STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Statement of Comprehensive Income [Abstract]
Net income	$ 90,223	$ 89,216	$ 242,818	$ 230,519
Other comprehensive (loss) income, net of tax
Change in unrealized holding (losses) gains on available-for-sale securities	(3,732)	6,143	(9,808)	11,358
Amortization of prior service costs and net actuarial loss on pension and other postretirement plans	3,463	2,659	10,389	7,979
Total other comprehensive (loss) income, net of tax	(269)	8,802	581	19,337
Comprehensive income	$ 89,954	$ 98,018	$ 243,399	$ 249,856