Fair Value Measurements - Additional Information (Detail) - USD ($) $ in Millions	Jun. 30, 2015	Dec. 31, 2014
1.75% Senior Notes due 2017 [Member] \| Convertible Debt [Member]
Debt Instrument [Line Items]
Fair value of Convertible Notes	$ 264.9	$ 252.6
7.5% Notes due 2022 [Member] \| Senior Notes [Member]
Debt Instrument [Line Items]
Fair value of Notes	$ 685.9	$ 664.6

Fair value portion of borrowing which can be exchanged for a specified number of another security at the option of the issuer or the holder, for example, but not limited to, the entity's common stock.

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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Convertible Security

-URI http://asc.fasb.org/extlink&oid=6509036

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