Warrant Liability - Additional Information (Detail)	1 Months Ended			6 Months Ended	12 Months Ended
	Apr. 30, 2015 USD ($) $ / shares shares	Dec. 31, 2011 $ / shares shares	Nov. 30, 2009 USD ($) $ / shares $ / Institutions shares	Jun. 30, 2015 shares	Dec. 31, 2014 USD ($) shares	Dec. 31, 2013 USD ($) shares	Dec. 31, 2012 USD ($) shares	Dec. 31, 2011 USD ($) $ / shares $ / Stock_Unit shares
Class of Warrant or Right [Line Items]
Exercise price of warrants | $ / shares	$ 0.85
Proceeds from issuance of common stock and warrants | $	$ 25,000,000
Number of shares issued upon warrants exercise	35,715,000
Series A Warrants [Member]
Class of Warrant or Right [Line Items]
Proceeds from sale of stock | $					$ 1,652,000	$ 538,000	$ 3,078,000
Common Stock [Member]
Class of Warrant or Right [Line Items]
Number of securities callable by each warrant or right warrants	0.75
November 2009 Financing [Member]
Class of Warrant or Right [Line Items]
Number of units sold to investors			1,000,000
Price per unit | $ / shares			$ 12.50
Gross proceeds from units sold to investors | $			$ 12,500,000
Proceeds from sale of stock | $			$ 11,985,000
November 2009 Financing [Member] | Common Stock [Member]
Class of Warrant or Right [Line Items]
Number of securities callable by each warrant or right warrants			0.40
Exercise price of warrants | $ / shares			$ 15.00
Number of securities callable by warrants			400,000
Number of warrants in each unit sold to institutional investors | $ / Institutions			1
Warrant expiration				November 2009
December 2011 Financing [Member]
Class of Warrant or Right [Line Items]
Price per unit | $ / shares								$ 1.25
Proceeds from issuance of common stock and warrants | $								$ 10,000,000
Number of Series A warrants in each unit issued in public offering | $ / Stock_Unit								1
December 2011 Financing [Member] | Series A Warrants [Member]
Class of Warrant or Right [Line Items]
Number of securities callable by warrants		8,000,000						8,000,000
Number of warrants exercised					1,180,015	384,534	2,198,571
Number of shares issued upon warrants exercise							2,700,000
December 2011 Financing [Member] | Series B Warrant [Member]
Class of Warrant or Right [Line Items]
Number of securities callable by warrants		8,000,000						8,000,000
Warrant expiration				2012-May-02
Term of warrant								90 days
Number of warrants exercised							2,700,000
Number of warrants expired				5,300,000
December 2011 Financing [Member] | Series A Warrants [Member]
Class of Warrant or Right [Line Items]
Number of securities callable by warrants		8,000,000						8,000,000
Term of warrant		5 years
December 2011 Financing [Member] | Common Stock [Member]
Class of Warrant or Right [Line Items]
Number of shares issued upon warrants exercise							2,700,000
Number of shares issued upon warrants exercise					1,180,015	384,534	2,198,571
December 2011 Financing [Member] | Common Stock [Member] | Series A Warrants [Member]
Class of Warrant or Right [Line Items]
Exercise price of warrants | $ / shares		$ 1.40						$ 1.40
December 2011 Financing [Member] | Common Stock [Member] | Series A Warrants [Member]
Class of Warrant or Right [Line Items]
Exercise price of warrants | $ / shares		$ 1.40						$ 1.40
December 2011 Financing [Member] | Capital Units [Member] | Series A Warrants [Member]
Class of Warrant or Right [Line Items]
Number of securities callable by each warrant or right warrants		1						1
December 2011 Financing [Member] | Capital Units [Member] | Series B Warrant [Member]
Class of Warrant or Right [Line Items]
Number of securities callable by each warrant or right warrants		1						1
Warrant expiration				December 2016
April 2015 Financing [Member] | Common Stock [Member] | Series A Warrants [Member]
Class of Warrant or Right [Line Items]
Exercise price of warrants | $ / shares	$ 0.6999999