Difference between Benefit from Income Taxes and Amount Computed by Applying Statutory Income Tax Rate to Income Before Taxes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Benefits from taxes at statutory rate	$ (13,698)	$ (19,039)	$ (29,572)
Rate differential	3,071	4,667	8,572
Change in valuation reserves	22,115	13,276	8,719
Derivative liabilities		(668)	187
Gain on extinguishment of debt			(328)
Nondeductible employee compensation	1,668	1,164	808
Stock option/RSU windfall	(1,182)
Research and development credits	(1,177)	(1,689)	(1,284)
Tax return to provision adjustments	5,788	4,524	2,248
U.S. rate change—tax reform	7,398
Cumulative translation adjustment	(12,554)	7,385	7,811
Permanent and other	1,635	(1,573)	(1,841)
Non-deductible interest expense	(17)	1,922	1,594
Provision for (benefit from) income taxes	$ 13,047	$ 9,969	$ (3,086)