Fair Value Measurements (Summary Of Financial Assets And Liabilities Accounted For At Fair Value) (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Assets:
Investments in marketable securities	$ 164,664	$ 162,797
Derivatives	6,249
Total assets	170,913
Liabilities:
Derivatives	0	$ 13,288
Level 1
Assets:
Investments in marketable securities	94,607
Derivatives	3,063
Total assets	97,670
Liabilities:
Derivatives	0
Level 2
Assets:
Investments in marketable securities	70,057
Derivatives	2,335
Total assets	72,392
Liabilities:
Derivatives	0
Level 3
Assets:
Investments in marketable securities	0
Derivatives	851
Total assets	851
Liabilities:
Derivatives	$ 0