Income Taxes (Summary Of Tax Loss And Tax Credit Carryforwards) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Tax Credit Carryforward [Line Items]
Deferred tax asset on tax carryforwards	$ 104,200	$ 101,300
Valuation Allowance, Amount	(123,000)	$ (148,200)
Tax Loss and Credit Carryforwards [Member]
Tax Credit Carryforward [Line Items]
Deferred tax asset on tax carryforwards	104,200
Valuation Allowance, Amount	(99,700)
Net deferred tax asset on tax carryforwards	4,500
U.S. Federal Tax Credits [Member]
Tax Credit Carryforward [Line Items]
2018-2022	0
After 2022	2,200
Indefinite	0
Total tax carryforwards	2,200
Deferred tax asset on tax carryforwards	2,200
Valuation Allowance, Amount	(1,800)
Net deferred tax asset on tax carryforwards	400
U.S Federal Tax Losses [Member]
Tax Credit Carryforward [Line Items]
2018-2022	0
After 2022	1,000
Total tax carryforwards	1,000
Deferred tax asset on tax carryforwards	200
Valuation Allowance, Amount	(200)
Net deferred tax asset on tax carryforwards	0
U.S. State Tax Credits [Member]
Tax Credit Carryforward [Line Items]
2018-2022	3,600
After 2022	1,800
Indefinite	20,600
Total tax carryforwards	26,000
Deferred tax asset on tax carryforwards	20,500
Valuation Allowance, Amount	(19,900)
Net deferred tax asset on tax carryforwards	600
U.S. State Tax Losses [Member]
Tax Credit Carryforward [Line Items]
2018-2022	43,300
After 2022	808,300
Total tax carryforwards	851,600
Deferred tax asset on tax carryforwards	45,300
Valuation Allowance, Amount	(44,600)
Net deferred tax asset on tax carryforwards	700
Non-U.S. Tax Losses [Member]
Tax Credit Carryforward [Line Items]
2018-2022	48,800
After 2022	4,500
Indefinite	132,000
Total tax carryforwards	185,300
Deferred tax asset on tax carryforwards	36,000
Valuation Allowance, Amount	(33,200)
Net deferred tax asset on tax carryforwards	$ 2,800