Income Taxes - Unrecognized tax benefits (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Income Taxes
Unrecognized tax benefits that would affect tax rate	$ 0
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized Tax Benefits, Beginning Balance	2,218,000	$ 1,647,000
Additions related to current tax provisions	459,000	571,000
Unrecognized Tax Benefits, Ending Balance	2,677,000	2,218,000
Unrecognized Tax Benefits, Income Tax Penalties and Interest Expense [Abstract]
Increase (decrease) in provision related to unrecognized tax benefits interest expense	(100,000)	100,000
Interest and penalties accrued, unrecognized tax benefits	$ 200,000	$ 300,000