Commitments (Details) - USD ($)		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 1996
Weighted Average Remaining Lease Term [Abstract]
Operating leases		2 years 6 months	3 years 6 months
Finance leases		8 years 3 months 18 days	9 years 3 months 18 days
Weighted Average Discount Rate [Abstract]
Operating leases		5.75%
Finance leases		5.04%
Operating Leases, Right-of-Use Assets and Lease Liabilities [Abstract]
Right-of-use asset		$ 1,464,000	$ 1,979,000
Capital Lease Obligations [Abstract]
Term of lease					15 years
Capital leased property		30,792,000	30,792,000
Proceeds from assignment of purchase option under lease					$ 1,700,000
Increase in capital leased property					5,700,000
Capital lease obligations					22,000,000
Increase in capital lease obligations					6,700,000
Net book value of capital asset					$ 18,300,000
Future Minimum Lease Commitments [Abstract]
2021		752,000
2022		592,000
2023		373,000
2024		27,000
2025		0
After 2025		0
Total lease payments		1,744,000
Less imputed interest		(126,000)
Total		1,618,000
Less current portion		(677,000)	(602,000)
Long-term lease obligations, Operating leases		$ 941,000	1,553,000
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]		Less current portion
Finance Lease Liabilities, Payments, Due [Abstract]
2021		$ 2,097,000
2022		2,149,000
2023		2,202,000
2024		2,258,000
2025		2,314,000
After 2025		8,344,000
Total lease payments		19,364,000
Less imputed interest		(3,724,000)
Total		15,640,000
Less current portion		(1,339,000)
Long-term lease obligations, Finance leases		14,301,000
Lease, Cost [Abstract]
Operating lease cost		724,000	597,000
Short-term lease cost	[1]	93,000	147,000
Finance Lease Costs [Abstract]
Amortization of finance lease assets		1,221,000	1,221,000
Interest on finance lease liabilities		822,000	881,000
Total finance lease cost		2,043,000	2,102,000
Total lease costs		2,860,000	2,846,000
Cash paid for amounts included in the measurement of lease liabilities: [Abstract]
Cash flows from operating activities - operating leases		745,000	604,000
Cash flows from operating activities - finance leases		820,000	880,000
Cash flows from financing activities - finance leases		1,225,000	1,115,000
Operating lease right-of-use assets obtained in exchange for operating lease liabilities		613,000	488,000
Rent expense charged to operations		1,100,000	1,200,000	$ 1,600,000
Warranties [Abstract]
Accrued warranties		30,000	30,000
Accruals		$ 0	$ 0	$ 0
Capital Lease Obligations [Member]
Capital Lease Obligations [Abstract]
Annual rent increase percentage		2.50%
Property [Member] | Capital Lease Obligations [Member]
Capital Lease Obligations [Abstract]
Term of lease						13 years	20 years
Capital leased property							$ 12,300,000
Increase in capital leased property						$ 11,700,000
Capital lease obligations						15,500,000
Net book value of capital asset						$ 13,100,000

[1] Leases that have terms of 12 months or less.