Summary Information about Options Outstanding (Detail) (USD $)	3 Months Ended
	Mar. 31, 2014
Share Based Compensation Shares Authorized Under Stock Option Plans Exercise Price Range [Line Items]
Range of Exercise Prices, lower limit	$ 0.52
Range of Exercise Prices, upper limit	$ 6.95
Options Number Outstanding	7,842,917
Options Outstanding Weighted Average Remaining Contractual Life (Years)	7 years 5 months 27 days
Options Outstanding Weighted Average Exercise Price	$ 1.28
Options Number Exercisable	3,110,282
Options Exercisable Weighted Average Exercise Price	$ 1.94
Range 1
Share Based Compensation Shares Authorized Under Stock Option Plans Exercise Price Range [Line Items]
Range of Exercise Prices, lower limit	$ 0.52
Range of Exercise Prices, upper limit	$ 0.80
Options Number Outstanding	1,877,646
Options Outstanding Weighted Average Remaining Contractual Life (Years)	9 years 1 month 10 days
Options Outstanding Weighted Average Exercise Price	$ 0.65
Options Number Exercisable	198,584
Options Exercisable Weighted Average Exercise Price	$ 0.71
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	$ 0.84
Options Number Outstanding	90,000
Options Outstanding Weighted Average Remaining Contractual Life (Years)	9 years 2 months 9 days
Options Outstanding Weighted Average Exercise Price	$ 0.84
Options Number Exercisable	66,667
Options Exercisable Weighted Average Exercise Price	$ 0.84
Range 3
Share Based Compensation Shares Authorized Under Stock Option Plans Exercise Price Range [Line Items]
Range of Exercise Prices, lower limit	$ 0.85
Range of Exercise Prices, upper limit	$ 0.88
Options Number Outstanding	2,665,000
Options Outstanding Weighted Average Remaining Contractual Life (Years)	9 years 11 months 12 days
Options Outstanding Weighted Average Exercise Price	$ 0.88
Options Number Exercisable	833
Options Exercisable Weighted Average Exercise Price	$ 0.88
Range 4
Share Based Compensation Shares Authorized Under Stock Option Plans Exercise Price Range [Line Items]
Range of Exercise Prices, lower limit	$ 0.89
Range of Exercise Prices, upper limit	$ 1.44
Options Number Outstanding	1,622,836
Options Outstanding Weighted Average Remaining Contractual Life (Years)	5 years 11 months 5 days
Options Outstanding Weighted Average Exercise Price	$ 1.22
Options Number Exercisable	1,308,172
Options Exercisable Weighted Average Exercise Price	$ 1.19
Range 5
Share Based Compensation Shares Authorized Under Stock Option Plans Exercise Price Range [Line Items]
Range of Exercise Prices, lower limit	$ 1.45
Range of Exercise Prices, upper limit	$ 6.95
Options Number Outstanding	1,587,435
Options Outstanding Weighted Average Remaining Contractual Life (Years)	2 years 11 months 9 days
Options Outstanding Weighted Average Exercise Price	$ 2.76
Options Number Exercisable	1,536,026
Options Exercisable Weighted Average Exercise Price	$ 2.78