Stockholder's Equity (Deficit) and Stock-Based Compensation - Additional Information (Detail) (USD $)	1 Months Ended	3 Months Ended		9 Months Ended
	May 31, 2013	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Stockholders Equity Note [Line Items]
Common stock, shares issued	8,901,675	110,347,285		110,347,285		98,798,065
Common stock, per share	$ 2.30	$ 0.01		$ 0.01		$ 0.01
Convertible preferred stock, shares issued	41,418
Convertible preferred stock, per share	$ 230	$ 0.01		$ 0.01		$ 0.01
Common stock issuable on conversion of preferred stock	100
Percentage equity ownership by holder, together with affiliates	9.99%
Proceed from offering	$ 29,100,000			$ 29,068,000
Compensation expense		1,524,000	748,000	4,353,000	2,776,000
Stock-based compensation expense related to modification of certain stock options				4,353,000	2,775,000
1995 Equity Incentive Plan (the Equity Plan)
Stockholders Equity Note [Line Items]
Number of shares available for future grants		4,119,641		4,119,641
Compensation expense		1,410,000	733,000	4,188,000	2,744,000
Employee Stock Purchase Plans
Stockholders Equity Note [Line Items]
Percentage of price per share				85.00%
Employee stock purchase plan offering period				6 months
Contribution of employee in percentage				10.00%
Contribution of employee in shares		875		875
Compensation expense		114,000	15,000	165,000	32,000
Number of shares purchased in period				45,001	48,748
Number of shares reserved and available for issuance		317,938		317,938
Stock Options | 1995 Equity Incentive Plan (the Equity Plan)
Stockholders Equity Note [Line Items]
Vesting period				48 months
Contractual life of option				10 years
Restricted Stock | 1995 Equity Incentive Plan (the Equity Plan)
Stockholders Equity Note [Line Items]
Vesting period				4 years
Stock Compensation Plan
Stockholders Equity Note [Line Items]
Stock based compensation capitalized into inventory		1,000	9,000	8,000	15,000
Stock-based compensation expense related to modification of certain stock options		$ 385,000	$ 46,000	$ 1,600,000	$ 428,000