CONSOLIDATED STATEMENTS OF CONVERTIBLE REDEEMABLE PREFERRED STOCK AND SHAREHOLDERS’ EQUITY (DEFICIT) - USD ($) $ in Thousands	Series A convertible redeemable preferred stock	Series B convertible redeemable preferred stock	Series C convertible redeemable preferred stock	Series D convertible redeemable preferred stock	Common Stock	Additional Paid-In Capital	Treasury Stock, at cost	Accumulated Deficit	Total
Balance at beginning of year at Dec. 31, 2013	$ 12,277	$ 49,376	$ 12,154		$ 1	$ 12,313	$ (3)	$ (80,536)
Balance at beginning of year at Dec. 31, 2013									$ (68,225)
Balance at beginning of year (in shares) at Dec. 31, 2013					962,960
Increase (decrease) in convertible redeemable preferred stock
Exercise of common stock options						72			72
Exercise of common stock options, shares					32,390
Issuance of restricted stock awards to employees, shares					10,869
Accruals of dividends and accretion to redemption value	504	1,836	960						3,300
Accruals of dividends and accretion to redemption value								(3,300)	(3,300)
Stock-based compensation expense						22			22
Net loss								(17,917)	(17,917)
Balance at end of year at Dec. 31, 2014	$ 12,781	$ 51,212	$ 13,114		$ 1	12,407	(3)	(101,753)
Balance at end of year at Dec. 31, 2014									(89,348)
Balance at end of year (in shares) at Dec. 31, 2014	9,232,334	27,324,237	8,658,008		1,006,219
Increase (decrease) in convertible redeemable preferred stock
Exercise of common stock options						517			517
Exercise of common stock options, shares					173,251
Issuance of restricted stock awards to employees, shares					194,694
Accruals of dividends and accretion to redemption value	$ 2,297	$ 18,034	$ 2,996	$ 1,245					24,572
Accruals of dividends and accretion to redemption value						(24,572)			(24,572)
Exercise of warrants						6			6
Exercise of warrants (in shares)					16,062
Issuance of convertible redeemable preferred stock, net of issuance costs				$ 44,807
Issuance of convertible redeemable preferred stock, net of issuance costs, shares				37,500,000
Conversion of notes to convertible redeemable preferred stock				$ 5,000
Conversion of notes to convertible redeemable preferred stock, shares				4,166,667
Extinguishment of prior preferred stock dividends	(3,733)	(23,341)	(4,110)
Extinguishment of prior preferred stock dividends						31,184			31,184
Conversion of preferred stock to common stock	$ (11,345)	$ (45,905)	$ (12,000)	$ (50,000)	$ 13	119,237			119,250
Conversion of preferred stock to common stock, shares	9,232,334	27,324,237	8,658,008	41,666,667	12,591,463
Public offering of common stock, net of issuance costs					$ 7	72,022			72,029
Public offering of common stock, net of issuance costs, shares					6,670,000
Issuance of common stock in payment of accrued dividends				$ (1,052)		1,052			1,052
Issuance of common stock in payment of accrued dividends, shares					87,662
Stock-based compensation expense						2,209			2,209
Net loss								(27,255)	(27,255)
Balance at end of year at Dec. 31, 2015					$ 21	214,062	(3)	(129,008)
Balance at end of year at Dec. 31, 2015									85,072
Balance at end of year (in shares) at Dec. 31, 2015					20,739,351
Increase (decrease) in convertible redeemable preferred stock
Exercise of common stock options						443			443
Exercise of common stock options, shares					81,831
Public offering of common stock, net of issuance costs					$ 8	137,332			137,340
Public offering of common stock, net of issuance costs, shares					8,500,000
Issuance for employee stock purchase plan						442			442
Issuance for employee stock purchase plan, shares					42,918
Retirement of treasury stock						(3)	$ 3
Stock-based compensation expense						5,787			5,787
Net loss								(94,176)	(94,176)
Balance at end of year at Dec. 31, 2016					$ 29	$ 358,063		$ (223,184)
Balance at end of year at Dec. 31, 2016									$ 134,908
Balance at end of year (in shares) at Dec. 31, 2016					29,364,100