Fair Value Measurements - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
8.625 % Senior Notes Due 2017
Debt Instrument [Line Items]
Long term debt, Fair Value	$ 403.1	$ 401.3
Convertible Notes Due 2017
Debt Instrument [Line Items]
Liability component of convertible note	265.9	249.6
7.5% Senior Notes due 2022
Debt Instrument [Line Items]
Liability component of convertible note	$ 324.8	$ 314.3

The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.

No definition available.

Name:	us-gaap_LongTermDebtFairValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant