Fair Value Measurements (Summary Of Financial Assets And Liabilities Accounted For At Fair Value) (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Assets:
Investments in marketable securities	$ 67,237	$ 135,667
Derivatives	5,659
Total assets	72,896
Liabilities:
Derivatives	5,066
Level 1
Assets:
Investments in marketable securities	14,054
Derivatives	5,131
Total assets	19,185
Liabilities:
Derivatives	0
Level 2
Assets:
Investments in marketable securities	53,183
Derivatives	495
Total assets	53,678
Liabilities:
Derivatives	5,066
Level 3
Assets:
Investments in marketable securities	0
Derivatives	33
Total assets	33
Liabilities:
Derivatives	$ 0