Prepaid Expenses and Other Current Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Deferred Costs Capitalized Prepaid And Other Assets Disclosure [Abstract]
Prepaid research and development services	$ 245	$ 384
Prepaid insurance	200	279
Other prepaid expenses	20	62
Other receivable due from R-Pharm	0	251
NOL sale receivable	6,732	0
Other current assets	54	91
Total prepaid expenses and other current assets	$ 7,251	$ 1,067