Restructuring Charges - Summary of Components of Restructuring Activity (Detail) $ in Thousands	6 Months Ended
	Jun. 30, 2018 USD ($)
Restructuring Cost And Reserve [Line Items]
Amounts accrued at December 31, 2017	$ 355
Amounts paid	(206)
Amounts accrued at June 30, 2018	149
Employee Severance, Benefits and Related Costs [Member]
Restructuring Cost And Reserve [Line Items]
Amounts accrued at December 31, 2017	72
Amounts paid	(72)
Obligations under Manufacturing and Development Contracts [Member]
Restructuring Cost And Reserve [Line Items]
Amounts accrued at December 31, 2017	283
Amounts paid	(134)
Amounts accrued at June 30, 2018	$ 149