Debt (Details) (USD $) In Millions, unless otherwise specified	1 Months Ended
	Oct. 31, 2011 New Credit Agreement [Member]	Oct. 05, 2011 New Credit Agreement [Member]	Oct. 04, 2011 Prior Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Credit agreement, maximum borrowing capacity		$ 800.0	$ 400.0
Term of credit agreement (in years)		5 Y
Amount available for stand-by letters of credit		$ 150.0
Credit agreement, expiration date	2016-10-04
Annual facility fee (in basis points)		22.5
Credit spread (in basis points)		127.5
Maximum leverage ratio		3.5
Minimum fixed charge coverage ratio		1.5