Financial Instruments (Schedule of Long-Term Debt) (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Long-term debt	$ 435,017	$ 424,029
Less: current portion	(17)	(20)
Long-term debt, net of current portion	435,000	424,009
Line of Credit [Member]
Debt Instrument [Line Items]
Long-term debt	$ 435,000	$ 424,000
Interest rate	3.11%	3.43%
Maturity date range, end	Dec. 31, 2022
Long-term Debt [Member]
Debt Instrument [Line Items]
Long-term debt	$ 17	$ 29
Interest rate	5.50%	5.50%
Maturity date range, end	Dec. 31, 2021