Financial Commitments (Reconciliation Of Outstanding Debt Balance To Reported Debt Balance) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Outstanding Long-Term Debt	$ 781,907
Less: Unamortized discount and issuance costs	(45,631)	$ (56,072)
Total debt	736,276	759,519
Term Loan
Debt Instrument [Line Items]
Outstanding Long-Term Debt		57,000
Less: Unamortized discount and issuance costs		(2,350)
Total debt		54,650
Convertible Notes [Member]
Debt Instrument [Line Items]
Outstanding Long-Term Debt	200,000	200,000
Less: Unamortized discount and issuance costs	(38,365)	(47,332)
Total debt	161,635	152,668
2017 Senior Notes [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Outstanding Long-Term Debt	500,000
Less: Unamortized discount and issuance costs	(7,266)
Total debt	$ 492,734
2010 Senior Notes [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Outstanding Long-Term Debt		300,000
Less: Unamortized discount and issuance costs		(1,880)
Total debt		298,120
2014 Credit Facility [Member] | Credit Facility [Member]
Debt Instrument [Line Items]
Outstanding Long-Term Debt		152,500
Less: Unamortized discount and issuance costs		(4,510)
Total debt		$ 147,990