Stock-Based Compensation Stock-Based Compensation - Summary of Restricted Stock and Stock Units Grants (Details) (Restricted stock units and stock grants, USD $)	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Restricted stock units and stock grants
Stocks granted and the weighted average fair value
Units granted (in shares)	130,273	129,620	202,278
Grant date fair value (in dollars per share)	$ 54.91	$ 55.21	$ 49.31

The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)(2)(iii)(1)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

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Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration