ 5,344

Impact of ASC 842 Adoption - Na

Impact of ASC 842 Adoption - Narrative (Details)	9 Months Ended
	Sep. 30, 2019
Assets, Total | Lease Concentration Risk
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Concentration risk, percentage	1.00%

Oil and Natural Gas Propertie_2

Oil and Natural Gas Properties - Schedule of Fair Values of the Properties Acquired (Details) - USD ($) $ in Thousands	1 Months Ended									9 Months Ended	12 Months Ended
	Jun. 30, 2019	Mar. 30, 2019	Feb. 28, 2019	Nov. 30, 2018	Sep. 30, 2018	Aug. 31, 2018	Jul. 31, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Dec. 31, 2018	Sep. 29, 2018
Business Acquisition [Line Items]
Acquisition-related costs										$ 100	$ 200
Permian Basin
Business Acquisition [Line Items]
Proved	$ 527	$ 24	$ 173	$ 1,166	$ 1,176	$ 5,000	$ 4,349	$ 883	$ 984	724	13,558
Unproved	3,268	0	8,437	0	0	34,673	7,944	13,688	21,452	11,705	77,757
Net Working Capital	0	0	1	0	0	74	215	8	133	1	430
Total Fair Value	3,795	24	8,611	1,166	1,176	39,747	12,508	14,579	22,569	12,430	91,745
Consideration Paid	$ 3,795	$ 24	$ 8,611	1,166		26,461	3,764	14,579	22,569	$ 12,430	69,715	$ 1,176
Fair Value of Common Units Issued				$ 0	$ 0	$ 13,286	$ 8,744	$ 0	$ 0		$ 22,030

Oil and Natural Gas Propertie_3

Oil and Natural Gas Properties - Additional Information (Details) $ in Thousands	Nov. 21, 2017well	Feb. 21, 2017phasewell	Mar. 31, 2019USD ($)	Sep. 30, 2018USD ($)	Jun. 30, 2018USD ($)	Mar. 31, 2018USD ($)	Sep. 30, 2019USD ($)	Dec. 31, 2018USD ($)
Business Acquisition [Line Items]
Business combination, consideration transferred							$ 43,900	$ 149,900
Acquisition-related costs							100	200
Issuance of common units, net of offering costs			$ (43)	$ 29,302	$ 8,929	$ 138
East Texas
Business Acquisition [Line Items]
Payments to acquire oil, mineral, and royalty interests							31,500	58,200
2019 Acquisitions
Business Acquisition [Line Items]
Payments to acquire oil, mineral, and royalty interests							30,600
Issuance of common units, net of offering costs							900
2018 Acquisitions
Business Acquisition [Line Items]
Payments to acquire oil, mineral, and royalty interests								57,600
Issuance of common units, net of offering costs								600
Payments to noncontrolling interests								1,700
Angelina County, Texas | Farmout Agreement
Business Acquisition [Line Items]
Business combination, ownership interest, acreage, percent		50.00%
Exploratory wells, expected to be drilled | well		20
Exploratory wells, additional wells to be drilled | well		20
Asset acquisition, number of phases | phase		3
Canaan Resource Partners | Angelina County, Texas | Farmout Agreement
Business Acquisition [Line Items]
Asset acquisition, term of phase		2 years
Asset acquisition, funding requirements, drilling and completion costs, percent		80.00%
Asset acquisition, ownership interest in wells, percent		80.00%
Asset acquisition, ownership interest, gross, percent		40.00%
Asset acquisition, third phase, ownership interest in additional wells, percent		40.00%
Asset acquisition, third phase, ownership interest in additional wells, gross, percent		20.00%
Asset acquisition, third phase, funding requirements, drilling and completion costs, percent		40.00%
Business combination, pro forma information, revenue of acquiree since acquisition date, actual							89,700
Pivotal | San Augustine County, Texas | Farmout Agreement
Business Acquisition [Line Items]
Exploratory wells, expected to be drilled | well	80
Asset acquisition, ownership interest, gross, percent	10.00%
Asset acquisition, ownership interest, in wells operated by others, percent	100.00%
Business combination, pro forma information, revenue of acquiree since acquisition date, actual							114,500
Other long-term liabilities | Canaan Resource Partners | Angelina County, Texas | Farmout Agreement
Business Acquisition [Line Items]
Business combination, pro forma information, working interests in wells drilled and completed, actual							900	11,600
Other long-term liabilities | Pivotal | San Augustine County, Texas | Farmout Agreement
Business Acquisition [Line Items]
Business combination, pro forma information, working interests in wells drilled and completed, actual							$ 400	$ 41,200
Minimum | Pivotal | San Augustine County, Texas | Farmout Agreement
Business Acquisition [Line Items]
Asset acquisition, ownership interest, in wells operated by others, gross, percent	12.50%
Maximum | Pivotal | San Augustine County, Texas | Farmout Agreement
Business Acquisition [Line Items]
Asset acquisition, ownership interest, in wells operated by others, gross, percent	25.00%

Commodity Derivative Financia_3

Commodity Derivative Financial Instruments - Additional Information (Details)	Sep. 30, 2019counterparty
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Number of counterparties	9

Commodity Derivative Financia_4

Commodity Derivative Financial Instruments - Summary of Fair Value and Classification of Derivative Instruments (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Derivatives Fair Value [Line Items]
Gross fair value amount	$ 42,979	$ 50,264
Effect of Counterparty Netting, Assets	(967)	(2,226)
Total net carrying value on Balance Sheet, assets	42,012	48,038
Gross Fair Value, Liabilities	967	2,226
Effect of Counterparty Netting, Liabilities	(967)	(2,226)
Total net carrying value on Balance Sheet, liabilities	0	0
Commodity derivative assets
Derivatives Fair Value [Line Items]
Gross fair value amount	33,710	38,746
Effect of Counterparty Netting, Assets	(656)	(776)
Total net carrying value on Balance Sheet, assets	33,054	37,970
Deferred charges and other long-term assets
Derivatives Fair Value [Line Items]
Gross fair value amount	9,269	11,518
Effect of Counterparty Netting, Assets	(311)	(1,450)
Total net carrying value on Balance Sheet, assets	8,958	10,068
Commodity derivative liabilities
Derivatives Fair Value [Line Items]
Gross Fair Value, Liabilities	656	776
Effect of Counterparty Netting, Liabilities	(656)	(776)
Total net carrying value on Balance Sheet, liabilities	0	0
Commodity derivative liabilities
Derivatives Fair Value [Line Items]
Gross Fair Value, Liabilities	311	1,450
Effect of Counterparty Netting, Liabilities	(311)	(1,450)
Total net carrying value on Balance Sheet, liabilities	$ 0	$ 0

Commodity Derivative Financia_5

Commodity Derivative Financial Instruments - Changes in Fair Value of Company's Commodity Derivative Instruments (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Derivatives not designated as hedging instruments
Gain (loss) on commodity derivative instruments	$ 24,290	$ (18,514)	$ 12,294	$ (68,194)
Net cash paid (received) on settlements of derivative instruments			(18,320)	20,461
Not Designated as Hedging Instrument
Derivatives not designated as hedging instruments
Beginning fair value of commodity derivative instruments	31,368	(44,043)	48,038	(5,028)
Net change in fair value of commodity derivative instruments	10,644	(8,718)	(6,026)	(47,733)
Ending fair value of commodity derivative instruments	42,012	(52,761)	42,012	(52,761)
Not Designated as Hedging Instrument | Oil
Derivatives not designated as hedging instruments
Gain (loss) on commodity derivative instruments	18,132	(18,830)	(13,224)	(63,325)
Net cash paid (received) on settlements of derivative instruments	(2,938)	11,280	(5,748)	25,809
Not Designated as Hedging Instrument | Natural gas and natural gas liquids sales
Derivatives not designated as hedging instruments
Gain (loss) on commodity derivative instruments	6,158	316	25,518	(4,869)
Net cash paid (received) on settlements of derivative instruments	$ (10,708)	$ (1,484)	$ (12,572)	$ (5,348)

