Income Taxes - Schedule of Difference of Income Tax Expense from the United States Federal Income Tax Rates (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Amount
Tax expense at statutory rate	$ 5,427	$ 3,192	$ 7,320
State taxes, net	1,156	852	1,575
Permanent differences	491	244	433
Equity-based compensation benefits	(305)	371	(126)
Post-employment benefits	(67)	345	0
Uncertain tax position	49	93	154
Valuation allowance	287	213	0
Other	(18)	(123)	(69)
Income Tax Expense	$ 7,020	$ 5,187	$ 9,287
Percentage
Tax expense at statutory rate (as a percent)	21.00%	21.00%	21.00%
State taxes, net (as a percent)	4.48%	5.60%	4.51%
Permanent differences (as a percent)	1.90%	1.61%	1.24%
Equity-based compensation benefits (as a percent)	(1.18%)	2.44%	(0.36%)
Post-employment benefits (as a percent)	(0.26%)	2.27%	0.00%
Uncertain tax position (as a percent)	0.19%	0.61%	0.44%
Valuation allowance on capital loss (as a percent)	1.11%	1.40%	0.00%
Other (as a percent)	(0.07%)	(0.80%)	(0.19%)
Total percentage	27.17%	34.13%	26.64%