Debt (Details) (USD $) In Millions, unless otherwise specified		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2012 Primary revolving line of credit	Jun. 30, 2012 Other revolving credit lines and long term debt	Jul. 27, 2012 Unsecured credit agreement
Debt
Credit facility, maximum borrowing capacity	$ 206.3	$ 200.0
Total Borrowing Capacity			10.8
Credit facility, interest rate basis		LIBOR
Credit facility, interest rate spread (as a percent)		0.27%
Credit facility, interest rate at end of period (as a percent)		0.52%
Commitment fees payable on unused portion of the facility (as a percent)		0.08%
Credit facility, interest rate low end of range (as a percent)			1.50%
Credit facility, interest rate high end of range (as a percent)			7.25%
Total outstanding balances			4.8
Revolving credit facility current borrowing capacity				300.0
Borrowing capacity of the terminated line of credit facility				$ 200.0