Common Stock - Schedule of Shares Reserved for Future Issuance (Detail) - shares shares in Thousands	Jun. 30, 2015	Dec. 31, 2014
Options To Purchase Common Stock [Member]
Class of Stock [Line Items]
Shares reserved for future issuance	19,426	19,567
Common Stock Warrants [Member]
Class of Stock [Line Items]
Shares reserved for future issuance	377	2,381
Conversion Premium On Notes [Member]
Class of Stock [Line Items]
Shares reserved for future issuance	25,000	25,000