Fair Value Measurements (Summary Of Financial Assets And Liabilities Accounted For At Fair Value) (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Assets:
Investments in marketable securities	$ 160,894	$ 155,846
Derivatives	12,031
Total assets	172,925
Liabilities:
Derivatives	26,069	$ 7,217
Level 1
Assets:
Investments in marketable securities	54,832
Derivatives	593
Total assets	55,425
Liabilities:
Derivatives	24,862
Level 2
Assets:
Investments in marketable securities	106,062
Derivatives	4,786
Total assets	110,848
Liabilities:
Derivatives	638
Level 3
Assets:
Investments in marketable securities	0
Derivatives	6,652
Total assets	6,652
Liabilities:
Derivatives	$ 569