Fair Value Measurements (Summary Of Financial Assets And Liabilities Accounted For At Fair Value) (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Assets:
Investments in marketable securities	$ 159,822	$ 90,209
Derivatives	963	4,908
Total assets	160,785
Liabilities:
Derivatives	1,427	$ 101
Level 1
Assets:
Investments in marketable securities	57,390
Derivatives	0
Total assets	57,390
Liabilities:
Derivatives	1,434
Level 2
Assets:
Investments in marketable securities	102,432
Derivatives	302
Total assets	102,734
Liabilities:
Derivatives	30
Level 3
Assets:
Investments in marketable securities	0
Derivatives	661
Total assets	661
Liabilities:
Derivatives	$ (37)