Summary Information about Options Outstanding (Detail) (USD $)	9 Months Ended
	Sep. 30, 2013
Share Based Compensation Shares Authorized Under Stock Option Plans Exercise Price Range [Line Items]
Range of Exercise Prices, lower limit	$ 0.72
Range of Exercise Prices, upper limit	$ 8.34
Options Number Outstanding	4,769,621
Options Outstanding Weighted Average Remaining Contractual Life (Years)	6 years 8 months 1 day
Options Outstanding Weighted Average Exercise Price	$ 1.67
Options Number Exercisable	2,982,413
Options Exercisable Weighted Average Exercise Price	$ 2.02
Range 1
Share Based Compensation Shares Authorized Under Stock Option Plans Exercise Price Range [Line Items]
Range of Exercise Prices, lower limit	$ 0.72
Range of Exercise Prices, upper limit	$ 0.80
Options Number Outstanding	1,181,979
Options Outstanding Weighted Average Remaining Contractual Life (Years)	9 years 3 months 29 days
Options Outstanding Weighted Average Exercise Price	$ 0.77
Options Number Exercisable	150,604
Options Exercisable Weighted Average Exercise Price	$ 0.72
Range 2
Share Based Compensation Shares Authorized Under Stock Option Plans Exercise Price Range [Line Items]
Range of Exercise Prices, lower limit	$ 0.81
Range of Exercise Prices, upper limit	$ 1.20
Options Number Outstanding	1,289,169
Options Outstanding Weighted Average Remaining Contractual Life (Years)	7 years 5 months 19 days
Options Outstanding Weighted Average Exercise Price	$ 1.14
Options Number Exercisable	1,177,461
Options Exercisable Weighted Average Exercise Price	$ 1.15
Range 3
Share Based Compensation Shares Authorized Under Stock Option Plans Exercise Price Range [Line Items]
Range of Exercise Prices, lower limit	$ 1.21
Range of Exercise Prices, upper limit	$ 2.40
Options Number Outstanding	1,068,405
Options Outstanding Weighted Average Remaining Contractual Life (Years)	5 years 8 months 16 days
Options Outstanding Weighted Average Exercise Price	$ 1.80
Options Number Exercisable	505,295
Options Exercisable Weighted Average Exercise Price	$ 2.19
Range 4
Share Based Compensation Shares Authorized Under Stock Option Plans Exercise Price Range [Line Items]
Range of Exercise Prices, lower limit	$ 2.41
Range of Exercise Prices, upper limit	$ 3.13
Options Number Outstanding	956,113
Options Outstanding Weighted Average Remaining Contractual Life (Years)	4 years 4 months 10 days
Options Outstanding Weighted Average Exercise Price	$ 2.69
Options Number Exercisable	875,098
Options Exercisable Weighted Average Exercise Price	$ 2.71
Range 5
Share Based Compensation Shares Authorized Under Stock Option Plans Exercise Price Range [Line Items]
Range of Exercise Prices, lower limit	$ 3.14
Range of Exercise Prices, upper limit	$ 8.34
Options Number Outstanding	273,955
Options Outstanding Weighted Average Remaining Contractual Life (Years)	3 years 1 month 24 days
Options Outstanding Weighted Average Exercise Price	$ 3.95
Options Number Exercisable	273,955
Options Exercisable Weighted Average Exercise Price	$ 3.95