Stock-based Compensation Stock-based Compensation (Details textual) (USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2012 Years	Mar. 31, 2011
Share-based Compensation [Abstract]
Unrecognized stock-based compensation costs, net of estimated forfeitures	$ 26.2
Weighted average period of unrecognized stock-based compensation costs, net of estimated forfeitures	1.7
Cash received from the exercise of stock options	0.9	7.0
Related tax benefit realized from the exercise of the stock options	$ 0.4	$ 1.7

The weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, using a decimal to express in number of years.

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 123R

-Paragraph A240

-Subparagraph h

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (i)

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

Name:	us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition
Namespace Prefix:	us-gaap_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	duration