Stockholders' Equity (Stock Option Activity) (Detail)	6 Months Ended
	Jun. 30, 2017 $ / shares shares
Number of options
Number of options, outstanding at December 31, 2016 (in shares) | shares	8,931,000
Number of options, Granted (in shares) | shares	4,255,000
Number of options, Exercised (in shares) | shares	(8,000)
Number of options, Canceled/forfeited/expired (in shares) | shares	(2,359,000)
Number of options, outstanding at March 31, 2017 (in shares) | shares	10,819,036
Weighted average exercise price
Weighted average exercise price, Options outstanding at December 31, 2016 (in dollars per share) | $ / shares	$ 6.70
Weighted average exercise price, Granted (in dollars per share) | $ / shares	1.44
Weighted average exercise price, Exercised (in dollars per share) | $ / shares	0.38
Weighted average exercise price, Canceled/forfeited/expired (in dollars per share) | $ / shares	5.86
Weighted average exercise price, Options outstanding at March 31, 2017 (in dollars per share) | $ / shares	$ 4.82