Financial Commitments (Reconciliation Of Outstanding Debt Balance To Reported Debt Balance) (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Unamortized Discounts and Issuance Costs	$ (57,434)	$ (56,072)
Total debt	862,660	759,519
2017 Credit Facility [Member]
Debt Instrument [Line Items]
Outstanding Long-Term Debt	125,000
Unamortized Discounts and Issuance Costs	(6,840)
Total debt	118,160
2014 Credit Facility [Member]
Debt Instrument [Line Items]
Outstanding Long-Term Debt		152,500
Unamortized Discounts and Issuance Costs		(4,510)
Total debt		147,990
2017 Senior Notes [Member]
Debt Instrument [Line Items]
Outstanding Long-Term Debt	500,000
Unamortized Discounts and Issuance Costs	(7,640)
Total debt	492,360
2010 Senior Notes [Member]
Debt Instrument [Line Items]
Outstanding Long-Term Debt		300,000
Unamortized Discounts and Issuance Costs		(1,880)
Total debt		298,120
Term Loan [Member]
Debt Instrument [Line Items]
Outstanding Long-Term Debt		57,000
Unamortized Discounts and Issuance Costs		(2,350)
Total debt		54,650
Convertible Notes [Member]
Debt Instrument [Line Items]
Outstanding Long-Term Debt	200,000	200,000
Unamortized Discounts and Issuance Costs	(42,954)	(47,332)
Total debt	$ 157,046	$ 152,668