Income Taxes Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2018	Mar. 31, 2017
Income Tax Disclosure [Abstract]
Effective Income Tax Rate Reconciliation, Percent	21.00%	35.00%
Excess tax benefits associated with stock-based compensation	$ 0.7	$ 0.8

Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from share-based compensation.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32632-109319

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 25
-Paragraph 20
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=96869850&loc=d3e28680-109314

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32621-109319

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant