Subsequent Events (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2012
New Credit Agreement [Member]
Subsequent Event [Line Items]
Date entered into New Credit Agreement	Apr. 27, 2012
Expiration date of credit facility	April 2017
New committed credit facility	$ 300.0
New Credit Agreement accordion feature, maximum borrowing	350.0
New Credit Agreement amount available for swing-line loans	30.0
New Credit Agreement amount available for issuance of letters of credit	30.0
Line of credit interest rate, margin added to LIBOR, at minimum (in hundredths)	1.25%
Line of credit interest rate, margin added to LIBOR, at maximum (in hundredths)	2.25%
Revolving Credit Facility [Member]
Subsequent Event [Line Items]
Prior revolving credit facility	$ 225.0
Expiration date of credit facility	June 2014