Financial Instruments - Allowance for Credit Losses and Investment in Financing Receivables (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Allowance for credit losses:
Beginning balance			$ 994
Ending balance	$ 1,070		1,070
Net Investment in Leases [Member]
Allowance for credit losses:
Beginning balance	155	$ 155	155	$ 155
Charge-offs	0	0	0	0
Recoveries	0	0	0	0
Provision	0	0	0	0
Ending balance	155	155	155	155
Ending balance: individually evaluated for impairment	155	155	155	155
Financing receivables:
Ending balance: individually evaluated for impairment	11,651	8,943	11,651	8,943
Net Financed Sales Receivables [Member]
Allowance for credit losses:
Beginning balance	839	839	839	922
Charge-offs	0	0	0	(183)
Recoveries	0	0	0	0
Provision	76	0	76	100
Ending balance	915	839	915	839
Ending balance: individually evaluated for impairment	915	839	915	839
Financing receivables:
Ending balance: individually evaluated for impairment	$ 110,759	$ 118,369	$ 110,759	$ 118,369