Income Taxes - Components of provision for income taxes (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Provision for income tax benefit (expense)
Income tax benefit	$ 7,000	$ (93,000)	$ 0	$ (279,000)
Provision for income taxes on undistributed earnings of foreign subsidiaries	$ 0		$ 0