STATEMENTS OF COMPREHENSIVE INCOME STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Net income	$ 206,434	$ 196,412	$ 186,749
Other Comprehensive Income (Loss), Net of Tax [Abstract]
Change in pension and other postretirement benefit plans liability, net of tax of $(379), $289, and $479, respectively	1,250	(1,038)	(1,435)
Other comprehensive income (loss), net of tax	1,250	(1,038)	(1,435)
Comprehensive income	207,684	195,374	185,314
Pension and other postretirement benefit plans, Tax	$ (379)	$ 289	$ 479