Commodity Derivative Financia_6

Commodity Derivative Financial Instruments - Summary of Open Derivative Contracts for Oil and Natural Gas (Details) - Not Designated as Hedging Instrument bbl in Thousands, MMBTU in Thousands	9 Months Ended
	Sep. 30, 2019MMBTU$ / bbl$ / MMBTUbbl
Swaps Contract | Third Quarter 2019 | Oil | Swap
Derivative [Line Items]
Derivative Contract, Volume (in Bbl) | bbl	285
Derivative Contract, Weighted Average Price (in USD per Bbl or MMBtu)	58.37
Derivative Contract, Price Range Low (in USD per Bbl or MMBtu)	52.82
Derivative Contract, Price Range High (in USD per Bbl or MMBtu)	63.75
Swaps Contract | Fourth Quarter 2019 | Oil | Swap
Derivative [Line Items]
Derivative Contract, Volume (in Bbl) | bbl	936
Derivative Contract, Weighted Average Price (in USD per Bbl or MMBtu)	58.50
Derivative Contract, Price Range Low (in USD per Bbl or MMBtu)	52.82
Derivative Contract, Price Range High (in USD per Bbl or MMBtu)	63.75
Swaps Contract | Fourth Quarter 2019 | Natural gas and natural gas liquids sales | Swap
Derivative [Line Items]
Derivative Contract, Volume (in MMBtu) | MMBTU	14,640
Derivative Contract, Weighted Average Price (in USD per Bbl or MMBtu) | $ / MMBTU	2.96
Derivative Contract, Price Range Low (in USD per Bbl or MMBtu) | $ / MMBTU	2.81
Derivative Contract, Price Range High (in USD per Bbl or MMBtu) | $ / MMBTU	3.20
Swaps Contract | First Quarter 2020 | Oil | Swap
Derivative [Line Items]
Derivative Contract, Volume (in Bbl) | bbl	510
Derivative Contract, Weighted Average Price (in USD per Bbl or MMBtu)	57.14
Derivative Contract, Price Range Low (in USD per Bbl or MMBtu)	54.92
Derivative Contract, Price Range High (in USD per Bbl or MMBtu)	58.65
Swaps Contract | First Quarter 2020 | Natural gas and natural gas liquids sales | Swap
Derivative [Line Items]
Derivative Contract, Volume (in MMBtu) | MMBTU	10,010
Derivative Contract, Weighted Average Price (in USD per Bbl or MMBtu) | $ / MMBTU	2.69
Derivative Contract, Price Range Low (in USD per Bbl or MMBtu) | $ / MMBTU	2.55
Derivative Contract, Price Range High (in USD per Bbl or MMBtu) | $ / MMBTU	2.74
Swaps Contract | Second Quarter 2020 | Oil | Swap
Derivative [Line Items]
Derivative Contract, Volume (in Bbl) | bbl	510
Derivative Contract, Weighted Average Price (in USD per Bbl or MMBtu)	57.14
Derivative Contract, Price Range Low (in USD per Bbl or MMBtu)	54.92
Derivative Contract, Price Range High (in USD per Bbl or MMBtu)	58.65
Swaps Contract | Second Quarter 2020 | Natural gas and natural gas liquids sales | Swap
Derivative [Line Items]
Derivative Contract, Volume (in MMBtu) | MMBTU	10,010
Derivative Contract, Weighted Average Price (in USD per Bbl or MMBtu) | $ / MMBTU	2.69
Derivative Contract, Price Range Low (in USD per Bbl or MMBtu) | $ / MMBTU	2.55
Derivative Contract, Price Range High (in USD per Bbl or MMBtu) | $ / MMBTU	2.74
Swaps Contract | Third Quarter 2020 | Oil | Swap
Derivative [Line Items]
Derivative Contract, Volume (in Bbl) | bbl	510
Derivative Contract, Weighted Average Price (in USD per Bbl or MMBtu)	57.14
Derivative Contract, Price Range Low (in USD per Bbl or MMBtu)	54.92
Derivative Contract, Price Range High (in USD per Bbl or MMBtu)	58.65
Swaps Contract | Third Quarter 2020 | Natural gas and natural gas liquids sales | Swap
Derivative [Line Items]
Derivative Contract, Volume (in MMBtu) | MMBTU	10,120
Derivative Contract, Weighted Average Price (in USD per Bbl or MMBtu) | $ / MMBTU	2.69
Derivative Contract, Price Range Low (in USD per Bbl or MMBtu) | $ / MMBTU	2.55
Derivative Contract, Price Range High (in USD per Bbl or MMBtu) | $ / MMBTU	2.74
Swaps Contract | Fourth Quarter 2020 | Oil | Swap
Derivative [Line Items]
Derivative Contract, Volume (in Bbl) | bbl	510
Derivative Contract, Weighted Average Price (in USD per Bbl or MMBtu)	57.14
Derivative Contract, Price Range Low (in USD per Bbl or MMBtu)	54.92
Derivative Contract, Price Range High (in USD per Bbl or MMBtu)	58.65
Swaps Contract | Fourth Quarter 2020 | Natural gas and natural gas liquids sales | Swap
Derivative [Line Items]
Derivative Contract, Volume (in MMBtu) | MMBTU	10,120
Derivative Contract, Weighted Average Price (in USD per Bbl or MMBtu) | $ / MMBTU	2.69
Derivative Contract, Price Range Low (in USD per Bbl or MMBtu) | $ / MMBTU	2.55
Derivative Contract, Price Range High (in USD per Bbl or MMBtu) | $ / MMBTU	2.74
Collar Contract | Third Quarter 2019 | Oil | Collar
Derivative [Line Items]
Derivative Contract, Volume (in Bbl) | bbl	20
Derivative Contract, Price Range Low (in USD per Bbl or MMBtu)	65
Derivative Contract, Price Range High (in USD per Bbl or MMBtu)	74
Collar Contract | Fourth Quarter 2019 | Oil | Collar
Derivative [Line Items]
Derivative Contract, Volume (in Bbl) | bbl	60
Derivative Contract, Price Range Low (in USD per Bbl or MMBtu)	65
Derivative Contract, Price Range High (in USD per Bbl or MMBtu)	74
Collar Contract | First Quarter 2020 | Oil | Collar
Derivative [Line Items]
Derivative Contract, Volume (in Bbl) | bbl	210
Derivative Contract, Price Range Low (in USD per Bbl or MMBtu)	56.43
Derivative Contract, Price Range High (in USD per Bbl or MMBtu)	67.14
Collar Contract | Second Quarter 2020 | Oil | Collar
Derivative [Line Items]
Derivative Contract, Volume (in Bbl) | bbl	210
Derivative Contract, Price Range Low (in USD per Bbl or MMBtu)	56.43
Derivative Contract, Price Range High (in USD per Bbl or MMBtu)	67.14
Collar Contract | Third Quarter 2020 | Oil | Collar
Derivative [Line Items]
Derivative Contract, Volume (in Bbl) | bbl	210
Derivative Contract, Price Range Low (in USD per Bbl or MMBtu)	56.43
Derivative Contract, Price Range High (in USD per Bbl or MMBtu)	67.14
Collar Contract | Fourth Quarter 2020 | Oil | Collar
Derivative [Line Items]
Derivative Contract, Volume (in Bbl) | bbl	210
Derivative Contract, Price Range Low (in USD per Bbl or MMBtu)	56.43
Derivative Contract, Price Range High (in USD per Bbl or MMBtu)	67.14

