Segment Information - Business Segments (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Dec. 31, 2021
Segment Reporting Information [Line Items]
Total Operating Revenues	$ 374,904	$ 261,710
Net Income (Loss)	72,003	30,329
Identifiable Assets	2,791,741		$ 2,754,830
Corporate
Segment Reporting Information [Line Items]
Net Income (Loss)	(2,160)	(1,790)
Identifiable Assets	58,706		57,445
Electric | Operating Segments
Segment Reporting Information [Line Items]
Total Operating Revenues	130,416	123,699
Net Income (Loss)	19,233	17,587
Identifiable Assets	2,278,337		2,283,776
Manufacturing | Operating Segments
Segment Reporting Information [Line Items]
Total Operating Revenues	104,957	75,825
Net Income (Loss)	4,084	5,385
Identifiable Assets	269,833		251,044
Plastics | Operating Segments
Segment Reporting Information [Line Items]
Total Operating Revenues	139,531	62,186
Net Income (Loss)	50,846	$ 9,147
Identifiable Assets	$ 184,865		$ 162,565