Derivative and Hedging Instruments (Details-1)	9 Months Ended		12 Months Ended
	Sep. 30, 2019 USD ($) Dth MWh MW		Dec. 31, 2018 USD ($) Dth MWh MW	Jun. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Dec. 31, 2017 USD ($)
Derivative fair values [Abstract]
Receivable, margin account balance, net of collateral posted against derivative positions	$ 1,598,000		$ 1,193,000
Collateral posted against derivative positions	700,000
Other Current Assets [Member]
Derivative fair values [Abstract]
Derivative fair value, net	1,031,000		377,000	$ 878,000	$ 894,000	$ 640,000	$ 806,000
Receivable, margin account balance, net of collateral posted against derivative positions	1,600,000		1,200,000
Commodity Contracts And Financial Transimission Rights [Member]
Derivative fair values [Abstract]
Derivative fair value, net	$ (200,000)		$ 700,000
Commodity Derivative Contracts [Member]
Gross Notional Volume of Open Derivatives
Notional amount, energy measure (in MWh) | MWh	466,760		386,440
Notional amount, decatherm measure (in Dth) | Dth	9,190,000		5,260,000
Derivative fair values [Abstract]
Asset Derivatives, fair value, gross basis	$ 749,000		$ 801,000
Liability Derivatives, fair value, gross basis	1,285,000		342,000
Collateral posted against derivative positions	724,000		0
Commodity Derivative Contracts [Member] | Other Current Assets [Member]
Derivative fair values [Abstract]
Asset Derivatives, fair value, gross basis	668,000		727,000
Liability Derivatives, fair value, gross basis	996,000	[1]	270,000
Commodity Derivative Contracts [Member] | Other Deferred Charges [Member]
Derivative fair values [Abstract]
Asset Derivatives, fair value, gross basis	81,000		74,000
Liability Derivatives, fair value, gross basis	289,000	[1]	$ 72,000
Commodity Derivative Contracts [Member] | Cash Flow Hedging [Member]
Derivative fair values [Abstract]
Collateral posted against derivative positions	$ 700,000
Energy Related Commodity Contract [Member] | Cash Flow Hedging [Member]
Derivatives Fair Value [Line Items]
Maximum term of derivative hedging contract	4 years
Financial Transmission Rights [Member]
Gross Notional Volume of Open Derivatives
Notional amount, power measure (in MW) | MW	4,282		2,252
Derivative fair values [Abstract]
Asset Derivatives, fair value, gross basis	$ 344,000		$ 241,000
Collateral posted against derivative positions	0		0
Financial Transmission Rights [Member] | Other Current Assets [Member]
Derivative fair values [Abstract]
Asset Derivatives, fair value, gross basis	344,000		241,000
Liability Derivatives, fair value, gross basis	$ 0		$ 0
PPA [Member]
Gross Notional Volume of Open Derivatives
Notional amount, power measure (in MW) | MW	1,600		2,050
Derivative fair values [Abstract]
Derivative fair value, net	$ (29,000,000.0)		$ (32,500,000)
Liability Derivatives, fair value, gross basis	28,990,000		32,530,000
Collateral posted against derivative positions	0		0
PPA [Member] | Derivative Liability (Current) [Member]
Derivative fair values [Abstract]
Liability Derivatives, fair value, gross basis	10,390,000		8,550,000
PPA [Member] | Derivative Liability (Long-term) [Member]
Derivative fair values [Abstract]
Liability Derivatives, fair value, gross basis	$ 18,600,000		$ 23,980,000

[1] As of September 30, 2019, collateral of $0.7 million was posted against and netted with derivative liability positions on the consolidated balance sheets. No collateral was posted against derivative positions as of December 31, 2018.