Warrants - Additional Information (Detail)					1 Months Ended		12 Months Ended
	Feb. 23, 2012 $ / shares shares	May. 06, 2011 $ / shares shares	Aug. 10, 2010 $ / shares $ / Stock shares	Oct. 31, 2009 $ / shares $ / Stock shares	Mar. 31, 2014 $ / shares shares	May. 31, 2010 $ / shares shares	Dec. 31, 2015 shares	Dec. 31, 2014 shares
Class of Warrant or Right [Line Items]
Common stock shares issued							19,577,729	19,404,697
Number of common shares, callable by warrants issued in the aggregate stock and warrants sale					345,661		345,661
Exercise price of warrant | $ / shares					$ 0.01
Warrant expiration date					May 31, 2019
Common stock, shares outstanding							19,577,729	19,404,697
Contractual term of the warrant					5 years
Hercules Technology Growth Capital, Inc. [Member]
Class of Warrant or Right [Line Items]
Number of common shares, callable by warrants issued in the aggregate stock and warrants sale						37,639
Exercise price of warrant | $ / shares						$ 26.90
Warrant expiration date						May 31, 2015
Contractual term of the warrant						5 years
Private Placement [Member]
Class of Warrant or Right [Line Items]
Common stock shares issued				8,107,012
Number of common shares, callable by warrants issued in the aggregate stock and warrants sale				7,296,312
Securities sold as units, description of each unit composition							Each unit consisting of one share of common stock and a warrant to purchase 0.9 shares of common stock
Number of common shares, callable by each warrants issued in the aggregate stock and warrants sale				0.9
Securities sold as units, price per unit | $ / Stock				2.4325
Exercise price of warrant | $ / shares				$ 2.77
Warrant expiration date				Oct. 31, 2016
Common stock, shares outstanding				729,627
Registered Direct Equity Issuances [Member]
Class of Warrant or Right [Line Items]
Common stock shares issued		1,192,703	668,518
Number of common shares, callable by warrants issued in the aggregate stock and warrants sale		417,445	334,258
Securities sold as units, description of each unit composition							Each unit consisting of (i) one share of common stock and (ii) a warrant to purchase 0.5 of a share of common stock
Number of common shares, callable by each warrants issued in the aggregate stock and warrants sale			0.5
Securities sold as units, price per unit | $ / Stock			27.00
Exercise price of warrant | $ / shares		$ 17.55	$ 33.00
Warrant expiration date		May 31, 2016	Aug. 31, 2015
Underwritten Public Offering [Member]
Class of Warrant or Right [Line Items]
Common stock shares issued	4,400,000
Number of common shares, callable by warrants issued in the aggregate stock and warrants sale	4,400,000
Exercise price of warrant | $ / shares	$ 5.00
Warrant expiration date	Feb. 23, 2017