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Debt Obligations (Changes in Debt Obligations Additional Information) (Details) (USD $)
In Millions, unless otherwise specified |
3 Months Ended | 12 Months Ended | 3 Months Ended | 1 Months Ended | |||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
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Mar. 31, 2013
2.50% convertible senior notes due August 15, 2013 [Member]
item
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Mar. 31, 2008
2.50% convertible senior notes due August 15, 2013 [Member]
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Dec. 31, 2012
2.50% convertible senior notes due August 15, 2013 [Member]
item
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Mar. 31, 2012
2.50% convertible senior notes due August 15, 2013 [Member]
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Mar. 31, 2013
4.00% senior unsecured notes due January 15, 2015 [Member]
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Mar. 31, 2013
5.55% senior unsecured notes due January 15, 2020 [Member]
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Mar. 31, 2013
5.25% senior unsecured notes due January 16, 2018 [Member]
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Mar. 31, 2013
$450 million senior unsecured term loan facility credit agreement due September 19, 2016 [Member]
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Mar. 31, 2013
$750 million revolving credit commitment due September 19, 2016 [Member]
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Sep. 30, 2011
2011 Credit Facility [Member]
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Mar. 31, 2013
2011 Credit Facility [Member]
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| Debt Conversion [Line Items] | |||||||||||
| Debt instrument, interest rate | 2.50% | 2.50% | 2.50% | 4.00% | 5.55% | 5.25% | |||||
| Debt instrument, maturity date | Aug. 15, 2013 | Aug. 15, 2013 | Jan. 15, 2015 | Jan. 15, 2020 | Jan. 16, 2018 | Sep. 19, 2016 | Sep. 19, 2016 | Sep. 19, 2016 | |||
| Debt instrument, principal outstanding | $ 475.0 | $ 450.0 | |||||||||
| Debt instrument convertible, number of equity instruments | 1,722,508 | 1,715,517 | |||||||||
| Debt Instrument, interest rate during period | 1.58% | 1.38% | |||||||||
| Credit facility, borrowing capacity | $ 750 | $ 1,200 | $ 1,200 | ||||||||