Income Taxes - reconciliation of the expected income tax (Details)		12 Months Ended
Dec. 21, 2017	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Taxes
U. S. statutory income tax rate	34.00%	21.00%	21.00%	35.00%
Non-deductible expenses:
Non-deductible stock awards		(0.70%)	(1.90%)
Non-deductible loss on contingent consideration		1.20%	(1.10%)
Others		(3.30%)	(0.30%)
Non-deductible interest expenses		(2.20%)	(1.20%)
Increase in valuation allowance		(17.20%)	(16.40%)
Tax rate differential		1.20%	(0.50%)
Effective income tax rate		0.00%	(0.40%)

Effective Income Tax Rate Reconciliation Nondeductible Expense Earn Out Shares Expense.

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Percentage on non-deductible loss on contingent consideration.

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Effective Income Tax Rate Reconciliation Nondeductible Expense Tax Rate Differential Percent.

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Represents percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to nondeductible interest expenses.

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

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Percentage of domestic federal statutory tax rate applicable to pretax income (loss).

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Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to changes in the valuation allowance for deferred tax assets.

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