Property and Equipment, Net - (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Property and Equipment, Net
Property and equipment, gross	$ 15,943,000		$ 15,943,000		$ 13,876,000
Less: accumulated depreciation and amortization	(3,614,000)		(3,614,000)		(2,469,000)
Property and equipment, net	12,329,000		12,329,000		11,407,000
Depreciation and amortization expense	582,000	$ 387,000	1,145,000	$ 763,000
Research equipment
Property and Equipment, Net
Property and equipment, gross	9,348,000		9,348,000		7,787,000
Leasehold improvements
Property and Equipment, Net
Property and equipment, gross	5,065,000		5,065,000		4,825,000
Computer equipment
Property and Equipment, Net
Property and equipment, gross	360,000		360,000		167,000
Furniture and fixtures
Property and Equipment, Net
Property and equipment, gross	93,000		93,000		70,000
Construction in progress
Property and Equipment, Net
Property and equipment, gross	$ 1,077,000		$ 1,077,000		$ 1,027,000