Common Stock - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014
Common Stock Disclosure [Line Items]
Common stock, repurchases authorized	$ 500.0
Common stock, remained available for stock repurchases	$ 500.0

Amount remaining of a stock repurchase plan authorized.

No definition available.

Name:	us-gaap_StockRepurchaseProgramRemainingAuthorizedRepurchaseAmount1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant