Summary of Adjustment for Net Loss for Diluted Net Loss per Share Calculation (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Dilutive Securities Included In Computation Of Earnings Per Share [Line Items]
Net loss	$ (9,798)	$ (2,164)	$ (34,512)	$ (16,741)
Less: gain from change in valuation of note payable	1,785	671	614	(3,787)
Net loss used to compute diluted net loss per share	$ (11,583)	$ (2,835)	$ (34,512)	$ (16,741)