Fair Value Measurements - Sched

Fair Value Measurements - Schedule of Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Gross fair value amount	$ 42,979	$ 50,264
Effect of Counterparty Netting, Assets	(967)	(2,226)
Total net carrying value on Balance Sheet, assets	42,012	48,038
Gross Fair Value, Liabilities	967	2,226
Effect of Counterparty Netting, Liabilities	(967)	(2,226)
Total net carrying value on Balance Sheet, liabilities	0	0
Commodity Derivative Instruments | Fair Value Measurements, Recurring Basis
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Effect of Counterparty Netting, Assets	(967)	(2,226)
Total net carrying value on Balance Sheet, assets	42,012	48,038
Effect of Counterparty Netting, Liabilities	(967)	(2,226)
Total net carrying value on Balance Sheet, liabilities	0	0
Commodity Derivative Instruments | Fair Value Measurements, Recurring Basis | Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Gross fair value amount	0	0
Gross Fair Value, Liabilities	0	0
Commodity Derivative Instruments | Fair Value Measurements, Recurring Basis | Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Gross fair value amount	42,979	50,264
Gross Fair Value, Liabilities	967	2,226
Commodity Derivative Instruments | Fair Value Measurements, Recurring Basis | Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Gross fair value amount	0	0
Gross Fair Value, Liabilities	$ 0	$ 0

