Significant Accounting Policies - Credit Losses - ASU 2016-13 (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2020	Dec. 31, 2019
Accounts Receivable, Noncurrent, Credit Quality Indicator [Line Items]
Accounts Receivable, Allowance for Credit Loss	$ 1,592	$ 673
Accounts Receivable, Allowance for Credit Loss, Period Increase (Decrease)	1,232
Accounts Receivable, Allowance for Credit Loss, Writeoff	(313)
Residential [Member]
Accounts Receivable, Noncurrent, Credit Quality Indicator [Line Items]
Accounts Receivable, Allowance for Credit Loss	1,013	432
Accounts Receivable, Allowance for Credit Loss, Period Increase (Decrease)	817
Accounts Receivable, Allowance for Credit Loss, Writeoff	(236)
Commercial [Member]
Accounts Receivable, Noncurrent, Credit Quality Indicator [Line Items]
Accounts Receivable, Allowance for Credit Loss	337	57
Accounts Receivable, Allowance for Credit Loss, Period Increase (Decrease)	349
Accounts Receivable, Allowance for Credit Loss, Writeoff	(69)
Industrial [Member]
Accounts Receivable, Noncurrent, Credit Quality Indicator [Line Items]
Accounts Receivable, Allowance for Credit Loss	100	72
Accounts Receivable, Allowance for Credit Loss, Period Increase (Decrease)	34
Accounts Receivable, Allowance for Credit Loss, Writeoff	(6)
Accrued unbilled and other [Member]
Accounts Receivable, Noncurrent, Credit Quality Indicator [Line Items]
Accounts Receivable, Allowance for Credit Loss	142	$ 112
Accounts Receivable, Allowance for Credit Loss, Period Increase (Decrease)	32
Accounts Receivable, Allowance for Credit Loss, Writeoff	$ (2)