Equity Incentive Plans and Stock Based Compensation - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of shares issued and outstanding	5.00%
Increase in authorized shares	1,250,000
Aggregate intrinsic value of options outstanding	$ 10,500,000
Aggregate intrinsic value of options exercisable	8,600,000
Options vested and expected to vest	6,483,107
Aggregate intrinsic value of options vested and expected to vest	10,500,000
Weighted average remaining contractual life of options vested and expected to vest	7 years 6 months 18 days
Weighted average exercise price of options vested and expected to vest	$ 3.65
Intrinsic value of stock options exercised	500,000	1,700,000	6,000
Cash received from stock option exercises	100,000	600,000	14,000
Tax benefit realized upon exercise of option	0	0	0
Offering period	24 months
Purchase period	6 months
Common stock purchased by employees	167,245	150,677
Common stock purchased under Purchase Plan at average price	$ 1.69	$ 1.18
Amount withheld by plan participants to purchase stock	300,000
Discount available to eligible employees related to employee stock purchase plan	85.00%
Shares authorized and available for issuance under the ESPP	235,896
Stock-based compensation expense	4,922,000	3,010,000	1,039,000
Non-employees stock-based compensation expense	100,000	200,000	100,000
2004 Equity Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of fair market value	100.00%
Terms of stock options granted	10 years
Terms of stock options vested	4 years
Employee Stock-based Compensation Expense [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	4,800,000	2,800,000	800,000
Unrecognized compensation cost related to unvested stock-based awards granted to employees under the stock option plans	$ 10,300,000
Unrecognized compensation cost related to unvested stock-based awards granted to employees under the stock option plans, period for recognition	2 years 4 months 24 days