Immaterial Correction of an Error in Prior Periods (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Cumulative adjustment to equity	$ 33,737,000	$ 33,532,000	$ 31,513,000
Retained earnings	21,803,000	21,703,000
Accumulated other comprehensive gain (loss)	(1,356,000)	(1,121,000)
Selling, general and administrative	7,998,000	8,883,000
Income tax provision	(38,000)	671,000
Other comprehensive income:
Retirement benefits adjustment, net of income taxes	$ (235,000)	$ (275,000)
Basic net income per share	$ 0.04	$ 1.05
Diluted net income per share	$ 0.04	$ 1.03
As Reported
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Cumulative adjustment to equity			$ 881,000
Retained earnings		$ 20,484,000
Accumulated other comprehensive gain (loss)		98,000
Selling, general and administrative		9,313,000
Income tax provision		579,000
Other comprehensive income:
Retirement benefits adjustment, net of income taxes		$ 63,000
Basic net income per share		$ 0.91
Diluted net income per share		$ 0.88
Restatement
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Retained earnings		$ 1,219,000
Accumulated other comprehensive gain (loss)		(1,219,000)
Selling, general and administrative		(430,000)
Income tax provision		92,000
Other comprehensive income:
Retirement benefits adjustment, net of income taxes		$ (338,000)
Basic net income per share		$ 0.14
Diluted net income per share		$ 0.15