Subsequent Event (Details) (Repurchase of common shares, USD $) In Millions, unless otherwise specified	1 Months Ended
Jul. 31, 2012	Jul. 30, 2012 year
Repurchase of common shares
Subsequent Event
Common stock repurchase program, amount authorized	$ 500.0
Common stock repurchase program, period (in years)		2

The number of years over which shares may be purchased under a stock repurchase plan authorized by an entity's Board of Directors.

No definition available.

Name:	us-gaap_StockRepurchaseProgramPeriodInForce
Namespace Prefix:	us-gaap_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	instant