Income Taxes - Schedule of Income Tax Expense (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Computed “expected” tax expense	$ (16,758)	$ (15,765)
Increase (reduction) in income taxes resulting from:
Change in the valuation allowance	(40,114)	9,506
State taxes, net of federal benefit	607	(141)
Federal research and development credits	(236)	(21)
Change in Federal Tax Rate	56,105	0
Cancellation of Options	0	3,451
Nondeductible Interest	0	1,976
Stock Compensation	0	831
Other, net	396	163
Total income tax expense/(benefit)	$ 0	$ 0