Controlled Equity Offering and Public Offering of Common Stock - Schedule of Total Sales under Sales Agreement (Detail) (Cantor Fitzgerald & Co. [Member], USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2015
Cantor Fitzgerald & Co. [Member]
Sale And Issue Of Shares Under Agreement [Line Items]
Total shares of common stock sold	733,200
Average price per share	$ 2.86
Gross proceeds	$ 2,097
Commissions earned by Cantor	63
Other issuance costs	$ 251