Condensed Consolidated Statements of Stockholders' Deficit - USD ($) shares in Thousands, $ in Thousands	Total	At-the-market Offering	June 2020 Note	Facility Financing Obligation	Promissory Notes	Senior Convertible Notes	Common Stock	Common Stock At-the-market Offering	Common Stock June 2020 Note	Common Stock Facility Financing Obligation	Common Stock Promissory Notes	Common Stock Senior Convertible Notes	Additional Paid-in Capital	Additional Paid-in Capital At-the-market Offering	Additional Paid-in Capital June 2020 Note	Additional Paid-in Capital Facility Financing Obligation	Additional Paid-in Capital Promissory Notes	Additional Paid-in Capital Senior Convertible Notes	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit
Beginning Balance at Dec. 31, 2018	$ (175,082)						$ 1,870						$ 2,763,067						$ (19)	$ (2,940,000)
Beginning Balance (in shares) at Dec. 31, 2018							187,030
Net issuance of common stock associated with stock options and restricted stock units	2						$ 1						1
Net issuance of common stock associated with stock options and restricted stock units (in shares)							66
Issuance of common stock under Employee Stock Purchase Plan	317						$ 3						314
Issuance of common stock under Employee Stock Purchase Plan (in shares)							296
Stock-based compensation expense	999												999
Issuance of common stock pursuant to conversion notes						$ 538						$ 4						$ 534
Issuance of common stock pursuant to conversion notes (in shares)												386
Restricted stock unit award	105												105
Net loss	(14,883)																			(14,883)
Ending Balance at Mar. 31, 2019	(188,004)						$ 1,878						2,765,020						(19)	(2,954,883)
Ending Balance (in shares) at Mar. 31, 2019							187,778
Beginning Balance at Dec. 31, 2018	(175,082)						$ 1,870						2,763,067						(19)	(2,940,000)
Beginning Balance (in shares) at Dec. 31, 2018							187,030
Cumulative translation loss	(1)
Net loss	(37,640)
Ending Balance at Sep. 30, 2019	(184,706)						$ 2,064						2,790,890						(20)	(2,977,640)
Ending Balance (in shares) at Sep. 30, 2019							206,408
Beginning Balance at Mar. 31, 2019	(188,004)						$ 1,878						2,765,020						(19)	(2,954,883)
Beginning Balance (in shares) at Mar. 31, 2019							187,778
Net issuance of common stock associated with stock options and restricted stock units	15						$ 1						14
Net issuance of common stock associated with stock options and restricted stock units (in shares)							101
Stock-based compensation expense	2,568												2,568
Issuance of common stock		$ 1,850						$ 15						$ 1,835
Issuance of common stock (in shares)								1,568
Issuance costs associated with at-the-market offering	(41)												(41)
Net loss	(12,387)																			(12,387)
Ending Balance at Jun. 30, 2019	(195,999)						$ 1,894						2,769,396						(19)	(2,967,270)
Ending Balance (in shares) at Jun. 30, 2019							189,447
Net issuance of common stock associated with stock options and restricted stock units	31						$ 6						25
Net issuance of common stock associated with stock options and restricted stock units (in shares)							576
Issuance of common stock under Employee Stock Purchase Plan	339						$ 4						335
Issuance of common stock under Employee Stock Purchase Plan (in shares)							356
Stock-based compensation expense	1,640												1,640
Issuance of common stock pursuant to conversion notes				$ 4,575	$ 8,000	$ 5,037				$ 42	$ 71	$ 45				$ 4,533	$ 7,929	$ 4,992
Issuance of common stock pursuant to conversion notes (in shares)										4,193	7,143	4,525
Issuance of common stock		188						$ 2						186
Issuance of common stock (in shares)								168
Issuance of warrants pursuant to Credit facility	1,854												1,854
Cumulative translation loss	(1)																		(1)
Net loss	(10,370)																			(10,370)
Ending Balance at Sep. 30, 2019	(184,706)						$ 2,064						2,790,890						(20)	(2,977,640)
Ending Balance (in shares) at Sep. 30, 2019							206,408
