Convertible Preferred Stock and Warrants - Number of Shares Subject to Purchase (Detail) - USD ($) $ / shares in Units, $ in Thousands	Dec. 31, 2015	Dec. 31, 2014	Mar. 31, 2014	Feb. 12, 2014	Dec. 31, 2013	Dec. 01, 2013	Sep. 30, 2013	Sep. 03, 2013	Jun. 30, 2013	Jun. 26, 2013	Apr. 30, 2013	Mar. 31, 2013	Feb. 28, 2013	Sep. 25, 2012
Temporary Equity [Line Items]
Common Stock Value Used in Determining Fair Value (usd per share)		$ 5.93	$ 11.30	$ 7.55	$ 5.93	$ 6.77	$ 10.02	$ 9.94	$ 6.82			$ 6.85
Beneficial Conversion on Underlying Preferred Stock/ Options	$ 0	$ 0			$ 969
September 25, 2012 [Member]
Temporary Equity [Line Items]
Number of Shares Subject to Future Purchase Rights Granted														3,750,000
Fair Value per Share of Rights (usd per share)														$ 2.80
Grant Date Fair Value Recorded														$ 3,101
Common Stock Value Used in Determining Fair Value (usd per share)														$ 2.30
Beneficial Conversion on Underlying Preferred Stock/ Options														$ 0
February 28, 2013 [Member]
Temporary Equity [Line Items]
Number of Shares Subject to Future Purchase Rights Granted													891,250
Fair Value per Share of Rights (usd per share)													$ 2.83
Grant Date Fair Value Recorded													$ 864
Common Stock Value Used in Determining Fair Value (usd per share)													$ 6.85
Beneficial Conversion on Underlying Preferred Stock/ Options													$ 513
April 30, 2013 [Member]
Temporary Equity [Line Items]
Number of Shares Subject to Future Purchase Rights Granted											461,271
Fair Value per Share of Rights (usd per share)											$ 2.40
Grant Date Fair Value Recorded											$ 379
Common Stock Value Used in Determining Fair Value (usd per share)											$ 6.85
Beneficial Conversion on Underlying Preferred Stock/ Options											$ 192
June 26, 2013 [Member]
Temporary Equity [Line Items]
Number of Shares Subject to Future Purchase Rights Granted										66,250
Fair Value per Share of Rights (usd per share)										$ 0.76
Grant Date Fair Value Recorded										$ 50
Common Stock Value Used in Determining Fair Value (usd per share)										$ 6.82
Beneficial Conversion on Underlying Preferred Stock/ Options										$ 264