Stock Repurchases (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended	12 Months Ended		3 Months Ended
	Mar. 31, 2014	Dec. 31, 2013	Mar. 07, 2013	Mar. 31, 2013 Open Market [Member]	Mar. 31, 2014 Tender Offer [Member]		Mar. 31, 2014 Other [Member]		Mar. 31, 2013 Other [Member]
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
Common stock repurchased, shares	775,296	537,054		530,795	637,420	[1]	137,876	[2]	6,259	[2]
Common stock repurchased, value	$ 103.6	$ 59.7		$ 59.0	$ 85.2	[1]	$ 18.4	[2]	$ 0.7	[2]
Tender offer, offering costs	$ 0.2

[1] Tender Offer Cost amounts include offering costs of $0.2 million.

[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.