Stockholders' Equity (Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Feb. 27, 2015
Stockholders' Equity [Line Items]
Cash dividends declared	$ 0	$ 0	$ 0	$ 0
Value of common stock repurchased			$ 149.3	$ 129.8
Remaining shares of common stock available for purchase (in shares)	19,100,000		19,100,000
Cumulative Number Of Shares Authorized For Repurchase
Stockholders' Equity [Line Items]
Authorized stock repurchase (in shares)	90,000,000		90,000,000
Additional Authorization of Shares For Repurchase
Stockholders' Equity [Line Items]
Authorized stock repurchase (in shares)					15,000,000