Income Taxes Schedule of Effective Income Tax Rate Reconciliation (Details)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Tax at federal statutory rate	35.00%	35.00%	35.00%
State, net of federal benefit	1.10%	1.80%	2.60%
Impact of international operations	(6.40%)	(2.70%)	7.10%
Stock-based compensation	(0.90%)	1.20%	(0.40%)
Tax credits	(1.60%)	(0.90%)	(1.20%)
Impact of the Tax Act	53.30%	0.00%	0.00%
Others	(1.90%)	(0.30%)	0.10%
Effective Income Tax Rate Reconciliation, Percent	78.60%	34.10%	43.20%