Debt (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Total debt, Principal	$ 30,000
Less: debt-current	(1,429)
Debt-non-current	28,387	$ 29,798
Cerus Term Loans
Debt Instrument [Line Items]
Total debt, Principal	30,000	30,000
Total debt, Unamortized Discount	(184)	(202)
Total debt	29,816	29,798
Less: debt - current, Principal	(1,429)
Less: debt-current	(1,429)
Debt - non-current, Principal	28,571	30,000
Debt - non-current, Unamortized Discount	(184)	(202)
Debt-non-current	$ 28,387	$ 29,798