Credit Facility (Details)

Credit Facility (Details) - USD ($)	Oct. 31, 2018	Sep. 30, 2019	Oct. 30, 2018	Oct. 23, 2019	Dec. 31, 2018	May 04, 2018	Apr. 25, 2017
Line Of Credit Facility [Line Items]
Credit facility		$ 413,000,000			$ 410,000,000
Senior Line of Credit | Revolving Credit Facility
Line Of Credit Facility [Line Items]
Maximum borrowing capacity		$ 1,000,000,000
Borrowing base	$ 675,000,000					$ 600,000,000	$ 550,000,000
Weighted average interest rate (percent)		4.30%			4.76%
Interest payable, term		90 days
Borrowing base threshold (percent)		50.00%
Credit facility		$ 413,000,000			$ 410,000,000
Unused portion of current borrowing base		$ 262,000,000			$ 265,000,000
Senior Line of Credit | Revolving Credit Facility | Subsequent Event
Line Of Credit Facility [Line Items]
Borrowing base				$ 650,000,000
Senior Line of Credit | Revolving Credit Facility | Federal Funds
Line Of Credit Facility [Line Items]
Interest rate (percent)		0.50%
Senior Line of Credit | Revolving Credit Facility | LIBOR Plus Margin Rate
Line Of Credit Facility [Line Items]
Interest rate (percent)		1.00%
Senior Line of Credit | Revolving Credit Facility | Borrowing Base Utilization Percentage Less Than 50%
Line Of Credit Facility [Line Items]
Commitment fee payable rate (percent)		0.375%
Senior Line of Credit | Revolving Credit Facility | Borrowing Base Utilization Percentage Equal to or Greater Than 50%
Line Of Credit Facility [Line Items]
Commitment fee payable rate (percent)		0.50%
Senior Line of Credit | Revolving Credit Facility | Minimum
Line Of Credit Facility [Line Items]
Interest payable, term		90 days
Current ratio		1
Senior Line of Credit | Revolving Credit Facility | Minimum | LIBOR Plus Margin Rate
Line Of Credit Facility [Line Items]
Interest rate (percent)	1.75%		2.00%
Senior Line of Credit | Revolving Credit Facility | Minimum | Prime Rate Plus Margin Rate
Line Of Credit Facility [Line Items]
Interest rate (percent)	0.75%		1.00%
Senior Line of Credit | Revolving Credit Facility | Maximum
Line Of Credit Facility [Line Items]
Ratio of total debt to EBITDAX		3.5
Senior Line of Credit | Revolving Credit Facility | Maximum | LIBOR Plus Margin Rate
Line Of Credit Facility [Line Items]
Interest rate (percent)	2.75%		3.00%
Senior Line of Credit | Revolving Credit Facility | Maximum | Prime Rate Plus Margin Rate
Line Of Credit Facility [Line Items]
Interest rate (percent)	1.75%		2.00%

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Details)	Sep. 30, 2019	Nov. 28, 2017
Samedan
Business Acquisition [Line Items]
Business acquisition, percentage of voting interests acquired		100.00%
Comin
Business Acquisition [Line Items]
Business acquisition, percentage of voting interests acquired		100.00%
Noncontrolling interest, ownership percentage by noncontrolling owners	45.33%
Temin
Business Acquisition [Line Items]
Noncontrolling interest, ownership percentage by noncontrolling owners	42.63%

