Common Stock and Stock Warrants- Additional Information (Detail) - USD ($)	1 Months Ended	3 Months Ended
	Oct. 31, 2015	Mar. 31, 2016	Mar. 31, 2015	May. 31, 2015
Equity [Abstract]
Shelf registration, maximum common stock shares authorized				2,500,000
At-the-market sales agreement, maximum common stock shares authorized value	$ 75,000,000	$ 70,500,000		$ 75,000,000
Gross proceeds from additional follow-on public offering	34,500,000	4,500,000
Shelf registration, maximum aggregate offering price	$ 165,500,000	$ 161,000,000		$ 200.0
Class of Stock [Line Items]
Shares sold in follow-on public offering	6,272,727	499,000
Public price (in usd per share)	$ 5.50
Proceeds from issuance of common stock, net of issuance costs	$ 32,100,000	$ 4,325,000	$ 0
Underwriting discounts and commissions	2,100,000	134,000
Estimated offering expenses	$ 280,000	$ 75,000
Weighted Average [Member]
Class of Stock [Line Items]
Public price (in usd per share)		$ 8.95
Over-Allotment Option [Member]
Class of Stock [Line Items]
Shares sold in follow-on public offering	818,181