Stockholders' Equity (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013
Share repurchase program
Cumulative shares that have been repurchased in stock repurchase program	26.3
Cumulative value of shares repurchased in stock repurchase program	$ 428.9
Remaining shares authorized to be repurchased	5.2

The remaining number of shares authorized to be repurchased by an entity's Board of Directors under a stock repurchase plan.

No definition available.

Name:	us-gaap_StockRepurchaseProgramRemainingNumberOfSharesAuthorizedToBeRepurchased
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant