Shares of Common Stock Reserved for Issuance (Detail)	Dec. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock reserved for issuance	15,561,209
Series A Preferred Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock reserved for issuance	428,922
Series B-1 Preferred Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock reserved for issuance	961,720
Series B-2 Preferred Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock reserved for issuance	4,119,759
Exercise and conversion of Series B-2 Preferred and Series E Preferred warrants
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock reserved for issuance	72,029
Series C Preferred Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock reserved for issuance	1,949,874
Series D Preferred Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock reserved for issuance	3,196,755
Series E Preferred Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock reserved for issuance	1,672,300
Stock Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock reserved for issuance	2,129,055
Options to purchase common stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock reserved for issuance	1,030,795