Debt (Details) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2011
Primary revolving line of credit
Revolving line of credit
Credit facility, available credit	$ 200.0
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)	0.46%
Commitment fees payable on unused portion of the facility (as a percent)	0.08%
Other revolving credit lines
Revolving line of credit
Credit facility, available credit	$ 4.9
Credit facility, interest rate low end of range (as a percent)	2.40%
Credit facility, interest rate high end of range (as a percent)	3.70%