Accretion of Debt Discount Included or Expected to be Included in Condensed Consolidated Financial Statements (Detail) (USD $) In Millions	6 Months Ended
	Jun. 30, 2011
3.25% Cash Convertible Senior Notes due 2014 | Remainder of 2011
Debt Instrument [Line Items]
Amount of the accretion of debt discount expected	$ 12.0
3.25% Cash Convertible Senior Notes due 2014 | 2012
Debt Instrument [Line Items]
Amount of the accretion of debt discount expected	26.0
3.25% Cash Convertible Senior Notes due 2014 | 2013
Debt Instrument [Line Items]
Amount of the accretion of debt discount expected	28.8
3.25% Cash Convertible Senior Notes due 2014 | 2014
Debt Instrument [Line Items]
Amount of the accretion of debt discount expected	12.9
1.00% Senior Convertible Debentures due 2027 | Remainder of 2011
Debt Instrument [Line Items]
Amount of the accretion of debt discount expected	1.5	[1]
1.00% Senior Convertible Debentures due 2027 | 2012
Debt Instrument [Line Items]
Amount of the accretion of debt discount expected	$ 0.3	[1]

[1] At our option, the Debentures are subject to redemption at any time on or after February 1, 2012, in whole or in part, at a redemption price equal to 100% of the principal amount of the Debentures being redeemed, plus accrued and unpaid interest. In addition, holders may require us to repurchase their Debentures on February 1, 2012, February 1, 2017, and February 1, 2022, in whole or in part, for cash at a repurchase price equal to 100% of the principal amount of the Debentures being repurchased, plus accrued and unpaid interest. For purposes of this chart, we have assumed that the Debentures will be repurchased pursuant to the holders' option on February 1, 2012.