Condensed Consolidated Statements of Operations (Unaudited) - USD ($) shares in Thousands, $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Income Statement [Abstract]
Revenues		$ 359,597	$ 447,506	$ 770,947	$ 801,699
Costs and expenses:
Cost of goods sold		191,334	177,779	371,181	347,081
Selling, general and administrative expenses		20,412	19,512	36,706	36,270
Gain on fire damage		(9,868)	0	(9,592)	0
Total costs and expenses		201,878	197,291	398,295	383,351
Operating income		157,719	250,215	372,652	418,348
Interest expense, net	[1]	(7,419)	(8,199)	(10,313)	(11,773)
Pension settlement charge		0	0	(14,165)	0
Non-operating pension and other postretirement employee benefit costs		(1,809)	(3,271)	(3,738)	(6,685)
Income before income taxes		148,491	238,745	344,436	399,890
Income taxes		(28,269)	(50,840)	(60,334)	(80,879)
Net income		$ 120,222	$ 187,905	$ 284,102	$ 319,011
Net income per share:
Basic		$ 1.73	$ 2.79	$ 4.09	$ 4.74
Diluted		1.72	2.77	4.07	4.71
Dividends per share		$ 0.44	$ 0.41	$ 0.88	$ 0.82
Weighted-average shares outstanding
Basic		69,580	67,316	69,502	67,265
Diluted		69,791	67,732	69,731	67,664

[1] Bond discounts and deferred loan fees are reported within interest expense, net on the Condensed Consolidated Statements of Operations.