Stock-Based Compensation - Summary of Stock Option Activity under Plans and Related Information (Detail) - USD ($) $ / shares in Units, $ in Thousands		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014
Number of stock options outstanding
Beginning Balance		13,740,204
Granted		5,915,112
Exercised		(157,975)
Forfeited, cancelled or expired		(7,596,670)
Ending Balance		11,900,671	13,740,204
Options Vested and Exercisable, Number of Options		4,260,008
Options vested and expected to vest at end of period		10,443,746
Weighted-Average Exercise Price
Beginning Balance		$ 7.82
Granted		2.67
Exercised		1.32
Forfeited, cancelled or expired		9.62
Ending Balance		4.20	$ 7.82
Options Vested and Exercisable, Weighted Average Exercise Price (in dollars per share)		6.43
Options vested and expected to vest at end of period		$ 4.37
Weighted-Average Remaining Contractual Term
Balance at end of period		7 years 8 months 12 days	7 years 8 months 12 days
Options Vested and Exercisable, Weighted Average Remaining Contractual Term		6 years 6 months
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Weighted Average Remaining Contractual Term		7 years 8 months 12 days
Aggregate Intrinsic Value
Balance at end of period	[1]	$ 999	$ 1,680
Options vested and exercisable at end of period	[1]	945
Options vested and expected to vest at end of period	[1]	$ 989

[1] The aggregate intrinsic value represents the value by which the Company’s closing stock price on the last trading day of the year ended December 31, 2015 exceeds the exercise price of the stock multiplied by the number of options outstanding or exercisable, excluding any that have a negative intrinsic value.