Stockholders' Equity - Additional Information (Detail)			1 Months Ended				12 Months Ended
	Jan. 01, 2019 shares	Jan. 02, 2018 shares	Jul. 31, 2019 USD ($) $ / shares shares	Jan. 31, 2019 USD ($) $ / shares shares	Jun. 30, 2018 USD ($) Arithmeticaverage Day $ / shares shares	Nov. 30, 2017 USD ($)	Dec. 31, 2019 USD ($) PurchasePeriod $ / shares shares	Dec. 31, 2018 USD ($) $ / shares shares	Feb. 27, 2020 shares	Dec. 31, 2017 USD ($)	Apr. 30, 2013
Stockholders Equity [Line Items]
Shares of common stock issued							111,393,000	37,474,000
Preferred stock, shares issued							20,000	18,000
Preferred stock, shares authorized							10,000,000	10,000,000
Preferred stock, shares outstanding							19,714	17,697
Common stock, voting rights							One vote per share
Proceeds from issuance of common stock through controlled equity offering facilities, net | $							$ 32,022,000
Options granted, Number of Shares							1,716,000
Shares Available for Future Grant							1,422,000
Share of common stock value | $										$ 25,000
Number of shares issued under employee stock purchase plan							133,322	104,099
Subsequent Event [Member]
Stockholders Equity [Line Items]
Number of warrants, expired									10,245
2011 Plan [Member]
Stockholders Equity [Line Items]
Common stock available for issuance automatic increase period							10 years
Common stock available for issuance automatic increase maximum number of shares							4.00%
Shares of common stock available for issuance	1,498,960	1,371,308
Options granted, Number of Shares							1,715,518
Shares Available for Future Grant							1,154,817
Stock Option Plans [Member]
Stockholders Equity [Line Items]
Shares Available for Future Grant							1,155,000
Stock Option Plans [Member] | New Employees [Member]
Stockholders Equity [Line Items]
Option exercisable on first anniversary of vesting commencement date, percent							25.00%
Portion of option exercisable for each month over vesting percent							2.083%
Stock option plans, vesting period							4 years
Vesting rights							New employees, of which 25% of the shares subject to such options become exercisable on the first anniversary of the vesting commencement date, and 1/48th of the shares subject to such options become exercisable each month over the remainder of the four-year vesting period
Stock Option Plans [Member] | Existing Employees [Member]
Stockholders Equity [Line Items]
Vesting rights							Existing employees with various vesting schedules over three to four years
Stock Option Plans [Member] | New Non-Employee Board Members [Member]
Stockholders Equity [Line Items]
Portion of option exercisable for each month over vesting percent							4.166%
Stock option plans, vesting period							2 years
Vesting rights							New non-employee members of the board of directors, of which 50% of the shares subject to such options become exercisable on each of the first and second anniversary of the vesting commencement date
Stock Option Plans [Member] | Continuing Non-Employee Board Members [Member]
Stockholders Equity [Line Items]
Portion of option exercisable for each month over vesting percent							8332.00%
Stock option plans, vesting period							1 year
Vesting rights							Continuing non-employee members of the board of directors, of which 1/24th of the shares subject to such options become exercisable each month following the date of grant over a two-year vesting period
Maximum [Member] | Stock Option Plans [Member] | Existing Employees [Member]
Stockholders Equity [Line Items]
Stock option plans, vesting period							4 years
Minimum [Member] | Stock Option Plans [Member] | Existing Employees [Member]
Stockholders Equity [Line Items]
Stock option plans, vesting period							3 years
Series F Convertible Preferred Stock [Member]
Stockholders Equity [Line Items]
Price per common share | $ / shares							$ 600
Shares issued upon conversion							1,000
Preferred stock, shares outstanding							8,333
Series E Convertible Preferred Stock [Member]
Stockholders Equity [Line Items]
Price per common share | $ / shares							$ 500
Shares issued upon conversion							1,000
Preferred stock, shares outstanding							10,000
Numbers of shares converted							7,000
Series D Convertible Preferred Stock [Member]
Stockholders Equity [Line Items]
Price per common share | $ / shares							$ 2,000
Shares issued upon conversion							1,000
Preferred stock, shares outstanding							1,381
Numbers of shares converted							1,119
Series D, Series E and Series F Convertible Preferred Stock [Member]
Stockholders Equity [Line Items]
Preferred stock, payment to stock holders in the event of liquidation, dissolution or winding up preference per share | $ / shares							$ 0.0001
Preferred stock, voting rights							Shares of Series D, Series E, and Series F Stock will generally have no voting rights, except as required by law and except that the consent of holders of a majority of the outstanding Series D and Series E Stock will be required to amend the terms of the Series D, Series E, and Series F Stock.
