Income Taxes (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Income Tax Contingency [Line Items]
Unrecognized tax benefits relating to UTPs	$ 70,000		$ 70,000
Unrecognized tax benefits, income tax penalties accrued	0		0
Unrecognized tax benefits, interest on income taxes accrued	9,200		$ 9,200
Federal statutory tax rate			21.00%		35.00%
Deferred income tax (benefit) provision	5,806	$ 14,960	$ (1,237)	$ 26,655
Potential change in unrecognized tax benefits during next twelve months	27,300		27,300
Unrecognized tax benefits that would reduce the income tax provision	46,900		46,900
Global Intangible Low-Taxed Income ("GILTI") [Member]
Income Tax Contingency [Line Items]
Deferred income tax (benefit) provision	$ (5,700)		$ (12,500)