Stockholders' Equity (Narrative) (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended		6 Months Ended
	Jul. 31, 2015	Mar. 31, 2015	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Subsidiary, Sale of Stock [Line Items]
Common Stock, Shares Authorized			600,000,000		300,000,000
Proceeds from Issuance of Common Stock			$ 197,093	$ 107,900
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		$ 190,000
Offering costs		$ 11,600
2012 Sales Agreement [Member]
Subsidiary, Sale of Stock [Line Items]
Sales per share price range			$ 10.01
Shares sold			800,000
Proceeds from shares sold			$ 8,000
Proceeds from Issuance of Common Stock			700
2012 Sales Agreement [Member] | Subsequent Event [Member]
Subsidiary, Sale of Stock [Line Items]
Sales per share price range	$ 11.53
Shares sold	600,000
Proceeds from shares sold	$ 6,600
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			$ 50,000