Fair Value Measurements (Summary Of Financial Assets And Liabilities Accounted For At Fair Value) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Assets:
Investments in marketable securities	$ 263,497	$ 264,443
Derivatives	15,151	19,954
Total assets	278,648
Level 1 [Member]
Assets:
Investments in marketable securities	14,925
Derivatives	10,956
Total assets	25,881
Level 2 [Member]
Assets:
Investments in marketable securities	248,572
Derivatives	218
Total assets	248,790
Level 3 [Member]
Assets:
Investments in marketable securities
Derivatives	3,977
Total assets	$ 3,977