Convertible Preferred Stock - Additional Information (Detail) (USD $)	12 Months Ended	24 Months Ended			12 Months Ended		24 Months Ended	1 Months Ended	12 Months Ended		1 Months Ended	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2009	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2013 Series A Convertible Preferred Stock [Member]	Dec. 31, 2012 Series A Convertible Preferred Stock [Member]	Dec. 31, 2009 Series A Convertible Preferred Stock [Member]	Apr. 30, 2010 Series B Convertible Preferred Stock [Member]	Dec. 31, 2013 Series B Convertible Preferred Stock [Member]	Dec. 31, 2012 Series B Convertible Preferred Stock [Member]	Nov. 30, 2011 Series C Convertible Preferred Stock [Member]	Dec. 31, 2013 Series C Convertible Preferred Stock [Member]	Dec. 31, 2012 Series C Convertible Preferred Stock [Member]	Nov. 30, 2011 Series C- One Convertible Preferred Stock [Member]	Nov. 30, 2011 Series C-Two Convertible Preferred Stock [Member]
Class of Stock [Line Items]
Number of preferred stock sold			0	0	0	33,188,889	33,188,889	5,190,551	0	5,190,551	15,882,389	0	15,882,389	7,395,829	8,486,560
Preferred stock per share							$ 1.00	$ 1.70			$ 4.91
Preferred stock aggregate proceeds	$ 77,301,000						$ 33,100,000	$ 8,800,000			$ 78,000,000
Conversion of the principal and interest of convertible notes		2,000,000
Preferred stock fair value per share considered as premium								$ 1.11
Common stock shares outstanding			19,731,564
Preferred stock shares outstanding			0	0	0	33,188,889			0	5,190,551		0	15,882,389
Cumulative dividend per share					$ 0.060000				$ 0.100000			$ 0.294666
Dividends accrued but unpaid					$ 8,900,000	$ 7,800,000			$ 1,700,000	$ 1,400,000		$ 8,000,000	$ 5,300,000