Fair Value of Financial Instruments (Details-3)	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Basis adjustment:
Basis adjustment - on peak	92.10%	92.10%
Basis adjustment - off peak	92.50%	92.80%
US Treasury Bill Securities [Member]
Deferred compensation plan [Abstract]
Investment interest calculation, investment maturity period (26 weeks)	182 days
Investment interest calculation, monthly compounding rate	1.00%
Investment interest calculation, minimum annual rate compounded monthly	7.00%
Minimum [Member]
Counterparty fuel mix:
Internal generation	40.00%	50.00%
Purchased power	40.00%	25.00%
Maximum [Member]
Counterparty fuel mix:
Internal generation	60.00%	75.00%
Purchased power	60.00%	50.00%