Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Operating revenues	$ 373,466	$ 356,009	$ 1,513,898	$ 1,422,143	$ 1,477,837
Operating income	91,696	103,163	323,321	300,455	263,079
Net Income	$ 80,552	$ 83,142	$ 224,111	$ 194,131	$ 183,008
Average Common Shares Outstanding	61,315,000	61,244,000	61,293,052	60,321,481	55,769,156
Income per average common share
Income per average common share, basic	$ 1.32	$ 1.37	$ 3.66	$ 3.22	$ 3.28
Income per average common share, diluted	$ 1.31	$ 1.37	$ 3.65	$ 3.22	$ 3.25