Organization and Summary of Significant Accounting Policies - Liquidity (Detail) - USD ($) $ / shares in Units, $ in Thousands			1 Months Ended				3 Months Ended								12 Months Ended
	Jul. 23, 2015	Oct. 17, 2014	Mar. 31, 2016	Jan. 31, 2016	Feb. 28, 2015	Aug. 31, 2014	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Basis of Presentation
Accumulated deficit							$ 308,875				$ 289,852				$ 308,875	$ 289,852
Net loss							2,332	$ 5,034	$ 5,245	$ 6,412	17,288	$ 3,113	$ (1,877)	$ 3,262	19,023	21,786	$ 16,938
Cash and cash equivalents							3,887				11,400				3,887	$ 11,400	$ 21,405	$ 15,130
Proceeds from issuance of common stock and warrants, net of issuance cost					$ 10,900
Notes payable, principal							9,505								9,505
Shelf registration statement, available amount							79,000								79,000
Shelf registration statement, amount currently reserved							$ 18,200								$ 18,200
Share price, floor price required to use committed equity financing (USD per share)															$ 1.00
Share price (USD per share)							$ 0.99								$ 0.99
Remaining number of shares authorized to be repurchased (shares)							5,000,000								5,000,000
Subsequent Event
Basis of Presentation
Aggregate offering price				$ 10,000
Proceeds from issuance of common stock and warrants, net of issuance cost			$ 7,800	$ 2,200
Common Stock
Basis of Presentation
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
Common Stock | Subsequent Event
Basis of Presentation
Maximum number of warrants to be purchased (shares)				5,681,818
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
Common Stock
Basis of Presentation
Issuance of common stock (shares)					6,043,955	300,000										2,600,000
Weighted average sales price per share (USD per share)																$ 1.46
Common Stock | Subsequent Event
Basis of Presentation
Common stock, maximum number of shares to be purchased (shares)				11,363,640
Issuance of common stock (shares)				2,528,411
Loan And Security Agreement | Common Stock
Basis of Presentation
Exercise price (USD per share)		$ 1.29
Term Loan 1 | Loan And Security Agreement
Basis of Presentation
Proceeds from credit facility		$ 5,000
Notes payable, principal							$ 9,505				$ 5,000				$ 9,505	$ 5,000
Term Loan 2 | Loan And Security Agreement
Basis of Presentation
Proceeds from credit facility	$ 5,000