Stockholders' Equity (Details) (Treasury Stock, USD $) In Millions, except Share data, unless otherwise specified	0 Months Ended	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2015	Dec. 31, 2014
Treasury Stock
Equity, Class of Treasury Stock [Line Items]
Amount of shares authorized to be repurchased			$ 205.0
Shares repurchased	3,736,449	1,009,700
Cost of shares repurchased	$ 106.2	$ 31.1
Average purchase price	$ 28.41	$ 30.79