Properties And Equipment - Summary of Acquisitions (Details) $ in Millions		3 Months Ended
		Sep. 30, 2021 USD ($) a	Jun. 30, 2021 USD ($) a	Dec. 31, 2020 USD ($) a	Dec. 31, 2019 USD ($) a
Haynesville /LA [Member]
Property Plant And Equipment [Line Items]
Net royalty acres | a	[1],[2]	817	262
Purchase Price | $	[2]	$ 7.3	$ 1.3
Haynesville / TX [Member]
Property Plant And Equipment [Line Items]
Net royalty acres | a	[1],[2]		131	142
Purchase Price | $	[2]		$ 1.0	$ 1.0
SCOOP / OK [Member]
Property Plant And Equipment [Line Items]
Net royalty acres | a	[1],[2]		2,514	297	964
Purchase Price | $	[2]		$ 13.0	$ 2.3	$ 9.3
Haynesville / TX [Member]
Property Plant And Equipment [Line Items]
Net royalty acres | a	[1],[2]			184
Purchase Price | $	[2]			$ 0.8
Haynesville / TX [Member]
Property Plant And Equipment [Line Items]
Net royalty acres | a	[1],[2]			386
Purchase Price | $	[2]			$ 3.5

[1] An estimated net royalty equivalent was used for the minerals included in the net royalty acres.

[2] Excludes subsequent closing adjustments and insignificant acquisitions.