Stock Repurchases (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended			6 Months Ended
	Jun. 30, 2014		Jun. 30, 2013	Jun. 30, 2014		Jun. 30, 2013		Mar. 07, 2013
Equity, Class of Treasury Stock [Line Items]
Increase in number of shares authorized for repurchase								1,000,000
Remaining number of shares authorized for repurchase	324,456			324,456
Common stock repurchased, shares	915,750		326,629	1,691,046		863,683
Common stock repurchased, value	$ 115.1		$ 36.2	$ 218.7		$ 95.9
Open Market [Member]
Equity, Class of Treasury Stock [Line Items]
Common stock repurchased, shares	0		326,629	0		857,424
Common stock repurchased, value	0		36.2	0		95.2
Tender Offer [Member]
Equity, Class of Treasury Stock [Line Items]
Common stock repurchased, shares	915,750		0	1,553,170		0
Common stock repurchased, value	115.1	[1]	0	200.3	[1]	0
Tender offer, offering costs	0.1			0.3
Other [Member]
Equity, Class of Treasury Stock [Line Items]
Common stock repurchased, shares				137,876	[2]	6,259	[2]
Common stock repurchased, value				$ 18.4	[2]	$ 0.7	[2]

[1] Tender Offer Cost amounts include offering costs of $0.1 million and $0.3 million for the three and six months ended June 30, 2014, respectively.

[2] Represents shares of common stock released to us as payment of tax withholdings due to us upon the vesting of restricted stock and restricted stock units.