Income Taxes (Summary Of Tax Loss And Tax Credit Carryforwards) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Tax Credit Carryforward [Line Items]
Deferred tax asset on tax carryforwards	$ 124,800	$ 104,200
Valuation Allowance, Amount	(124,300)	$ (123,000)
Tax Loss and Credit Carryforwards [Member]
Tax Credit Carryforward [Line Items]
Deferred tax asset on tax carryforwards	124,700
Valuation Allowance, Amount	(101,200)
Net deferred tax asset on tax carryforwards	23,500
U.S. Federal Tax Credits [Member]
Tax Credit Carryforward [Line Items]
2019-2023	2,800
After 2023	1,000
Indefinite	800
Total tax carryforwards	4,600
Deferred tax asset on tax carryforwards	4,600
Valuation Allowance, Amount	(2,900)
Net deferred tax asset on tax carryforwards	1,700
U.S Federal Tax Losses [Member]
Tax Credit Carryforward [Line Items]
2019-2023	0
After 2023	900
Indefinite	27,300
Total tax carryforwards	28,200
Deferred tax asset on tax carryforwards	5,900
Valuation Allowance, Amount	(200)
Net deferred tax asset on tax carryforwards	5,700
U.S. State Tax Credits [Member]
Tax Credit Carryforward [Line Items]
2019-2023	2,600
After 2023	4,200
Indefinite	22,100
Total tax carryforwards	28,900
Deferred tax asset on tax carryforwards	22,900
Valuation Allowance, Amount	(20,200)
Net deferred tax asset on tax carryforwards	2,700
U.S. State Tax Losses [Member]
Tax Credit Carryforward [Line Items]
2019-2023	56,500
After 2023	815,000
Indefinite	2,100
Total tax carryforwards	873,600
Deferred tax asset on tax carryforwards	45,800
Valuation Allowance, Amount	(45,100)
Net deferred tax asset on tax carryforwards	700
Non-U.S. Tax Losses [Member]
Tax Credit Carryforward [Line Items]
2019-2023	45,600
After 2023	4,400
Indefinite	181,100
Total tax carryforwards	231,100
Deferred tax asset on tax carryforwards	45,500
Valuation Allowance, Amount	(32,800)
Net deferred tax asset on tax carryforwards	$ 12,700