Fair Value Measurements (Summary Of Financial Assets And Liabilities Accounted For At Fair Value) (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Assets:
Investments in marketable securities	$ 200,513	$ 201,910
Derivatives	7,189	$ 9,052
Total assets	207,702
Liabilities:
Derivatives	0
Level 1 [Member]
Assets:
Investments in marketable securities	48,792
Derivatives	4,487
Total assets	53,279
Liabilities:
Derivatives	0
Level 2 [Member]
Assets:
Investments in marketable securities	151,721
Total assets	151,721
Liabilities:
Derivatives	0
Level 3 [Member]
Assets:
Investments in marketable securities	0
Derivatives	2,702
Total assets	2,702
Liabilities:
Derivatives	$ 0