Income taxes (Details) - USD ($)	3 Months Ended	9 Months Ended
Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Income Taxes
Income tax expense	$ 25,000	$ 44,000	$ 63,000	$ 2,013,000
State income tax expense	0		0
Unrecognized tax benefits	9,700,000		9,700,000		$ 8,600,000
Interest and penalties accrued	$ 0		$ 0

No definition available.

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Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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Amount of state and local current and deferred income tax expense (benefit) attributable to continuing operations.

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Amount of unrecognized tax benefits.

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Amount accrued for interest on an underpayment of income taxes and penalties related to a tax position claimed or expected to be claimed in the tax return.

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