Summary of Adjustment for Net Loss for Diluted Net Loss per Share Calculation (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Dilutive Securities Included In Computation Of Earnings Per Share [Line Items]
Net loss	$ (11,973)	$ (7,348)	$ (24,714)	$ (14,577)
Less: gain from change in valuation of notes payable	953	(2,697)	(1,171)	(4,458)
Net loss used to compute diluted net loss per share	$ (12,926)