Stock Option Activity (Detail)	12 Months Ended
	Dec. 31, 2015 USD ($) $ / shares shares
Options
Outstanding at beginning of period | shares	5,817,313
Granted | shares	3,159,134
Exercised | shares	(165,805)
Forfeited | shares	(2,964,938)
Expired | shares	(1,049,699)
Outstanding at beginning of period | shares	4,796,005
Exercisable at December 31, 2015 | shares	3,153,440
Vested or expected to vest at December 31, 2015 | shares	2,276,447
Weighted-Average Exercise Price
Outstanding at beginning of period | $ / shares	$ 4.45
Granted | $ / shares	1.11
Exercised | $ / shares	1.45
Forfeited | $ / shares	1.85
Expired | $ / shares	5.27
Outstanding at beginning of period | $ / shares	3.78
Exercisable at December 31, 2015 | $ / shares	5.09
Vested or expected to vest at December 31, 2015 | $ / shares	$ 6.56
Weighted-Average Remaining Contractual Term
Outstanding at December 31, 2015	6 years 11 months 5 days
Exercisable at December 31, 2015	5 years 10 months 10 days
Vested or expected to vest at December 31, 2015	4 years 7 months 10 days
Aggregate Intrinsic Value
Outstanding at end of year | $	$ 596,660
Exercisable at end of year | $	325,107
Vested or expected to vest at end of year | $	$ 115,704