Description of Business and Basis of Preparation - Additional Information (Detail) - USD ($)				6 Months Ended
	Jun. 21, 2016	Apr. 10, 2016	Nov. 16, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015	Jul. 31, 2006
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Formation date				Nov. 04, 1999
Number of warrants issued to purchase common stock (in shares)				14,033		14,033
Payment of stock issuance costs				$ 1,746,000	$ 3,335,000
Sales Agreement Prospectus [Member]
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Stock issued				$ 558,000
June 2016 Public Offering
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Stock issued (in shares)	9,375,000
Number of warrants issued to purchase common stock (in shares)	4,218,750
Price per share (in dollars per share)	$ 2.40
Exercise price of warrants (in dollars per share)	$ 3.00
Stock issued	$ 20,754,000
Payment of stock issuance costs	$ 1,746,000
Common Stock [Member]
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Shelf registration maximum equity offering price			$ 150,000,000
Number of warrants issued to purchase common stock (in shares)							14,033
Exercise price of warrants (in dollars per share)							$ 45.61
Common Stock [Member] | Sales Agreement Prospectus [Member]
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Shelf registration maximum equity offering price		$ 40,000,000	$ 40,000,000