Preferred Units - Additional Information (Details) $ / shares in Units, $ in Thousands				12 Months Ended
	Nov. 28, 2017 USD ($) $ / shares	May 05, 2016	Nov. 06, 2015 USD ($) $ / shares shares	Dec. 31, 2017 USD ($) $ / shares shares	Dec. 31, 2016 USD ($) shares	Dec. 31, 2015 USD ($) shares	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)
Class of Stock [Line Items]
Partners' equity — Series A redeemable preferred units, 26 and 53 units outstanding at December 31, 2017 and 2016, respectively				$ 322,422	$ 54,015		$ 27,092	$ 27,085	$ 34,145	$ 54,015	$ 54,001	$ 54,001
Proceeds from issuance of Series B cumulative convertible preferred units of Black Stone Minerals, L.P., net of offering costs				$ 293,469	$ 0	$ 0
Preferred Units
Class of Stock [Line Items]
Partners' equity, preferred units, outstanding (in units) | shares				26,363	52,691
Partners' equity — Series A redeemable preferred units, 26 and 53 units outstanding at December 31, 2017 and 2016, respectively				$ 27,000	$ 54,000
Accrued distributions				$ 700	$ 1,300
Preferred units distribution rate (percent)				10.00%
Unpaid preferred yield (percent)		100.00%
Preferred yield (percent)				10.00%
Adjusted conversion price (in usd per share) | $ / shares				$ 14.2683
Number of preferred units redeemed | shares				19,704	18,461
Amount of preferred stock redeemed				$ 20,200	$ 19,000
Number of preferred units converted | shares				6,624	6,064
Conversion of preferred units to common units				$ 6,600	$ 6,100	$ 39,200
Conversion of stock, shares converted | shares						39,240
Maximum percentage of preferred units repurchase			100.00%
Purchased and cancelled redeemable preferred units | shares			40,747
Cost of purchased and cancelled redeemable preferred units, per unit | $ / shares			$ 1,019.45
Purchased and cancelled redeemable preferred units, total cost			$ 41,500
Common and Subordinated Units
Class of Stock [Line Items]
Aggregate unpaid preferred yield (percent)		100.00%
Interest fair market value (percent)		10.00%
Common Units
Class of Stock [Line Items]
Convertible preferred units conversion ratio				30.3431
Conversion of preferred units | shares				200,996	184,006	1,190,664
Number of shares issued | shares				2,000,000
Subordinated Units
Class of Stock [Line Items]
Convertible preferred units conversion ratio				39.7427
Conversion of preferred units | shares				263,247	240,986	1,559,502
Series B Cumulative Convertible Preferred Units
Class of Stock [Line Items]
Partners' equity — Series A redeemable preferred units, 26 and 53 units outstanding at December 31, 2017 and 2016, respectively				$ 295,394	$ 0
Accrued distributions				$ 1,900
Preferred units distribution rate (percent)				7.00%
Shares, price per share (in dollars per share) | $ / shares	$ 20.3926
Proceeds from issuance of Series B cumulative convertible preferred units of Black Stone Minerals, L.P., net of offering costs	$ 300,000
Minimum underlying value for conversion trigger				$ 10,000