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, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Numerator for basic and diluted loss per share:
Net loss	$ (24,822)	$ (20,296)	$ (57,266)	$ (44,980)
Effect of reallocating undistributed earnings of participating securities	0	0	0	0
Net loss available under the two-class method	$ (24,822)	$ (20,296)	$ (57,266)	$ (44,980)
Denominator:
Denominator for basic loss per share--weighted-average shares	26,665,092	23,108,889	26,636,394	23,085,725
Effect of dilutive potential common shares	0	0	0	0
Denominator for diluted loss per share--adjusted weighted-average shares	26,665,092	23,108,889	26,636,394	23,085,725
Basic loss per share	$ (0.93)	$ (0.88)	$ (2.15)	$ (1.95)
Diluted loss per share	$ (0.93)	$ (0.88)	$ (2.15)	$ (1.95)