Indebtedness (Narrative) (Details)	6 Months Ended
	Jun. 30, 2020 USD ($)
Maximum [Member]
Line of Credit Facility [Line Items]
Letter of credit required to landlord	$ 1,250,000
Silicon Valley Bank Agreement [Member]
Line of Credit Facility [Line Items]
Totcal combined debt, maximum amount outstanding	$ 70,000,000
Upon certain conditions met, deferred loan payment period	6 months
Silicon Valley Bank Agreement [Member] | Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Line of credit, maximum borrowing capacity	$ 20,000,000
Line of credit, borrowings	$ 0
Maturity date	Aug. 01, 2024
Line of credit, revolving line of credit	$ 8,750,000
Borrowing availability threshold	$ 20,000,000
Annual facility fee	0.15%
Silicon Valley Bank Agreement [Member] | Revolving Credit Facility [Member] | Prime Rate [Member]
Line of Credit Facility [Line Items]
Applicable interest rate	5.00%
Term Loan [Member] | Silicon Valley Bank Agreement [Member]
Line of Credit Facility [Line Items]
Loan amount	$ 60,000,000
Annual commitment fee, percentage	3.00%
Accrued fee amount	$ 315,000
Financing costs	$ 446,000
Term Loan [Member] | Silicon Valley Bank Agreement [Member] | Prime Rate [Member]
Line of Credit Facility [Line Items]
Basis rate	0.75%
Interest rate	5.00%