Common Stock Repurchases - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	6 Months Ended	12 Months Ended
Jun. 30, 2013	Dec. 31, 2012
Equity [Abstract]
Value of shares remaining under stock repurchase program	$ 356.3
Maximum amount authorized under stock repurchase program		$ 500.0
Date the Company's board of directors authorized stock repurchase programs		August 1, 2012

Amount remaining of a stock repurchase plan authorized by an entity's Board of Directors.

No definition available.

Name:	us-gaap_StockRepurchaseProgramRemainingAuthorizedRepurchaseAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration