Income Taxes (Reconciliation of Provision for Income Taxes) (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Federal statutory income tax rate, percent		35.00%	35.00%	35.00%
Expected tax expense at U.S. Federal statutory rate of 35%		$ 169,860	$ 91,179	$ 49,658
State income taxes, net of Federal income tax effect		6,404	7,261	4,783
Foreign earnings at other than U.S. rates		(87,514)	14,639	5,310
Federal and California R&D tax credits		(79,868)	(41,144)	(29,363)
Excess tax benefits on stock-based compensation		(157,888)	0	0
Tax Cuts and Jobs Act of 2017		79,077	0	0
Release of tax reserves on previously unrecognized tax benefits		0	0	(13,438)
Other		(3,679)	1,894	2,294
Provision for income taxes	$ 79,100	$ (73,608)	$ 73,829	$ 19,244
Effective Tax Rate		(15.00%)	28.00%	14.00%