Beginning Balance at Dec. 31, 2019	(190,526)						$ 2,118						2,799,278						(19)	(2,991,903)
Beginning Balance (in shares) at Dec. 31, 2019							211,788
Net issuance of common stock associated with stock options and restricted stock units	(317)						$ 5						(322)
Net issuance of common stock associated with stock options and restricted stock units (in shares)							504
Issuance of common stock under Employee Stock Purchase Plan	318						$ 3						315
Issuance of common stock under Employee Stock Purchase Plan (in shares)							334
Stock-based compensation expense	1,128												1,128
Issuance of common stock associated with debt interest payment	144						$ 1						143
Issuance of common stock associated with debt interest payment (in shares)							99
Issuance of common stock		522						$ 4						518
Issuance of common stock (in shares)								413
Issuance costs associated with at-the-market offering	(16)												(16)
Write-off of cumulative translation loss	19																		19
Net loss	(9,322)																			(9,322)
Ending Balance at Mar. 31, 2020	(198,050)						$ 2,131						2,801,044							(3,001,225)
Ending Balance (in shares) at Mar. 31, 2020							213,138
Beginning Balance at Dec. 31, 2019	(190,526)						$ 2,118						2,799,278						$ (19)	(2,991,903)
Beginning Balance (in shares) at Dec. 31, 2019							211,788
Cumulative translation loss	(19)
Net loss	(30,829)
Ending Balance at Sep. 30, 2020	(186,420)						$ 2,309						2,834,003							(3,022,732)
Ending Balance (in shares) at Sep. 30, 2020							230,923
Beginning Balance at Mar. 31, 2020	(198,050)						$ 2,131						2,801,044							(3,001,225)
Beginning Balance (in shares) at Mar. 31, 2020							213,138
Net issuance of common stock associated with stock options and restricted stock units	117						$ 3						114
Net issuance of common stock associated with stock options and restricted stock units (in shares)							297
Stock-based compensation expense	2,185												2,185
Issuance of common stock from the exercise of warrants	11,600						$ 73						11,527
Issuance of common stock from the exercise of warrants (in Share)							7,250
Issuance of common stock pursuant to conversion notes			$ 2,630						$ 12						$ 2,618
Issuance of common stock pursuant to conversion notes (in shares)									1,235
Issuance of common stock		12,366						$ 75						12,291
Issuance of common stock (in shares)								7,459
Issuance costs associated with at-the-market offering	(320)												(320)
Issuance of common stock from market price stock purchase	14												14
Issuance of common stock under Market Price Stock Purchase Plan (in shares)							10
Adjustment of common stock in association with restricted stock units							$ (5)						5
Adjustment of common stock in association with restricted stock units (in shares)							(461)
Net loss	(10,252)																			(10,252)
Ending Balance at Jun. 30, 2020	(179,710)						$ 2,289						2,829,478							(3,011,477)
Ending Balance (in shares) at Jun. 30, 2020							228,928
Net issuance of common stock associated with stock options and restricted stock units	101						$ 1						100
Net issuance of common stock associated with stock options and restricted stock units (in shares)							82
Issuance of common stock under Employee Stock Purchase Plan	366						$ 3						363
Issuance of common stock under Employee Stock Purchase Plan (in shares)							293
Stock-based compensation expense	1,294												1,294
Issuance of common stock associated with debt interest payment	144						$ 1						143
Issuance of common stock associated with debt interest payment (in shares)							89
Issuance of common stock		$ 2,679						$ 15						$ 2,664
Issuance of common stock (in shares)								1,531
Issuance costs associated with at-the-market offering	(39)												(39)
Net loss	(11,255)																			(11,255)
Ending Balance at Sep. 30, 2020	$ (186,420)						$ 2,309						$ 2,834,003							$ (3,022,732)
Ending Balance (in shares) at Sep. 30, 2020							230,923