Stockholders' Equity (Stock Option Activity) (Detail)	9 Months Ended
	Sep. 30, 2017 $ / shares shares
Number of options
Number of options, beginning outstanding number (in shares) | shares	8,931,000
Number of options, Granted (in shares) | shares	4,523,000
Number of options, Exercised (in shares) | shares	(11,000)
Number of options, Canceled/forfeited/expired (in shares) | shares	(2,960,000)
Number of options, ending outstanding number (in shares) | shares	10,483,174
Weighted average exercise price
Weighted average exercise price, beginning balance (in dollars per share) | $ / shares	$ 6.70
Weighted average exercise price, Granted (in dollars per share) | $ / shares	1.41
Weighted average exercise price, Exercised (in dollars per share) | $ / shares	0.38
Weighted average exercise price, Canceled/forfeited/expired (in dollars per share) | $ / shares	6.03
Weighted average exercise price, ending balance (in dollars per share) | $ / shares	$ 4.62