SCHEDULE I - CONDENSED FINANCIAL INFORMATION OF PARENT - Condensed Statements of Income (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Condensed financial statements
Income before income taxes	$ 166,520	$ 102,060	$ 124,770
Income tax benefit	41,599	23,664	30,423
Net Income	$ 124,921	$ 78,396	$ 94,347
Weighted Average Number of Shares Outstanding (in shares)	36,976	36,955	36,921
Basic Earnings Per Common Share (usd per share)	$ 3.37	$ 2.12	$ 2.55
Weighted Average Number of Diluted Common Shares Outstanding (in shares)	37,077	37,039	37,010
Fully Diluted Earnings per Common Share (in USD per share)	$ 3.36	$ 2.11	$ 2.55
Dividends Paid Per Common Share (in USD per share)	$ 1.655	$ 1.525	$ 1.400
Parent Company
Condensed financial statements
Operating revenues and other income	$ 0	$ 0	$ 0
Operating expenses and other expenses	5,576	2,093	542
Loss before equity in earnings of subsidiaries and income taxes	(5,576)	(2,093)	(542)
Equity in earnings of subsidiaries	128,783	79,892	94,808
Income before income taxes	123,207	77,799	94,266
Income tax benefit	(1,714)	(597)	(81)
Net Income	$ 124,921	$ 78,396	$ 94,347
Weighted Average Number of Shares Outstanding (in shares)	36,976	36,955	36,921
Basic Earnings Per Common Share (usd per share)	$ 3.37	$ 2.12	$ 2.55
Weighted Average Number of Diluted Common Shares Outstanding (in shares)	37,077	37,039	37,010
Fully Diluted Earnings per Common Share (in USD per share)	$ 3.36	$ 2.11	$ 2.55
Dividends Paid Per Common Share (in USD per share)	$ 1.655	$ 1.525	$ 1.400