Consolidated Statements of Convertible Preferred Stock, Redeemable Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($)	Total	Common Stock	Additional Paid-In-Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit	Series B-2 Convertible Preferred Stock	Series B Convertible Preferred Stock	Series A-1 Convertible Preferred Stock	Series A-2 Convertible Preferred Stock	Series A-3 Convertible Preferred Stock	Series A-4 Convertible Preferred Stock	Series A-5 Convertible Preferred Stock	Series A-6 Convertible Preferred Stock
Stock issued during period, shares, new issue						448,060							186,847
Stock issued during period, value, new issue						$ 26,152,000							$ 10,109,000
Balance at Dec. 31, 2013	$ (277,301,000)	$ 0	$ 0	$ 0	$ (277,301,000)						$ 271,000
Balance (in shares) at Dec. 31, 2013		385,664					701,235	939,612		142,227	3,998	6,443	496,111
Increase (Decrease) in Stockholders' Equity
Net loss	(62,479,000)				(62,479,000)
Unrealized gain (loss) from available-for-sale securities	(21,000)			(21,000)
Accretion of dividends on preferred stock	(9,000,000)		(4,542,000)		(4,458,000)	$ (685,000)		$ (3,084,000)
Issuance of warrants	41,000		41,000
Exercise of warrants (in shares)		20,435
Stock options exercised (in shares)		49,382
Stock options exercised	170,000		170,000
Share-based compensation expense	7,070,000		7,070,000
Issuance of common stock, net (in shares)		10,141,268
Issuance of common stock, net	103,804,000	$ 1,000	103,803,000
Conversion of convertible preferred stock into common stock (in shares)		22,327,786				(448,060)	(701,235)	(939,612)	(983,208)	(142,227)	(3,998)	(6,443)	(682,958)
Conversion of convertible preferred stock into common stock	298,063,000	$ 2,000	298,061,000			$ (26,837,000)	$ (45,407,000)	$ (81,821,000)	$ (97,223,000)	$ (12,702,000)	$ (271,000)	$ (525,000)	$ (33,277,000)
Reclassification of warrant liability to additional paid in capital	3,117,000		3,117,000
Balance at Dec. 31, 2014	63,464,000	$ 3,000	407,720,000	(21,000)	(344,238,000)	0				$ 0		$ 0	$ 0
Balance (in shares) at Dec. 31, 2014		32,924,535					0			0	0	0	0
Increase (Decrease) in Stockholders' Equity
Net loss	(101,526,000)				(101,526,000)
Unrealized gain (loss) from available-for-sale securities	26,000			26,000
Accretion of dividends on preferred stock	0
Exercise of warrants (in shares)		529,862
Stock options exercised (in shares)		267,684
Stock options exercised	2,337,000		2,337,000
Share-based compensation expense	14,734,000		14,734,000
Issuance of common stock, net (in shares)		9,262,162
Issuance of common stock, net	482,250,000	$ 1,000	482,249,000
Balance at Dec. 31, 2015	461,285,000	$ 4,000	907,040,000	5,000	(445,764,000)	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0
Balance (in shares) at Dec. 31, 2015		42,984,243				0	0	0	0	0	0	0	0
Increase (Decrease) in Stockholders' Equity
Net loss	(182,804,000)				(182,804,000)
Unrealized gain (loss) from available-for-sale securities	66,000			66,000
Accretion of dividends on preferred stock	0
Exercise of warrants (in shares)		19,172
Stock options exercised (in shares)		137,719
Stock options exercised	2,573,000		2,573,000
Share-based compensation expense	26,058,000		26,058,000
Issuance of common stock, net	0
Balance at Dec. 31, 2016	$ 307,178,000	$ 4,000	$ 935,671,000	$ 71,000	$ (628,568,000)	$ 0		$ 0		$ 0		$ 0	$ 0
Balance (in shares) at Dec. 31, 2016		43,141,134.000				0	0			0	0	0	0