Stockholder's Equity - Shares of Common Stock Issuable on Conversion or Exercise of Rights Granted Under Prior Financing Arrangements, Stock Options and Warrants (Detail)	Dec. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total shares of common stock reserved for future issuances	15,791,860
Series E convertible voting preferred stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total shares of common stock reserved for future issuances	40,000
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total shares of common stock reserved for future issuances	10,399,265
Warrants [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total shares of common stock reserved for future issuances	395,000
Employee stock purchase plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total shares of common stock reserved for future issuances	4,611,095
Long-term retention and management incentive plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total shares of common stock reserved for future issuances	346,500