Summary of Significant Accounting Policies - Summary of Estimated Lives of Assets (Detail)	9 Months Ended
	Sep. 30, 2019
Computer equipment
Property, Plant and Equipment [Line Items]
Property and equipment, estimated useful lives	3 years
Furniture
Property, Plant and Equipment [Line Items]
Property and equipment, estimated useful lives	5 years
Minimum | Machinery, manufacturing and demonstration equipment
Property, Plant and Equipment [Line Items]
Property and equipment, estimated useful lives	3 years
Minimum | Leasehold improvements
Property, Plant and Equipment [Line Items]
Property and equipment, estimated useful lives	3 years
Maximum | Machinery, manufacturing and demonstration equipment
Property, Plant and Equipment [Line Items]
Property and equipment, estimated useful lives	5 years
Maximum | Leasehold improvements
Property, Plant and Equipment [Line Items]
Property and equipment, estimated useful lives	10 years