Consolidated 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	$ 52,754	$ 35,934	$ 125,152	$ 77,183
Unrealized Gain (Loss) on Available-for-Sale Securities:
Reversal of Previously Recognized Losses (Gains) Realized on Sale of Investments and Included in Other Income (Expense)	0	(21)	(43)	13
Unrealized Gains (Losses)	(33)	(13)	(85)	205
Income Tax (Expense) Benefit	7	7	27	(46)
Available-for-Sale Securities, net of tax	(26)	(27)	(101)	172
Pension and Postretirement Benefit Plans:
Amortization of Unrecognized Postretirement Benefit Losses and Costs	197	138	591	413
Income Tax Expense	(51)	(36)	(154)	(108)
Pension and Postretirement Benefit Plan, net of tax	146	102	437	305
Total Other Comprehensive Income	120	75	336	477
Total Comprehensive Income	$ 52,874	$ 36,009	$ 125,488	$ 77,660