Stockholders' Equity - Additional Information (Detail) - USD ($)		1 Months Ended				12 Months Ended
	Jul. 23, 2015	Mar. 31, 2016	Jan. 31, 2016	Feb. 28, 2015	Aug. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Oct. 17, 2014
Stockholders Equity Note
Preferred stock, shares authorized (shares)						10,000,000	10,000,000
Preferred stock, par value (USD per share)						$ 0.001	$ 0.001
Preferred stock shares outstanding (shares)						0	0
Proceeds from issuance of common stock and warrants, net of issuance cost				$ 10,900,000
Stock and warrant issuance costs				100,000
Proceeds from issuance of common stock						$ 10,869,000	$ 5,913,000	$ 16,612,000
Share price, floor price required to use committed equity financing (USD per share)						$ 1.00
Remaining number of shares authorized to be repurchased (shares)						5,000,000
Share price (USD per share)						$ 0.99
Number of securities called by warrants (shares)						8,837,351			480,392
Warrant liability				$ 5,100,000		$ 1,841,000	0
Common Stock
Stockholders Equity Note
Warrant exercise price (USD per share)				$ 1.82	$ 1.97
Class of warrant number of securities called by each warrant (shares)				0.5
Warrants, period from issuance in which warrants are exercisable				6 months 1 day
Warrant expiration period				7 years
Warrants issued (in shares)				3,021,977
February 2022
Stockholders Equity Note
Warrant exercise price (USD per share)				$ 1.82		$ 1.82
Number of securities called by warrants (shares)				3,021,977		3,021,977
July 2025
Stockholders Equity Note
Warrant exercise price (USD per share)	$ 1.64					$ 1.64
Warrant expiration period	10 years
Number of securities called by warrants (shares)	152,440					152,440
Aspire Capital Common Stock Purchase Agreement
Stockholders Equity Note
Proceeds from issuance of common stock							$ 3,700,000
At The Market Equity Offering
Stockholders Equity Note
Issuance of common stock (shares)							954,922	312,450
Proceeds from issuance of common stock							$ 2,200,000	$ 800,000
Subsequent Event
Stockholders Equity Note
Aggregate offering price			$ 10,000,000
Proceeds from issuance of common stock and warrants, net of issuance cost		$ 7,800,000	$ 2,200,000
Subsequent Event | Common Stock
Stockholders Equity Note
Maximum number of warrants to be purchased (shares)			5,681,818
Warrant exercise price (USD per share)			$ 0.88
Class of warrant number of securities called by each warrant (shares)			0.5
Warrants, period from issuance in which warrants are exercisable			6 months 1 day
Warrant expiration period			7 years
Warrants issued (in shares)			1,264,204
Series A Junior Participating Preferred Stock
Stockholders Equity Note
Preferred stock, shares authorized (shares)						1,000,000.0
Series B 8% Cumulative Convertible Preferred Stock
Stockholders Equity Note
Preferred stock, shares authorized (shares)						800
Preferred stock dividend rate						8.00%
Series C 6% Cumulative Convertible Preferred Stock
Stockholders Equity Note
Preferred stock, shares authorized (shares)						600
Preferred stock dividend rate						6.00%
Series D Junior Participating Cumulative Preferred Stock
Stockholders Equity Note
Preferred stock, shares authorized (shares)						50,000
Common Stock
Stockholders Equity Note
Issuance of common stock (shares)				6,043,955	300,000		2,600,000
Common share purchase agreement, shares authorized					$ 22,000,000.0
Common stock purchase agreement, term					24 months
Common stock purchase agreement, commitment fee, amount					$ 400,000
Weighted average sales price per share (USD per share)							$ 1.46
Common stock, shares authorized, remaining amount						$ 18,200,000.0
Common Stock | Subsequent Event
Stockholders Equity Note
Common stock, maximum number of shares to be purchased (shares)			11,363,640
Issuance of common stock (shares)			2,528,411