Series D, Series E and Series F Convertible Preferred Stock [Member] | Maximum [Member]
Stockholders Equity [Line Items]
Percentage of outstanding common stock							9.98%
Series B Convertible Preferred Stock [Member]
Stockholders Equity [Line Items]
Preferred stock, shares outstanding							0
Numbers of shares converted							13,639
Series C Convertible Preferred Stock [Member]
Stockholders Equity [Line Items]
Preferred stock, shares outstanding							0
Numbers of shares converted							1,558
Common Stock [Member]
Stockholders Equity [Line Items]
Common stock, shares issued upon conversion of convertible preferred stock							11,950,165
Number of shares issued under employee stock purchase plan							134,000	104,000
Underwritten Public Offering [Member]
Stockholders Equity [Line Items]
Shares of common stock issued			38,333,717	23,000,000
Proceeds from issuance of common and convertible preferred stock, gross | $			$ 28,000,000	$ 20,000,000
Proceeds from issuance of common and convertible preferred stock, net | $			$ 26,100,000	$ 18,500,000
Underwritten Public Offering [Member] | Series F Convertible Preferred Stock [Member]
Stockholders Equity [Line Items]
Preferred stock, shares issued			8,333
Shares issued upon conversion			1,000
Underwritten Public Offering [Member] | Series F Convertible Preferred Stock [Member] | Maximum [Member]
Stockholders Equity [Line Items]
Percentage of outstanding common stock			9.98%
Underwritten Public Offering [Member] | Series E Convertible Preferred Stock [Member]
Stockholders Equity [Line Items]
Preferred stock, shares issued				17,000
Shares issued upon conversion				1,000
Underwritten Public Offering [Member] | Series E Convertible Preferred Stock [Member] | Maximum [Member]
Stockholders Equity [Line Items]
Percentage of outstanding common stock				9.98%
Underwritten Public Offering [Member] | Common Stock [Member]
Stockholders Equity [Line Items]
Price per common share | $ / shares			$ 0.60	$ 0.50
Underwritten Public Offering [Member] | Preferred Stock [Member] | Series F Convertible Preferred Stock [Member]
Stockholders Equity [Line Items]
Price per common share | $ / shares			$ 600.00
Underwritten Public Offering [Member] | Preferred Stock [Member] | Series E Convertible Preferred Stock [Member]
Stockholders Equity [Line Items]
Price per common share | $ / shares				$ 500.00
Over-Allotment Option [Member]
Stockholders Equity [Line Items]
Shares of common stock issued			5,000,050
Controlled Equity Offering Facilities [Member]
Stockholders Equity [Line Items]
Common stock sales agreement, date							2011-08
Proceeds from issuance of common shares, gross | $							$ 500,000	$ 1,400,000
Proceeds from issuance of common stock through controlled equity offering facilities, net | $							500,000	$ 1,400,000
Issuance of common stock, remaining offering value | $							$ 43,100,000
Controlled Equity Offering Facilities [Member] | Common Stock [Member]
Stockholders Equity [Line Items]
Price per common share | $ / shares							$ 1.19	$ 2.38
Common stock, shares sold							400,000	600,000
Additional Controlled Equity Offerings Facilities [Member]
Stockholders Equity [Line Items]
Issuance of common stock, commission percentage, maximum						3.00%					3.00%
Common stock sales agreement further amended, date							2017-11
Increase in aggregate controlled equity offering agreement as per amendment | $						$ 45,000,000
CSPA [Member] | Aspire [Member]
Stockholders Equity [Line Items]
Proceeds from issuance of common stock through controlled equity offering facilities, net | $					$ 500,000
Common stock purchase agreement period					24 months
Average lowest closing sales price | Arithmeticaverage					3
Consecutive business days | Day					10
Percentage of volume weighted average price					97.00%
Request to purchase shares per business day					2,000,000
Number of shares of common stock issued as commitment fee					212,329
Commitment fee | $					$ 400,000
Other transaction costs | $					100,000
CSPA [Member] | Aspire [Member] | Registration Rights Agreement [Member]
Stockholders Equity [Line Items]
Price per common share | $ / shares								$ 2.20
Common stock, shares sold							0	2,390,640
Proceeds from issuance of common stock through controlled equity offering facilities, net | $								$ 4,600,000
Remaining purchase commitment | $							$ 10,900,000
CSPA [Member] | Maximum [Member] | Aspire [Member]
Stockholders Equity [Line Items]
Issuance of common stock, offering value | $					15,500,000
Commitment to purchase additional common shares | $					$ 15,000,000
Percentage of additional trading volume of shares					30.00%
CSPA [Member] | Minimum [Member] | Aspire [Member]
Stockholders Equity [Line Items]
Closing price of common stock | $ / shares					$ 0.25
CSPA [Member] | Common Stock [Member] | Aspire [Member]
Stockholders Equity [Line Items]
Price per common share | $ / shares					$ 2.19
Common stock, shares sold					228,311
CSPA [Member] | Common Stock [Member] | Maximum [Member] | Aspire [Member]
Stockholders Equity [Line Items]
Shares of common stock to purchase per business day					200,000
Employee Stock Purchase Plan [Member]
Stockholders Equity [Line Items]
Common stock available for issuance automatic increase period							10 years
Common stock available for issuance automatic increase maximum number of shares							1.00%
Shares of common stock available for issuance	336,000
Shares Available for Future Grant							266,983
Purchase price of a share as a percentage of fair market value							85.00%
Duration of offering period							12 months
Number of purchase periods in each offering period | PurchasePeriod							2
Duration of each purchase period							6 months