Revenue Recognition (Details)	3 Months Ended		6 Months Ended
	Jun. 30, 2022 USD ($)	Jun. 30, 2021 USD ($)	Jun. 30, 2022 USD ($) service member	Jun. 30, 2021 USD ($)	Dec. 31, 2021 USD ($)
Revenue Recognition
Number of electric distribution cooperative members | member			38
Number of services provided | service			2
Member energy requirements supplied	59.00%	62.00%	58.00%	59.00%
Margins for interest ratio			1.10
Targeted margins for interest ratio			1.14
Refund liability	$ 5,000,000	$ 4,500,000	$ 5,000,000	$ 4,500,000
Operating revenues	533,128,000	358,127,000	953,570,000	734,458,000
Members
Revenue Recognition
Operating revenues	478,782,000	357,921,000	896,231,000	734,193,000
Receivables from contracts	218,953,000		218,953,000		$ 143,715,000
Non-Members
Revenue Recognition
Operating revenues	54,346,000	206,000	57,339,000	265,000
Receivables from contracts	21,235,000		21,235,000		$ 302,000
Capacity revenues | Members
Revenue Recognition
Operating revenues	241,841,000	232,431,000	485,132,000	488,255,000
Energy revenues | Members
Revenue Recognition
Operating revenues	236,941,000	125,490,000	411,099,000	245,938,000
Energy revenues | Non-Members
Revenue Recognition
Operating revenues	$ 54,346,000	$ 206,000	$ 57,339,000	$ 265,000