Consolidated Statements Of Comprehensive Income (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Consolidated Statements Of Comprehensive Income [Abstract]
Net income	$ 219.7	$ 188.0	$ 170.1
Unrealized gain on derivatives qualifying as hedges
Unrealized gain on cash flow hedge, net of tax of $(0.2) for 2010			0.3
Less: reclassification adjustment for loss on cash flow hedge included in net income, net of tax of $(0.1) and $(0.3) for 2011 and 2010, respectively		0.1	0.5
Unrealized loss on available for sale securities
Unrealized loss on securities, net of tax of $(0.1) for 2012	(0.1)
Other comprehensive income (loss)	(0.1)	0.1	0.8
Comprehensive income	$ 219.6	$ 188.1	$ 170.9