Condensed Consolidated Statements of Income and Total Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Revenues:
Total revenues	$ 123,693	$ 74,383	$ 303,780	$ 228,260
Expenses:
Salaries and related employee expenses	8,542	7,678	31,792	27,235
Water service-related expenses	3,650	2,260	10,499	11,205
General and administrative expenses	2,844	1,883	8,491	7,290
Legal and professional fees	1,551	1,987	4,904	6,955
Land sales expenses	0	67	0	2,773
Depreciation, depletion and amortization	3,866	3,760	11,562	10,773
Total operating expenses	20,453	17,635	67,248	66,231
Operating income	103,240	56,748	236,532	162,029
Other income, net	513	1,287	924	2,296
Income before income taxes	103,753	58,035	237,456	164,325
Income tax expense	19,916	11,760	46,521	33,067
Net income	83,837	46,275	190,935	131,258
Other comprehensive income — periodic pension costs, net of income taxes of $8, $4, $23 and $11, respectively	29	13	86	40
Total comprehensive income	$ 83,866	$ 46,288	$ 191,021	$ 131,298
Weighted average number of Sub-share Certificates outstanding, basic (in shares)	7,751,329	7,756,156	7,754,439	7,756,156
Weighted average number of Sub-share Certificates outstanding, diluted (in shares)	7,751,329	7,756,156	7,754,439	7,756,156
Net income per Sub-share Certificate — basic (in dollars per share)	$ 10.82	$ 5.97	$ 24.62	$ 16.92
Net income per Sub-share Certificate — diluted (in dollars per share)	10.82	5.97	24.62	16.92
Cash dividends per Sub-share Certificate (in dollars per share)	$ 2.75	$ 0	$ 8.25	$ 16.00
Oil and gas royalties
Revenues:
Total revenues	$ 79,098	$ 31,758	$ 186,835	$ 94,631
Water sales
Revenues:
Total revenues	19,554	12,139	44,983	47,525
Produced water royalties
Revenues:
Total revenues	15,140	12,246	43,147	37,863
Easements and other surface-related income
Revenues:
Total revenues	9,832	6,690	27,856	32,107
Land sales
Revenues:
Total revenues	0	11,463	746	15,855
Other operating revenue
Revenues:
Total revenues	$ 69	$ 87	$ 213	$ 279