Income Taxes (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating Loss Carryforwards [Line Items]
Provisional income tax charge for re-measurement of deferred tax assets and liabilities	$ 64,800
Income tax charge to establish valuation allowance related to R&D credits	48,600
Tax benefit due to recognition of income tax effects related to stock based compensation	22,000
Provisional income tax charge for transition tax on repatriation of deferred foreign income	364,600
Valuation allowance	(76,789)	$ (14,156)
Tax benefit from release of uncertain tax positions due to expiration of statute of limitations	8,764	1,167
Decrease in unrecognized tax benefits for closed tax years			$ 20,300
Unrecognized tax benefits	77,849	$ 69,801	$ 54,621
Accrued interest and penalties	2,700
Research
Operating Loss Carryforwards [Line Items]
Tax credit carryforward	108,600
United States
Operating Loss Carryforwards [Line Items]
Net operating loss carry forwards	135,900
Foreign jurisdictions
Operating Loss Carryforwards [Line Items]
Net operating loss carry forwards	47,200
Long-term Deferred Tax Assets
Operating Loss Carryforwards [Line Items]
Unrecognized tax benefits	$ 31,600