Stockholders' Equity Share Repurchase and Retirement (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2017	Sep. 30, 2017	Jun. 10, 2016
Class of Stock [Line Items]
Stock Repurchased and Retired During Period, Value	$ 47.9	$ 58.0
Stock Repurchase Program, Authorized Amount			$ 150.0
Stock Repurchased During Period, Shares	999,618	1,228,449
Additional Paid-in Capital [Member]
Class of Stock [Line Items]
Stock Repurchased and Retired During Period, Value	$ 10.8	$ 13.2
Retained Earnings [Member]
Class of Stock [Line Items]
Stock Repurchased and Retired During Period, Value	$ 37.1	$ 44.8

Equity impact of the value of stock that has been repurchased and retired during the period. The excess of the purchase price over par value can be charged against retained earnings (once the excess is fully allocated to additional paid in capital).

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=84159872&loc=d3e21463-112644

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(28))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(29))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration