Financial Commitments (Reconciliation Of Outstanding Debt Balance To Reported Debt Balance) (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Unamortized Discount and Issuance Costs	$ (43,064)	$ (45,631)
Total debt	817,284	736,276
Convertible Notes [Member]
Debt Instrument [Line Items]
Outstanding Long-Term Debt	200,000	200,000
Unamortized Discount and Issuance Costs	(35,990)	(38,365)
Total debt	164,010	161,635
2017 Senior Notes [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Outstanding Long-Term Debt	500,000	500,000
Unamortized Discount and Issuance Costs	(7,074)	(7,266)
Total debt	$ 492,926	$ 492,734