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Income Taxes (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Operating Loss Carryforwards [Line Items]
U.S federal corporate tax rate	21.00%	21.00%
Valuation allowance increase (decrease)	$ (1,300)
Unrecognized tax benefits	4,500	$ 4,400	$ 4,400
Write Down Of Share-Based Compensation [Member]
Operating Loss Carryforwards [Line Items]
Valuation allowance increase (decrease)	(2,400)
Book Losses [Member]
Operating Loss Carryforwards [Line Items]
Valuation allowance increase (decrease)	1,100	$ 900
Federal [Member]
Operating Loss Carryforwards [Line Items]
Pre-tax net operating loss carryforwards	87,300
Federal [Member] | Expires Between 2029 And 2039 [Member]
Operating Loss Carryforwards [Line Items]
Pre-tax net operating loss carryforwards	74,100
Federal [Member] | Indefinitely [Member]
Operating Loss Carryforwards [Line Items]
Pre-tax net operating loss carryforwards	13,200
Federal [Member] | Expires Between 2023 And 2039 [Member]
Operating Loss Carryforwards [Line Items]
Federal research and development tax credits	$ 11,100
Federal [Member] | Minimum [Member] | Expires Between 2029 And 2039 [Member]
Operating Loss Carryforwards [Line Items]
Expiration date of pre-tax net operating loss carryforwards	Jan. 01, 2029
Federal [Member] | Minimum [Member] | Expires Between 2023 And 2039 [Member]
Operating Loss Carryforwards [Line Items]
Expiration date of federal research and development tax credits	Jan. 01, 2023
Federal [Member] | Maximum [Member] | Expires Between 2029 And 2039 [Member]
Operating Loss Carryforwards [Line Items]
Expiration date of pre-tax net operating loss carryforwards	Dec. 31, 2039
Federal [Member] | Maximum [Member] | Expires Between 2023 And 2039 [Member]
Operating Loss Carryforwards [Line Items]
Expiration date of federal research and development tax credits	Dec. 31, 2040

X

- Definition

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

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