Teijin Agreement - Additional Information (Detail) - License and Supply Agreement [Member] - USD ($)	1 Months Ended		14 Months Ended
	Jan. 31, 2018	Aug. 31, 2016	Sep. 30, 2017	Dec. 31, 2018
Teijin Limited [Member]
Revenue Recognition Milestone Method [Line Items]
Payments received under license and supply agreement		$ 40,000,000	$ 40,000,000
Potential to receive development milestone		35,000,000
Agreement effective termination date	Jan. 31, 2018
Potential to receive development, regulatory and sales milestone payments before termination				$ 125,000,000
Maximum [Member]
Revenue Recognition Milestone Method [Line Items]
Costs associated with additional trials		5,000,000
Maximum [Member] | Teijin Limited [Member]
Revenue Recognition Milestone Method [Line Items]
Potential to receive regulatory milestone		55,000,000
Potential to receive sales milestone		$ 35,000,000