Fair Value Measurements (Summary Of Financial Assets And Liabilities Accounted For At Fair Value) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Assets:
Investments in equity securities	$ 7,936
Derivatives	37,750	24,129
Total assets	45,686
Liabilities:
Derivatives	9,100	7,828
Level 1 [Member]
Assets:
Investments in equity securities	7,936
Derivatives	20,177
Total assets	28,113
Level 2 [Member]
Assets:
Derivatives	2,068
Total assets	2,068
Liabilities:
Derivatives	6,836
Level 3 [Member]
Assets:
Derivatives	15,505
Total assets	15,505
Liabilities:
Derivatives	$ 2,264