Net Loss Per Share - Reconciliation of Numerator and Denominator Used in Computing Basic and Diluted Net Loss per Share (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Numerator:
Net loss									$ (29,281)	$ (17,708)	$ (10,932)
Accretion of mandatorily redeemable convertible preferred stock									(4,653)	(7,533)	(5,251)
Net loss attributable to common stockholders	$ (8,827)	$ (7,700)	$ (7,806)	$ (9,601)	$ (7,879)	$ (6,544)	$ (5,415)	$ (5,403)	$ (33,934)	$ (25,241)	$ (16,183)
Denominator:
Weighted-average common shares outstanding-basic and diluted									7,643	355	323