Income Taxes - Reconciliation of Income Tax Expense from Statutory Federal Income Tax Rate (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Difference between total income tax expense and the amount computed by applying the statutory Federal income tax rate to income before taxes:
Income tax at statutory rate	$ 3,058	$ 1,171	$ (1,046)
State income taxes, net of Federal benefit	948	317	(185)
Oil and mineral depletion	(131)	(134)	(180)
Permanent differences	26	19	25
Excess stock compensation expense	(57)	(20)	107
U.S. Tax Reform adjustment	0	0	54
Other	136	(33)	(58)
Provision (benefit) for income taxes	$ 3,980	$ 1,320	$ (1,283)
Effective tax rate	27.30%	23.80%	41.30%