Consolidated Statements of Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Revenues
Revenues	$ 160,704	$ 158,277	$ 144,435
Cost of revenues
Labor and other operating expenses	93,738	99,207	96,558
Depreciation, depletion and amortization	19,379	17,394	17,391
Total cost of revenues	113,117	116,601	113,949
Gross profit	47,587	41,676	30,486
Selling, general and administrative expenses	12,168	11,500	10,484
Impairment of long-lived assets	1,550	930
Operating profit	33,869	29,246	20,002
Other expense (income)
Interest expense	248	244	243
Interest and other income, net	(451)	(1,898)	(1,809)
Total other expense (income)	(203)	(1,654)	(1,566)
Income before income tax expense	34,072	30,900	21,568
Income tax expense	5,849	4,844	1,883
Net income	$ 28,223	$ 26,056	$ 19,685
Net income per share of common stock
Basic (in dollars per share)	$ 5.01	$ 4.64	$ 3.52
Diluted (in dollars per share)	$ 5.00	$ 4.64	$ 3.51