Stockholders' Equity (Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended	9 Months Ended
	Mar. 31, 2015	Sep. 30, 2015	Dec. 31, 2014
Subsidiary, Sale of Stock [Line Items]
Common Stock, Shares Authorized		600,000,000	300,000,000
Public Offering [Member]
Subsidiary, Sale of Stock [Line Items]
Sales per share price range	$ 7.25
Shares sold	27,758,620
Common stock issued upon exercise in full over-allotment granted	3,620,689
Proceeds from shares sold	$ 190.0
Offering costs	$ 11.6
2012 Sales Agreement [Member]
Subsidiary, Sale of Stock [Line Items]
Sales per share price range		$ 10.63
Shares sold		1,400,000
Proceeds from shares sold		$ 14.6
Maximum [Member] | 2012 Sales Agreement [Member]
Subsidiary, Sale of Stock [Line Items]
Common stock authorized for issuance under prior shelf registration statement with SEC, dollar amount		$ 50.0