Computation of Basic and Diluted Loss per Share under Two-Class Method (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Numerator for basic and diluted loss per share:
Net loss	$ (14,812)	$ (24,822)	$ (37,084)	$ (57,266)
Effect of reallocating undistributed earnings of participating securities	0	0	0	0
Net loss available under the two-class method	$ (14,812)	$ (24,822)	$ (37,084)	$ (57,266)
Denominator:
Denominator for basic loss per share--weighted-average shares	26,930,914	26,665,092	26,860,146	26,636,394
Effect of dilutive potential common shares	0	0	0	0
Denominator for diluted loss per share--adjusted weighted-average shares	26,930,914	26,665,092	26,860,146	26,636,394
Basic loss per share	$ (0.55)	$ (0.93)	$ (1.38)	$ (2.15)
Diluted loss per share	$ (0.55)	$ (0.93)	$ (1.38)	$ (2.15)