CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Jun. 30, 2026	Dec. 31, 2025
CURRENT ASSETS
Cash and cash equivalents	$ 1,674	$ 1,478
Accrued revenue and accounts receivable	71,060	65,572
Commodity derivative assets, net	9,848	18,864
Prepaid expenses and other current assets	6,425	9,722
TOTAL CURRENT ASSETS	89,007	95,636
PROPERTY AND EQUIPMENT
Oil and natural gas properties, at cost, using the successful efforts method of accounting, includes unproved properties of $1,099,220 and $1,063,709 at June 30, 2026 and December 31, 2025, respectively	3,134,600	3,079,340
Accumulated depreciation, depletion, amortization and impairment	(1,874,181)	(1,855,332)
Oil and natural gas properties, net	1,260,419	1,224,008
Other property and equipment, net of accumulated depreciation of $16,229 and $15,768 at June 30, 2026 and December 31, 2025, respectively	1,020	1,126
NET PROPERTY AND EQUIPMENT	1,261,439	1,225,134
DEFERRED CHARGES AND OTHER LONG-TERM ASSETS	15,465	14,784
TOTAL ASSETS	1,365,911	1,335,554
CURRENT LIABILITIES
Accounts payable	4,133	2,823
Accrued liabilities	12,111	19,388
Commodity derivative liabilities, net	5,823	0
Other current liabilities	1,627	2,412
TOTAL CURRENT LIABILITIES	23,694	24,623
LONG–TERM LIABILITIES
Credit facility	196,000	154,000
Accrued incentive compensation	841	1,011
Commodity derivative liabilities, net	3,072	0
Asset retirement obligations	23,312	22,716
Other long-term liabilities	5,526	4,748
TOTAL LIABILITIES	252,445	207,098
COMMITMENTS AND CONTINGENCIES (Note 7)
EQUITY
Partners' equity – general partner interest	0	0
TOTAL EQUITY	812,988	827,978
TOTAL LIABILITIES, MEZZANINE EQUITY, AND EQUITY	1,365,911	1,335,554
Preferred Units
MEZZANINE EQUITY
Partners' equity – Series B cumulative convertible preferred units, 14,711 units outstanding at June 30, 2026 and December 31, 2025, respectively	300,478	300,478
Common units
EQUITY
Partners' equity – common units, 212,703 and 211,873 units outstanding at June 30, 2026 and December 31, 2025, respectively	$ 812,988	$ 827,978

Contract With Customer, Asset And Accounts Receivable, After Allowance For Credit Loss, Current

No definition available.

Name:	bsm_ContractWithCustomerAssetAndAccountsReceivableAfterAllowanceForCreditLossCurrent
Namespace Prefix:	bsm_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Carrying value as of the balance sheet date of liabilities incurred (and for which invoices have typically been received) and payable to vendors for goods and services received that are used in an entity's business. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer).