Equity Incentive Plans - Additional Information (Detail) - USD ($)	1 Months Ended		12 Months Ended
	Apr. 30, 2015	May. 31, 2013	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2005
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares, Exercisable			912,785
Options to exercise, shares			1,196,172
2005 Equity Incentive Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Authorized for issuance thereunder share of common stock						108,879
Effective date of Equity Incentive Plan 2005 and closing date of company's initial public offering						Mar. 08, 2006
Vesting period for stock options and restricted stock units						4 years
Maximum contractual term for issuing new grants stock options and restricted stock units						10 years
Increase in annual reserve by percentage of shares of common stock						2.00%
Increase in annual reserve by shares of common stock						100,000
Shares authorized for issuance include annual reserve					119,812
Shares available for issuance					1,667,850
2005 Equity Incentive Plan [Member] | Restricted Stock Units [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Restricted stock units granted to non-employee directors			1 year
2005 Non-Employee Director's Stock Option Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Authorized for issuance thereunder share of common stock						25,000
Vesting period for stock options and restricted stock units						4 years
Maximum contractual term for issuing new grants stock options and restricted stock units						10 years
Authorized shares of common stock for issuance, Number of Shares		200,000
Shares authorized for issuance include annual reserve				2,200,000
Shares available for issuance				136,110
2015 Equity Incentive Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period for stock options and restricted stock units	4 years
Maximum contractual term for issuing new grants stock options and restricted stock units	10 years
Authorized shares of common stock for issuance, Number of Shares	1,000,000
Shares available for issuance			2,503,057
2015 Non Employee Directors' Stock Option Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period for stock options and restricted stock units	1 year
Maximum contractual term for issuing new grants stock options and restricted stock units	10 years
Authorized shares of common stock for issuance, Number of Shares	250,000
Number of shares, Exercisable			912,785
Weighted average exercise price exercisable			$ 8.16
Intrinsic value of options exercised			$ 0	$ 26,000	$ 13,000
Options to exercise, shares			5,610
Common stock price, per share			$ 0.70
Shares available for issuance			400,000
2011 Employee Stock Option Exchange Program [Member] | Restricted Stock Units [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total value of options exercised restricted stock units			$ 28,000	$ 136,000	$ 75,000
2005 Plan and the Directors’ Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares authorized for issuance include annual reserve			175,000
2015 Plan and the 2015 Directors’ Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Authorized shares of common stock for issuance, Number of Shares			1,250,000
Shares authorized for issuance include annual reserve			1,250,000
2005 Employee Stock Purchase Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Authorized for issuance thereunder share of common stock						50,000
Increase in annual reserve by percentage of shares of common stock			1.00%
Authorized shares of common stock for issuance, Number of Shares			75,000
Employee stock purchase plan fixed offering period historically						24 months
Employees purchase common stock on their enrollment date			85.00%
Employee stock purchase plan current offering period			6 months
2015 Employee Stock Purchase Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Authorized shares of common stock for issuance, Number of Shares	500,000
Shares available for issuance			26,157	70,226	54,494
Employees purchase common stock on their enrollment date	85.00%
Shares that were not purchased by our employees			128,249
Shares issued under ESPP			75,000	75,000	75,000
Weighted average price			$ 1.46	$ 2.82	$ 3.67
Shares available for issuance under the ESPP			628,249