Fair Value Measurements (Summary Of Financial Assets And Liabilities Accounted For At Fair Value) (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Assets:
Investments in marketable securities	$ 129,057	$ 135,667
Derivatives	5,158
Total assets	134,215
Liabilities:
Derivatives	5,624
Level 1
Assets:
Investments in marketable securities	38,372
Derivatives	4,958
Total assets	43,330
Liabilities:
Derivatives	0
Level 2
Assets:
Investments in marketable securities	90,685
Derivatives	111
Total assets	90,796
Liabilities:
Derivatives	5,624
Level 3
Assets:
Investments in marketable securities	0
Derivatives	89
Total assets	89
Liabilities:
Derivatives	$ 0