Financial Instruments (Schedule of Long-Term Debt) (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Debt Instrument [Line Items]
Long-term debt	$ 384,002	$ 398,009
Less: current portion	(2)	(9)
Long-term debt, net of current portion	384,000	398,000
Long-term Debt
Debt Instrument [Line Items]
Long-term debt	$ 2	$ 9
Interest rate, effective percentage	5.50%	5.50%
Line of Credit
Debt Instrument [Line Items]
Long-term debt	$ 384,000	$ 398,000
Interest rate, effective percentage	3.56%	3.50%