STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Statement of Comprehensive Income [Abstract]
Net income	$ 297,860	$ 293,304	$ 316,821
Other comprehensive income, net of tax
Change in unrealized holding (losses) gains on available-for-sale securities	(17,112)	18,738	11,718
Pension and other postretirement plans	69,967	19,987	1,698
Total other comprehensive income, net of tax	52,855	38,725	13,416
Comprehensive income	$ 350,715	$ 332,029	$ 330,237