Significant Accounting Policies - Credit Losses - ASU 2016-13 - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Accounts Receivable, Noncurrent, Credit Quality Indicator [Line Items]
Accounts Receivable, Allowance for Credit Loss	$ 1,786	$ 673
Accounts Receivable, Allowance for Credit Loss, Period Increase (Decrease)	734
Accounts Receivable, Allowance for Credit Loss, Writeoff	379
Sales-type Lease [Member]
Accounts Receivable, Noncurrent, Credit Quality Indicator [Line Items]
Accounts Receivable, Allowance for Credit Loss, Period Increase (Decrease)	0
Residential [Member]
Accounts Receivable, Noncurrent, Credit Quality Indicator [Line Items]
Accounts Receivable, Allowance for Credit Loss	1,117	432
Accounts Receivable, Allowance for Credit Loss, Period Increase (Decrease)	506
Accounts Receivable, Allowance for Credit Loss, Writeoff	179
Commercial [Member]
Accounts Receivable, Noncurrent, Credit Quality Indicator [Line Items]
Accounts Receivable, Allowance for Credit Loss	462	57
Accounts Receivable, Allowance for Credit Loss, Period Increase (Decrease)	145
Accounts Receivable, Allowance for Credit Loss, Writeoff	260
Industrial [Member]
Accounts Receivable, Noncurrent, Credit Quality Indicator [Line Items]
Accounts Receivable, Allowance for Credit Loss	58	72
Accounts Receivable, Allowance for Credit Loss, Period Increase (Decrease)	26
Accounts Receivable, Allowance for Credit Loss, Recovery	(40)
Accrued unbilled and other [Member]
Accounts Receivable, Noncurrent, Credit Quality Indicator [Line Items]
Accounts Receivable, Allowance for Credit Loss	149	$ 112
Accounts Receivable, Allowance for Credit Loss, Period Increase (Decrease)	57
Accounts Receivable, Allowance for Credit Loss, Recovery	$ (20)