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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Amount of minimum lease payments for capital leases.

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Amount necessary to reduce net minimum lease payments to present value for capital leases.

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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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The aggregate amount of write-downs for impairments recognized during the period for long-lived assets held for abandonment, exchange or sale.

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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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Property and equipment, net - Depreciation and amortization (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Property, Plant and Equipment [Line Items]
Depreciation and amortization expense	$ 400,000	$ 300,000	$ 1,079,000	$ 1,190,000
Fully depreciated assets disposed of	0	$ 0		$ 0
Property plant and equipment, gross	20,024,000		20,024,000		$ 17,388,000
Accumulated depreciation	11,391,000		11,391,000		10,336,000
Assets held under capital leases
Property, Plant and Equipment [Line Items]
Property plant and equipment, gross	400,000		400,000		0
Accumulated depreciation	100,000		100,000		$ 0
Capital lease future minimum payment due	600,000		600,000
Capital lease future minimum payment due, interest	$ 200,000		200,000
Maximum
Property, Plant and Equipment [Line Items]
Fully depreciated assets disposed of			$ 100,000