Net loss per share - Schedule of Computation of Basic and Diluted Earnings Per Share (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Numerator
Net loss	$ (6,412)	$ (4,228)
Accretion for liquidation preference on preferred stock		(1,133)
Accretion for share issuance costs on preferred stock		(20)
Tax expense on preferred stock		(100)
Reversal of tax payable on preferred stock due to conversion of preferred stock		1,898
Extinguishment of remaining share issuance costs due to conversion of preferred stock		(439)
Total loss attributable to common stockholders	$ (6,412)	$ (4,022)
Denominator
Weighted average shares used to compute basic and diluted net loss per common share	10,711,967	3,148,481
Net loss per share attributable to common stockholders - basic and diluted	$ (0.60)	$ (1.28)