Fair Value Measurements (Summary Of Financial Assets And Liabilities Accounted For At Fair Value) (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Assets:
Investments in marketable securities	$ 162,530	$ 155,846
Derivatives	11,284
Total assets	173,814
Liabilities:
Derivatives	36,555	$ 7,217
Level 1
Assets:
Investments in marketable securities	99,575
Derivatives	0
Total assets	99,575
Liabilities:
Derivatives	34,838
Level 2
Assets:
Investments in marketable securities	62,955
Derivatives	5,044
Total assets	67,999
Liabilities:
Derivatives	709
Level 3
Assets:
Investments in marketable securities	0
Derivatives	6,240
Total assets	6,240
Liabilities:
Derivatives	$ 1,008