Business Overview (Details) - USD ($)					1 Months Ended		3 Months Ended					6 Months Ended
	Feb. 28, 2017	Feb. 06, 2017	Jan. 31, 2017	Mar. 18, 2016	Mar. 31, 2017	Nov. 30, 2016	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Jun. 30, 2016	Mar. 31, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2015	Nov. 03, 2014
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Net cash (used in) operating activities												$ (120,772,000)	$ (60,127,000)
Cash and cash equivalents							$ 81,960,000		$ 82,387,000	$ 141,219,000		81,960,000	141,219,000	$ 61,653,000
Net loss							(73,889,000)			(38,556,000)		(138,493,000)	(98,497,000)
Income (loss) from operations							(73,583,000)			(36,860,000)		(136,310,000)	(64,410,000)
Working capital							59,400,000					59,400,000
Subsidiary, Sale of Stock [Line Items]
Proceeds of sale of common stock												121,951,000	89,845,000
Payment for indenture consent	$ 1,600,000
Debt conversion amount												4,912,000	82,274,000
Debt conversion expense							0	$ 1,209,000		$ 0		$ 1,209,000	$ 25,615,000
Common Shares
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Shares sold in private placement (in shares)												20,325,204
Subsidiary, Sale of Stock [Line Items]
Debt conversion expense (in shares)								200,000				212,800
Convertible Senior Notes Due 2019
Subsidiary, Sale of Stock [Line Items]
Debt conversion amount				$ 79,800,000	$ 4,900,000	$ 55,700,000		$ 4,911,000	$ 55,668,000		$ 79,829,000
Number of shares issued on conversion of debt (in shares)				35,300,000	1,800,000	20,500,000
Debt conversion per original conversion price (in shares)					1,600,000				2,600,000		9,600,000
Conversion price (in dollars per share)				$ 3.11											$ 3.11
Aggregate principal amount							$ 18,600,000					$ 18,600,000			$ 200,000,000
Debt conversion expense									$ 14,500,000		$ 25,600,000
Public Stock Offering
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Shares sold in private placement (in shares)			20,325,204
Shares issued (in dollars per share)			$ 6.15
Subsidiary, Sale of Stock [Line Items]
Proceeds of sale of common stock		$ 121,600,000