Fair Value Measurements (Summary Of Financial Assets And Liabilities Accounted For At Fair Value) (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Assets:
Investments in marketable securities	$ 63,128	$ 135,667
Derivatives	2,665
Total assets	65,793
Liabilities:
Derivatives	4,545
Level 1
Assets:
Investments in marketable securities	15,306
Derivatives	2,560
Total assets	17,866
Liabilities:
Derivatives	0
Level 2
Assets:
Investments in marketable securities	47,822
Derivatives	105
Total assets	47,927
Liabilities:
Derivatives	4,545
Level 3
Assets:
Investments in marketable securities	0
Derivatives	0
Total assets	0
Liabilities:
Derivatives	$ 0