Restructuring and Severance - Additional Information (Detail) - USD ($) $ in Thousands		12 Months Ended
	Feb. 14, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Restructuring Cost And Reserve [Line Items]
Restructuring and severance expenses		$ 747	$ (49)
Restructuring accrual		$ 129		$ 237
3VR
Restructuring Cost And Reserve [Line Items]
Date of acquisition completed	Feb. 14, 2018	Feb. 14, 2018
Restructuring and severance expenses		$ 600
3VR | Facility Rental
Restructuring Cost And Reserve [Line Items]
Restructuring and severance expenses		300
3VR | Severance
Restructuring Cost And Reserve [Line Items]
Restructuring and severance expenses		$ 300