Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Comprehensive Income (Loss), Net of Tax, Attributable to Parent [Abstract]
Net Income	$ 655,892	$ 466,979	$ 34,110
Actuarially Determined Long-Term Liability Adjustments:
Amortization of Prior Service Credits (net of tax: $537, $561, $601)	(1,868)	(1,844)	(1,804)
Recognized Net Actuarial (Gain) Loss (net of tax: $512, $(2,459), $(5,122))	(1,782)	8,076	15,374
Settlement Loss Recognized (net of tax: $—, $—, $(6))	0	0	16
Other Comprehensive Gain before Reclassifications (net of tax: $(1,232), $(30,516), $(21,979))	4,150	99,164	65,617
Available-for-Sale Securities:
Unrealized Gain on Investments in Available-for-Sale Securities (net of tax: $23, $—, $—)	80	0	0
Derivative Instruments:
Unrealized Gain on Cash Flow Hedges (net of tax: $—, $116, $596)	0	401	1,721
Other Comprehensive Income	580	105,797	80,924
Comprehensive Income	$ 656,472	$ 572,776	$ 115,034