Financial Commitments (Reconciliation of Outstanding Debt Balance to Reported Debt Balance) (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Unamortized Discount and Issuance Costs	$ (26,358)	$ (34,998)
Total debt	836,244	761,504
Convertible Notes [Member]
Debt Instrument [Line Items]
Outstanding Long-Term Debt	200,000	200,000
Unamortized Discount and Issuance Costs	(20,506)	(28,519)
Total debt	179,494	171,481
2017 Senior Notes [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Outstanding Long-Term Debt	500,000	500,000
Unamortized Discount and Issuance Costs	(5,852)	(6,479)
Total debt	$ 494,148	$ 493,521