Stockholders' Equity (Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Feb. 27, 2015
Stockholders' Equity [Line Items]
Cash dividends declared	$ 0	$ 0	$ 0	$ 0
Value of common stock repurchased			$ 91.6	$ 72.0
Remaining shares of common stock available for purchase (in shares)	20,800,000		20,800,000
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