Computation of Basic and Diluted Loss per Share under Two-Class Method (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Numerator for basic and diluted loss per share:
Net loss	$ (22,272)	$ (32,444)
Effect of reallocating undistributed earnings of participating securities	0	0
Net loss available under the two-class method	$ (22,272)	$ (32,444)
Denominator:
Denominator for basic loss per share--weighted-average shares	26,788,591	26,607,377
Effect of dilutive potential common shares	0	0
Denominator for diluted loss per share--adjusted weighted-average shares	26,788,591	26,607,377
Basic loss per share	$ (0.83)	$ (1.22)
Diluted loss per share	$ (0.83)	$ (1.22)