Amount of accumulated depreciation, depletion and amortization for physical assets used in the normal conduct of business to produce goods and services.

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The aggregate expense recognized in the current period that allocates the cost of tangible assets, intangible assets, or depleting assets to periods that benefit from use of the assets.

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Amount before accumulated depreciation, depletion and amortization of physical assets used in the normal conduct of business and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures.

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Amount after accumulated depreciation, depletion and amortization of physical assets used in the normal conduct of business to produce goods and services and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures.

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Property and Equipment, Net - (Details) - USD ($)	3 Months Ended		9 Months Ended		12 Months Ended
Property and Equipment, Net - (Details) - USD ($)	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018	Dec. 31, 2017
Property and Equipment, Net
Property and equipment, gross	$ 16,433,000		$ 16,433,000		$ 13,876,000	$ 10,813,000
Less: accumulated depreciation and amortization	(4,402,000)		(4,402,000)		(2,469,000)	(792,000)
Property and equipment, net	12,031,000		12,031,000		11,407,000	10,021,000
Depreciation and amortization expense	788,000	$ 396,000	1,933,000	$ 1,159,000	1,677,000	582,000
Research equipment
Property and Equipment, Net
Property and equipment, gross	9,746,000		9,746,000		7,787,000	6,213,000
Leasehold improvements
Property and Equipment, Net
Property and equipment, gross	5,365,000		5,365,000		4,825,000	564,000
Computer equipment
Property and Equipment, Net
Property and equipment, gross	441,000		441,000		167,000	111,000
Furniture and fixtures
Property and Equipment, Net
Property and equipment, gross	94,000		94,000		70,000	33,000
Construction in progress
Property and Equipment, Net
Property and equipment, gross	$ 787,000		$ 787,000		$ 1,027,000	$ 3,892,000