Redeemable Preferred Stock and Stockholders' Equity - Additional Information (Detail) - USD ($)					3 Months Ended				9 Months Ended		12 Months Ended
	Jun. 11, 2021	Feb. 10, 2021	Feb. 10, 2021	Jul. 23, 2020	Sep. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Temporary Equity And Stockholders Equity [Line Items]
Temporary equity preferred stock, shares authorized					1,000,000				1,000,000
Common stock, shares authorized					180,000,000		180,000,000		180,000,000		180,000,000
Common stock, shares issued		14,000,000	14,000,000		153,322,000		97,709,000		153,322,000		97,709,000
Shares Issued, Price Per Share		$ 1.03	$ 1.03
Equity raise of gross proceeds			$ 14,400,000
Series F Preferred stock, shares issued					0		1,000		0		1,000
Common stock value				$ 1,000	$ 153,000		$ 98,000		$ 153,000		$ 98,000
Proceeds from Warrant Exercise						$ 15,000,000.0
Proceeds from the exercise of common stock warrants							$ 1,500,000		$ 16,560,000	$ 46,000
Expected term (years)					6 years 1 month 6 days				6 years 1 month 6 days	5 years 6 months
Risk-free interest rate					0.98%			0.00%	0.86%	0.37%
Change in fair value of warrants									$ 0	$ (5,850,000)
Issuance costs for common stock warrants									$ 0	1,640,000
Series E Preferred stock, shares authorized					1,000,000				1,000,000
Conversion of preferred stock into common stock					251				251
Convertible preferred stock, shares outstanding					0		0		0		0
Compensation expense related to stock options					$ 200,000			$ 800,000	$ 1,500,000	2,400,000
Total unrecognized compensation expense					800,000			1,400,000	$ 800,000	1,400,000
Unrecognized share based compensation expense to be recognized over weighted-average period									1 year 6 months
Allocated Share-based Compensation Expense					$ 192,000			$ 847,000	$ 1,488,000	$ 2,367,000
Outstanding stock options, RSUs and warrants excluded from diluted loss per share									24,000,000.0	67,200,000
July 2020 Warrants
Temporary Equity And Stockholders Equity [Line Items]
Warrant issued				45,000,000
Proceeds from issuance of warrants									$ 15,300,000
Warrants issued in connection with debt instruments									$ 15,300,000
July 2020 Warrants | Rights Offering
Temporary Equity And Stockholders Equity [Line Items]
Allocated to the warrants based upon fair values				$ 15,300,000
Common Stock
Temporary Equity And Stockholders Equity [Line Items]
Other offering expenses		$ 1,100,000
Series F Convertible Preferred Stock
Temporary Equity And Stockholders Equity [Line Items]
Conversion price				$ 0.40
Series E Convertible Preferred Stock
Temporary Equity And Stockholders Equity [Line Items]
Temporary equity preferred stock, shares authorized					69,565				69,565
Series E Preferred stock, shares authorized					69,565				69,565
Convertible preferred stock, shares issued					0		0		0		0
Preferred stock par value					$ 0.001				$ 0.001
Series F Convertible Preferred Stock
Temporary Equity And Stockholders Equity [Line Items]
Temporary equity preferred stock, shares authorized					18,000				18,000
Convertible preferred stock, Common shares issued upon conversion				2,500
Series F Preferred stock, shares issued				18,000
Proceeds from issuance of warrants						2,700,000
Conversion price				$ 0.40
Proceeds of common stock and warrants				$ 18,000,000.0
Warrants issued in connection with debt instruments						$ 2,700,000
Sale of common stock, shares									18,000		17,000
Deemed dividend on convertible preferred stock				2,700,000					$ 500,000		$ 14,700,000
Series E Preferred stock, shares authorized					18,000				18,000
Preferred stock, par value					$ 0.001				$ 0.001
Convertible preferred stock, shares outstanding					251		882		251		882
Series F Convertible Preferred Stock | Rights Offering
Temporary Equity And Stockholders Equity [Line Items]
Proceeds allocated to the warrants based upon fair values				$ 2,700,000
Private Placement | Series F Convertible Preferred Stock
Temporary Equity And Stockholders Equity [Line Items]
Common stock, shares issued					627,500				627,500
Maximum
Temporary Equity And Stockholders Equity [Line Items]
Temporary equity preferred stock, shares authorized					1,000,000				1,000,000
Series E Preferred stock, shares authorized					1,000,000				1,000,000
2002 Stock Incentive Plan
Temporary Equity And Stockholders Equity [Line Items]
Common stock authorized for issuance					3,110,000				3,110,000
Options and restricted stock units outstanding					879,000				879,000
2018 Long-Term Incentive Plan
Temporary Equity And Stockholders Equity [Line Items]
Common Stock Issued Pursuant To Options Exercised									4,744,000
Increase in Number of Units Available for Issuance	24,700,000
Common stock issued pursuant to options exercised									4,744,000
2018 Long-Term Incentive Plan | Common Stock
Temporary Equity And Stockholders Equity [Line Items]
Common stock authorized for issuance					36,921,000				36,921,000
Options available for future grants					2,400,000				2,400,000
Restricted Stock Units (RSUs)
Temporary Equity And Stockholders Equity [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Granted									2,800,000
Cancelled RSU due to non achievement of performance targets									100,000
Performance-Based Awards
Temporary Equity And Stockholders Equity [Line Items]
Compensation expense related to stock options									$ 0.0		$ 900,000
Phantom Share Units (PSUs)
Temporary Equity And Stockholders Equity [Line Items]
Allocated Share-based Compensation Expense					$ 200,000				$ 200,000
Shares issued in period									10,100,000
Stock Appreciation Rights (SARs)
Temporary Equity And Stockholders Equity [Line Items]
Allocated Share-based Compensation Expense					$ 100,000				$ 200,000
Shares issued in period									700,000