Loss Per Share - Calculation of Loss Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Earnings Per Share [Abstract]
Net loss	$ (4,538)	$ (6,803)	$ (6,669)	$ (11,755)
Dividends related to 7% Series B convertible preferred stock	(200)	(100)	(300)	(300)
Net loss available to common stockholders	$ (4,684)	$ (6,949)	$ (6,961)	$ (12,047)
Per share of common stock:
Basic/diluted net loss available to common stockholders	$ (0.15)	$ (0.22)	$ (0.22)	$ (0.41)
Weighted average shares outstanding (basic and diluted)	31,927	31,336	31,837	29,379
Anti-dilutive common stock equivalents	1,481	1,120	1,487	1,660