Incentive Compensation - Summar

Incentive Compensation - Summary of Incentive Compensation Expense (Details) - General and administrative expenses - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Cash—short and long-term incentive plans	$ 1,092	$ 4,366	$ 4,336	$ 7,568
Incentive compensation expense	4,958	13,962	21,242	32,515
Restricted common and subordinated units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity-based compensation	2,552	3,404	8,162	10,180
Restricted Performance Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity-based compensation	727	5,611	6,984	13,026
Common Units | Board of Directors
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Incentive compensation expense	$ 587	$ 581	$ 1,760	$ 1,741

Preferred Units (Details)

Preferred Units (Details) - USD ($) $ / shares in Units, $ in Thousands	Nov. 28, 2017	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Preferred Units
Class of Stock [Line Items]
Partners' equity, preferred units, outstanding (in shares)		0		0
Preferred units distribution rate		10.00%
Adjusted conversion price (in us dollars per share)		$ 14.2683
Number of preferred units redeemed		2,115
Preferred stock, redemption amount			$ 2,100
Number of preferred units converted (in shares)			24,248
Conversion of preferred units to common units			$ 24,200
Common Units
Class of Stock [Line Items]
Adjusted conversion rate		30.3431
Conversion of preferred units (in shares)			735,758
Number of shares issued (in shares)		0	2,121,643
Subordinated Units
Class of Stock [Line Items]
Adjusted conversion rate		39.7427
Conversion of preferred units (in shares)			963,681
Series B Cumulative Convertible Preferred Units
Class of Stock [Line Items]
Partners' equity, preferred units, outstanding (in shares)		14,711,000		14,711,000
Preferred units distribution rate		7.00%
Shares, price per share (in dollars per share)	$ 20.3926
Proceeds from issuance of convertible preferred stock	$ 300,000
Minimum underlying value for conversion trigger		$ 10,000
Preferred units, outstanding value		298,361		$ 298,361
Accrued distributions		$ 5,300		$ 5,300
Series B Cumulative Convertible Preferred Units | Noble Acquisition
Class of Stock [Line Items]
Number of shares issued (in shares)	14,711,219

Earnings Per Unit - Additional

Earnings Per Unit - Additional Information (Details) - shares	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Number of performance units award included in calculation of diluted EPU		0	0	0
Restricted performance unit awards
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Number of performance units award included in calculation of diluted EPU	0	0	0	0

Earnings Per Unit - Computation

Earnings Per Unit - Computation of Basic and Diluted Earnings per Unit (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Earnings Per Share Basic [Line Items]
Net income (loss)	$ 70,247	$ 60,775	$ 174,351	$ 131,422
Net (income) loss attributable to noncontrolling interests	0	(22)	0	(1)
Distributions on Series A redeemable preferred units	0	0	0	(25)
Distributions on Series B cumulative convertible preferred units	(5,250)	(5,250)	(15,750)	(15,750)
NET INCOME (LOSS) ATTRIBUTABLE TO THE GENERAL PARTNER AND COMMON AND SUBORDINATED UNITS	64,997	55,503	158,601	115,646
ALLOCATION OF NET INCOME (LOSS):
General partner interest	0	0	0	0
NET INCOME (LOSS) ATTRIBUTABLE TO THE GENERAL PARTNER AND COMMON AND SUBORDINATED UNITS	64,997	$ 55,503	$ 158,601	$ 115,646
NET INCOME (LOSS) ATTRIBUTABLE TO LIMITED PARTNERS PER COMMON AND SUBORDINATED UNIT:
Effect of dilutive securities (in shares)		0	0	0
Common Units
ALLOCATION OF NET INCOME (LOSS):
Allocation of net income (loss)	$ 64,997	$ 29,188	$ 134,608	$ 71,037
NET INCOME (LOSS) ATTRIBUTABLE TO LIMITED PARTNERS PER COMMON AND SUBORDINATED UNIT:
Weighted average units outstanding (basic) (in shares)	205,957	106,706	155,513	105,254
Effect of dilutive securities (in shares)	0	0	0	0
Weighted average units outstanding (diluted) (in shares)	205,957	106,706	155,513	105,254
Per unit (basic) (in dollars per share)	$ 0.32	$ 0.27	$ 0.87	$ 0.67
Per unit (diluted) (in dollars per share)	$ 0.32	$ 0.27	$ 0.87	$ 0.67
Subordinated Units
ALLOCATION OF NET INCOME (LOSS):
Allocation of net income (loss)	$ 0	$ 26,315	$ 23,993	$ 44,609
NET INCOME (LOSS) ATTRIBUTABLE TO LIMITED PARTNERS PER COMMON AND SUBORDINATED UNIT:
Weighted average units outstanding (basic) (in shares)	0	96,329	50,458	96,021
Effect of dilutive securities (in shares)	0	0	0	0
Weighted average units outstanding (diluted) (in shares)	0	96,329	50,458	96,021
Per unit (basic) (in dollars per share)	$ 0	$ 0.27	$ 0.48	$ 0.46
Per unit (diluted) (in dollars per share)	$ 0	$ 0.27	$ 0.48	$ 0.46

