Common Stock - Additional Information (Detail) - USD ($)		3 Months Ended	9 Months Ended
	Jul. 13, 2015	Sep. 30, 2015	Sep. 30, 2015	Dec. 31, 2014	Sep. 30, 2014
Class of Stock [Line Items]
Common stock, shares authorized		200,000,000	200,000,000	200,000,000
Common stock, par value		$ 0.01	$ 0.01	$ 0.01
Common stock, shares issued		115,101,000	115,101,000	106,697,000
Common stock, shares outstanding		115,101,000	115,101,000	106,697,000
Net proceeds from issuance of common stock after deducting commissions and offering expenses			$ 38,560,000
Cowen and Company Llc [Member] | At the Market Offering [Member]
Class of Stock [Line Items]
Common stock, shares issued		3,800,000	3,800,000
Net proceeds from issuance of common stock after deducting commissions and offering expenses		$ 38,600,000
Maximum [Member] | Cowen and Company Llc [Member] | At the Market Offering [Member]
Class of Stock [Line Items]
Aggregate sales price of offering	$ 40,000,000
Common Stock Warrants [Member]
Class of Stock [Line Items]
Number of warrants cash or cashless exercised		2,100,000	2,100,000		400,000
Weighted average exercise price of warrants		$ 3.00	$ 3.00		$ 3.40
Number of common stock issued as a result of cash and cashless exercise of warrants		1,500,000	1,500,000		300,000