Fair Value Measurements (Summary Of Financial Assets And Liabilities Accounted For At Fair Value) (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Assets:
Investments in marketable securities	$ 122,505	$ 90,209
Derivatives	1,418	4,908
Total assets	123,923
Liabilities:
Derivatives	693	$ 101
Level 1 [Member]
Assets:
Investments in marketable securities	18,938
Derivatives	0
Total assets	18,938
Liabilities:
Derivatives	644
Level 2 [Member]
Assets:
Investments in marketable securities	103,567
Total assets	103,567
Liabilities:
Derivatives	0
Level 3 [Member]
Assets:
Investments in marketable securities	0
Derivatives	1,418
Total assets	1,418
Liabilities:
Derivatives	$ 49