Stock-Based Compensation - Summary of the Reserved Shares of Common Stock for Future Issuance (Detail) - shares	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total shares reserved	5,400,264	3,674,726
1997 Stock Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total shares reserved	4,712,576	2,835,151
2001 Stock Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total shares reserved	50,530	68,810
Employee Stock Purchase Plan ("ESPP") [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total shares reserved	637,158	770,765