Commitments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 1996
Property Subject to or Available for Operating Lease [Line Items]
Term of lease				15 years
Capital leased property	$ 30,832	$ 30,829
Proceeds from assignment of purchase option under lease				$ 1,700
Increase in capital leased property				5,700
Capital lease obligations				22,000
Increase in capital lease obligations				6,700
Net book value of capital asset				18,300
Capital Leases, Future Minimum Payments, Present Value of Net Minimum Payments, Fiscal Year Maturity [Abstract]
2018	1,948
2019	1,996
2020	2,046
2021	2,099
2022	2,149
Remainder	15,118
Total minimum obligations	25,356
Less amounts representing interest (ranging from 5.8% to 18.8%)	(6,363)
Net present value of minimum obligations	18,993
Less current portion	(1,013)	(918)
Capital lease obligations	17,980	18,990
Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
2018	516
2019	494
2020	507
2021	503
2022	366
Remainder	354
Total minimum lease payments	2,740
Rent expense charged to operations	1,600	1,700	$ 1,800
Movement in Standard and Extended Product Warranty, Increase (Decrease) [Roll Forward]
Balance Beginning of Year	51	133	189
Accruals	0	279	125
Warranty Expenses	(21)	(361)	(181)
Balance End of Year	$ 30	51	$ 133	$ 189
Capital Lease Obligations [Member]
Capital Leases, Future Minimum Payments, Present Value of Net Minimum Payments, Fiscal Year Maturity [Abstract]
Annual rent increase percentage	2.50%
Accumulated amortization for property and equipment under capital leases	$ 16,300	$ 15,700
Capital Lease Obligations [Member] | Minimum [Member]
Capital Leases, Future Minimum Payments, Present Value of Net Minimum Payments, Fiscal Year Maturity [Abstract]
Interest rate percentage	5.00%
Capital Lease Obligations [Member] | Maximum [Member]
Capital Leases, Future Minimum Payments, Present Value of Net Minimum Payments, Fiscal Year Maturity [Abstract]
Interest rate percentage	21.80%
Property [Member]
Capital Leases, Future Minimum Payments, Present Value of Net Minimum Payments, Fiscal Year Maturity [Abstract]
2018	$ 1,947
2019	1,995
2020	2,045
2021	2,097
2022	2,149
Remainder	15,118
Total minimum obligations	25,351
Less amounts representing interest (ranging from 5.8% to 18.8%)	(6,361)
Net present value of minimum obligations	18,990
Less current portion	(1,012)
Capital lease obligations	17,978
Property [Member] | Capital Lease Obligations [Member]
Property Subject to or Available for Operating Lease [Line Items]
Term of lease					13 years	20 years
Capital leased property						$ 12,300
Increase in capital leased property					$ 11,700
Capital lease obligations					15,500
Net book value of capital asset					$ 13,100
Equipment [Member]
Capital Leases, Future Minimum Payments, Present Value of Net Minimum Payments, Fiscal Year Maturity [Abstract]
2018	1
2019	1
2020	1
2021	2
2022	0
Remainder	0
Total minimum obligations	5
Less amounts representing interest (ranging from 5.8% to 18.8%)	(2)
Net present value of minimum obligations	3
Less current portion	(1)
Capital lease obligations	$ 2