Net Income Per Common Share Earnings Per Share (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended
Jun. 30, 2012
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	3.125%
Maximum Number Of Shares To Be Purchased By Company Under Call Option	19.8
Price Per Share Of Common Stock To Be Purchased By Company Under Call Option	$ 30.29
2.625% Senior Convertible Debentures [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	2.625%

Interest rate stated in the contractual debt agreement.

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 22

-Article 5

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 210.5-02.22(a)(1))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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