Reconciliation of Weighted Average Shares Used in Computation of Loss Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Earnings Per Share Disclosure [Line Items]
Net loss available to common stockholders	$ (36,244)	$ (18,316)
Shares used in loss per share	23,100	18,104
Loss per share	$ (1.57)	$ (1.01)