Convertible Preferred Stock - Additional Information (Detail) (USD $)					3 Months Ended		9 Months Ended		99 Months Ended																												0 Months Ended	3 Months Ended		9 Months Ended		31 Months Ended
	Sep. 30, 2013	Dec. 31, 2012	Dec. 07, 2012	Feb. 28, 2011	Sep. 30, 2013 Convertible Preferred Stock [Member]	Sep. 30, 2012 Convertible Preferred Stock [Member]	Sep. 30, 2013 Convertible Preferred Stock [Member]	Sep. 30, 2012 Convertible Preferred Stock [Member]	Sep. 30, 2013 Convertible Preferred Stock [Member]	Feb. 28, 2011 Convertible Preferred Stock [Member]	Sep. 30, 2013 Convertible Preferred Stock Series A-1 [Member]	Dec. 31, 2012 Convertible Preferred Stock Series A-1 [Member]	Feb. 28, 2011 Convertible Preferred Stock Series A-1 [Member]	Sep. 30, 2013 Convertible Preferred Stock Series A-2 [Member]	Dec. 31, 2012 Convertible Preferred Stock Series A-2 [Member]	Feb. 28, 2011 Convertible Preferred Stock Series A-2 [Member]	Sep. 30, 2013 Convertible Preferred Stock Series A-3 [Member]	Dec. 31, 2012 Convertible Preferred Stock Series A-3 [Member]	Feb. 28, 2011 Convertible Preferred Stock Series A-3 [Member]	Sep. 30, 2013 Convertible Preferred Stock Series A-4 [Member]	Dec. 31, 2012 Convertible Preferred Stock Series A-4 [Member]	Feb. 28, 2011 Convertible Preferred Stock Series A-4 [Member]	Sep. 30, 2013 Convertible Preferred Stock Series B [Member]	Dec. 31, 2012 Convertible Preferred Stock Series B [Member]	Feb. 28, 2011 Convertible Preferred Stock Series B [Member]	Sep. 30, 2013 Series A-1 Preferred Stock [Member]	Dec. 07, 2012 Series A-1 Preferred Stock [Member]	Sep. 30, 2013 Series A-2 Preferred Stock [Member]	Dec. 07, 2012 Series A-2 Preferred Stock [Member]	Sep. 30, 2013 Series A-3 Preferred Stock [Member]	Dec. 07, 2012 Series A-3 Preferred Stock [Member]	Sep. 30, 2013 Series A-4 Preferred Stock [Member]	Dec. 07, 2012 Series A-4 Preferred Stock [Member]	Sep. 30, 2013 Series B Preferred Stock [Member]	Dec. 07, 2012 Series B Preferred Stock [Member]	Sep. 16, 2013 Series B Convertible Preferred Stock [Member]	Feb. 23, 2011 Series A-4 Convertible Preferred Stock [Member]	Sep. 30, 2013 Series A-4 Convertible Preferred Stock [Member]	Sep. 30, 2012 Series A-4 Convertible Preferred Stock [Member]	Sep. 30, 2013 Series A-4 Convertible Preferred Stock [Member]	Sep. 30, 2012 Series A-4 Convertible Preferred Stock [Member]	Sep. 30, 2013 Series A-4 Convertible Preferred Stock [Member]
Permanent And Temporary Equity [Line Items]
Common stock, shares authorized	22,000,000	20,000,000	20,000,000	15,734,582
Convertible preferred stock, shares authorized	87,872,909	82,672,909	82,672,909							63,672,909	2,000,000	2,000,000	2,000,000	10,010,029	10,010,029	10,010,029	22,479,476	22,479,476	23,266,976	5,683,404	5,683,404	4,895,904	47,700,000	42,500,000	23,500,000	2,000,000	2,000,000	10,010,029	10,010,029	22,479,476	22,479,476	5,683,404	5,683,404	50,000,000	42,500,000
Authorized Convertible Preferred Stock Shares Re-designated to Authorized Common Stock Shares																																				2,300,000
Accretion amount					$ 65,000	$ 65,000	$ 193,000	$ 193,000	$ 722,000																													$ 74,000	$ 73,000	$ 220,000	$ 219,000	$ 755,000
Difference between stated and fair value																																					$ 1,300,000