Stockholders' Equity (Narrative) (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended		3 Months Ended	12 Months Ended
	Mar. 31, 2015	Jun. 30, 2014	Mar. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2012	Jan. 31, 2017	Dec. 31, 2016	Jan. 25, 2016	Jun. 18, 2015
Subsidiary, Sale of Stock [Line Items]
Sales per share price range									$ 5.56
Proceeds from shares sold				$ 204,275	$ 107,895
Common Stock, Shares Authorized				600,000,000				600,000,000
Shelf Registration Statement, Maximum Authorized Stock Issuance, Value								$ 200,000
Convertible Debt [Member]
Subsidiary, Sale of Stock [Line Items]
Adjustments to Additional Paid IN capital, Cost and Expenses on Derivative Transaction			$ 38,500
Subsequent Event [Member]
Subsidiary, Sale of Stock [Line Items]
Shelf Registration Statement, Maximum Authorized Common Stock Issuance, Value							$ 75,000
Public Offering [Member]
Subsidiary, Sale of Stock [Line Items]
Sales per share price range	$ 7.25	$ 4.00
Shares sold	27,758,620	28,750,000
Common stock issued upon exercise in full over-allotment granted	3,620,689	3,750,000
Proceeds from shares sold	$ 190,000	$ 108,000
Offering costs	$ 11,600	$ 7,100
Shelf Registration Statement, Maximum Authorized Stock Issuance, Value								$ 125,000
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				$ 14,600
Minimum [Member]
Subsidiary, Sale of Stock [Line Items]
Common Stock, Shares Authorized										300,000,000
Maximum [Member]
Subsidiary, Sale of Stock [Line Items]
Common Stock, Shares Authorized										600,000,000
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