Debt (Details) (USD $) In Millions	3 Months Ended
	Jun. 30, 2011	Mar. 31, 2011
Debt [Abstract]
Credit facility, maximum borrowing capacity	$ 200	$ 150
Credit facility, expiration date	November 1, 2012
Credit facility, permitted increase in maximum borrowing capacity	100	150
Amount borrowed under the amended credit facility	129.5
Restriction on maximum additional borrowing outside amended credit facility	$ 250