Options Outstanding (Detail) (USD $)	9 Months Ended
	Sep. 30, 2012	Dec. 31, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total shares issuable upon exercise	5,760,125	5,886,261
Options exercisable	3,503,567
Options not vested	2,256,558
Total shares issuable upon exercise	$ 1.11	$ 1.11
Options exercisable	$ 1.04
Options not vested	$ 1.21
Total shares issuable upon exercise	3 years 4 months 24 days
Options exercisable	3 years 3 months 18 days
Options not vested	3 years 7 months 6 days
Total shares issuable upon exercise	$ 290,332
Options exercisable	84,583
Options not vested	$ 205,749