Loss Per Common Share - Computation of Basic and Diluted Net Loss Per Common Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Numerator:
Net loss	$ (11,540)	$ (5,591)
Adjustments for basic net loss per common share:
Dividend accrued on redeemable preferred stock	(7,256)
Dividend requirements	(75)	(75)
Net loss attributable to common stockholders	$ (19,367)	$ (13,603)
Denominator:
Denominator for basic and dilutive net loss per common share - adjusted weighted-average shares	27,959,024	27,518,782
Basic and dilutive net loss per common share:	$ (0.69)	$ (0.49)
Series E Redeemable Preferred Stock [Member]
Adjustments for basic net loss per common share:
Dividend accrued on redeemable preferred stock	$ (7,256)	$ (6,338)
Accretion of redeemable preferred stock	(496)	(1,599)
Series B Preferred Stock [Member]
Adjustments for basic net loss per common share:
Dividend requirements	(60)	(60)
Series D Preferred Stock [Member]
Adjustments for basic net loss per common share:
Dividend requirements	$ (15)	$ (15)