Long-Term Debt (Schedule of Long-Term Debt) (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Total debt
Long-term Debt, Total	$ 10,000	$ 10,000
Amounts payable within one year	0	0
Long-term debt, noncurrent	10,000	10,000	[1]
Revolving Credit Facility [Member]
Total debt
Long-term Debt, Total	$ 10,000	$ 10,000

[1] The balance sheet at December 31, 2020 has been derived from the audited financial statements at that date but does not include all of the information and footnotes required by accounting principles generally accepted in the United States for complete financial statements.