Commitments - Additional Information (Detail) - USD ($)		12 Months Ended
	Aug. 22, 2008	Dec. 31, 2017	Dec. 31, 2016
Commitments and Contingencies Disclosure [Abstract]
Rent expense		$ 1,900,000	$ 1,300,000
BioValve
Commitments And Contingencies [Line Items]
Licensing payment	9.00%
Licensing payment	10.00%
Amounts owed		$ 0	$ 0