Financing Arrangements (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010	Apr. 30, 2011
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 200.0		$ 200.0		$ 125.0
Revolving credit facility, amount outstanding	0	0	0	0
Expiration date of revolving credit facility			June 2013
Annual commitment fee on undrawn amounts of revolving credit facility			0.375%
Line of Credit Facility, Commitment Fee Percentage, Rate Spread Over Bank Base Rate			0.50%
Line of Credit Facility, Commitment Fee Percentage, Rate Spread Over LIBOR			1.50%
Line of Credit Facility, Commitment Fee Amount	$ 0.2	$ 0.1	$ 0.3	$ 0.2