Fair Value Measurements - Additional Information (Detail) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015
1 3⁄4% Senior Convertible Notes due 2017
Debt Instrument [Line Items]
Fair value disclosures	$ 258.5	$ 217.1
7 1⁄2% Senior Notes due 2022
Debt Instrument [Line Items]
Fair value of notes	$ 348.8	$ 271.3

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