Earnings Per Unit - Potentially

Earnings Per Unit - Potentially Dilutive Securities Excluded from the Computation of Diluted Weighted Average Shares Outstanding (Details) - shares shares in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Common Units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Units issuable upon conversion of preferred units excluded from the calculation of diluted EPU	14,969	14,969	14,969	15,158
Series A redeemable preferred units on an as-converted basis | Common Units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Units issuable upon conversion of preferred units excluded from the calculation of diluted EPU	0	0	0	189
Series A redeemable preferred units on an as-converted basis | Subordinated Units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Units issuable upon conversion of preferred units excluded from the calculation of diluted EPU	0	0	0	247
Series B cumulative convertible preferred units on an as-converted basis | Common Units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Units issuable upon conversion of preferred units excluded from the calculation of diluted EPU	14,969	14,969	14,969	14,969

Common and Subordinated Units_2

Common and Subordinated Units (Details) - USD ($)	9 Months Ended		25 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Jun. 30, 2019	May 24, 2019	Mar. 31, 2019	Dec. 31, 2018	Nov. 05, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	May 26, 2017
Class of Stock [Line Items]
Partners' capital account, distribution amount per share (in dollars per share)			$ 1.35
Stock repurchase program, authorized amount							$ 75,000,000
Proceeds from issuance of common units, net of offering costs	$ (43,000)	$ 38,369,000
Series B Cumulative Convertible Preferred Units
Class of Stock [Line Items]
Preferred units minimum voting rights rate (percent)	15.00%
Preferred units distribution rate	7.00%
Common Units
Class of Stock [Line Items]
Partners' capital account, units	205,952,000	108,330,000	205,956,000		109,377,000	108,363,000		105,494,000	104,926,000	103,456,000
Treasury stock, acquired (in shares)	136,665,000,000
Treasury stock, value, acquired, cost method	$ 2,200,000
Equity distribution agreement, maximum value											$ 100,000,000
Number of shares issued (in shares)	0	2,121,643
Proceeds from issuance of common units, net of offering costs		$ 38,400,000	$ 73,000,000
Common Units | November 2018 Repurchase Program
Class of Stock [Line Items]
Treasury stock, value, acquired, cost method	$ 4,200,000
Subordinated Units
Class of Stock [Line Items]
Partners' capital account, units				96,328,836
Common Units
Class of Stock [Line Items]
Partners' capital account, units				96,328,836

Common and Subordinated Units -

Common and Subordinated Units - Per share distributions to common and subordinated unitholders (Details) - $ / shares	3 Months Ended		6 Months Ended	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Jun. 30, 2019	Sep. 30, 2019	Sep. 30, 2018
Common Units
Class of Stock [Line Items]
Per unit (in usd per share)	$ 0.3700	$ 0.3375		$ 1.1100	$ 0.9625
Subordinated Units
Class of Stock [Line Items]
Per unit (in usd per share)	$ 0	$ 0.3375	$ 0.7400		$ 0.7550

Subsequent Events (Details)

Subsequent Events (Details)	Oct. 23, 2019$ / shares
Subsequent Event | Common Units
Subsequent Event [Line Items]
Quarterly cash distribution declared (in usd per unit)	$ 0.37