Revenue Recognition - Sales to Members & Non-Members (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Revenue Recognition
Total operating revenues	$ 564,090	$ 389,389	$ 1,100,404	$ 778,842
Sales to members
Revenue Recognition
Total operating revenues	562,267	365,496	1,097,637	753,149
Sales to members | Capacity revenues
Revenue Recognition
Total operating revenues	401,710	234,183	757,428	476,227
Sales to members | Energy revenues
Revenue Recognition
Total operating revenues	160,557	131,313	340,209	276,922
Sales to non-members
Revenue Recognition
Total operating revenues	1,823	23,893	2,767	25,693
Sales to non-members | Capacity revenues
Revenue Recognition
Total operating revenues	786	3,624	1,572	4,387
Sales to non-members | Energy revenues
Revenue Recognition
Total operating revenues	$ 1,037	$ 20,269	$ 1,195	$ 21,306