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Stock-Based Compensation Expense - Summary of Stock Option Activity (Detail) - $ / shares
3 Months Ended 12 Months Ended
Mar. 31, 2016
Dec. 31, 2015
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]    
Number of Options, Outstanding, Beginning Balance 2,369,847  
Number of Options, Granted 945,480  
Number of Options, Canceled (31,000)  
Number of Options, Outstanding, Ending Balance 3,284,327 2,369,847
Number of Options, Vested and expected to vest 3,183,159  
Number of Options, Vested and exercisable 1,260,974  
Weighted Average Exercise Price Per Share, Outstanding, Beginning Balance $ 13.99  
Weighted Average Exercise Price Per Share, Granted 7.91  
Weighted Average Exercise Price Per Share, Canceled 13.46  
Weighted Average Exercise Price Per Share, Outstanding, Ending Balance 12.23 $ 13.99
Weighted Average Exercise Price Per Share, Vested and expected to vest 12.31  
Weighted Average Exercise Price Per Share, Vested and Exercisable $ 16.35  
Weighted Average Contractual Term, Outstanding 8 years 6 months 7 days 8 years 3 months 11 days
Weighted Average Contractual Term, Vested and Expected to Vest 8 years 2 months 27 days  
Weighted Average Contractual Term, Vested and Exercisable 7 years 4 months 21 days  
Weighted-average grant date fair value of Stock Options Outstanding, Granted $ 5.88