Schedule I - Condensed Financial Information of Registrant - Condensed Statements of Income, Parent Company (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Income
Other Income (Expense), net	$ 2,037	$ 2,900	$ 6,055
Expense
Total Operating Expenses	1,069,770	947,136	742,221
Interest Charges	36,016	37,771	34,447
Nonservice Cost Components of Postretirement Benefits	(1,075)	2,016	3,437
Income Before Income Taxes	357,535	212,821	116,057
Income Tax Expense (Benefit)	(73,351)	(36,052)	(20,206)
Net Income	284,184	176,769	95,851
OTC
Income
Equity Income in Earnings of Subsidiaries	296,833	188,375	106,379
Interest Income from Subsidiaries	3,382	2,826	2,859
Other Income (Expense), net	466	1,290	1,317
Total Income	300,681	192,491	110,555
Expense
Total Operating Expenses	17,269	14,825	14,007
Interest Charges	4,066	4,727	4,599
Interest Charges from Subsidiaries	5	3	136
Nonservice Cost Components of Postretirement Benefits	1,023	1,097	1,150
Total Expense	22,363	20,652	19,892
Income Before Income Taxes	278,318	171,839	90,663
Income Tax Expense (Benefit)	5,866	4,930	5,188
Net Income	$ 284,184	$ 176,769	$ 95,851