Condensed Consolidated Statements of Operations (Unaudited) - USD ($) shares in Thousands, $ in Thousands		3 Months Ended
		Mar. 31, 2021	Mar. 31, 2020
Income Statement [Abstract]
Revenues		$ 354,193	$ 208,880
Costs and expenses:
Cost of goods sold		169,302	172,046
Selling, general and administrative expenses		16,758	14,207
Total costs and expenses		186,060	186,253
Operating income		168,133	22,627
Interest expense, net	[1],[2]	(3,574)	(3,698)
Pension settlement charge			(42,988)
Non-operating pension and other postretirement employee benefit costs		(3,414)	(3,635)
Income (loss) before income taxes		161,145	(27,694)
Income taxes		(30,039)	10,862
Net income (loss)		$ 131,106	$ (16,832)
Net income (loss) per share:
Basic (in dollars per share)		$ 1.95	$ (0.25)
Diluted (in dollars per share)		1.94	(0.25)
Dividends per share (in dollars per share)		$ 0.41	$ 0.40
Weighted-average shares outstanding:
Basic (in shares)		67,207	67,478
Diluted (in shares)		67,607	67,478

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

[2] Realized losses on interest rate contracts consist of net cash received or paid and interest accruals on the interest rate swaps during the periods. Net cash received or paid is included in the supplemental cash flow information within interest, net of amounts capitalized in the Condensed Consolidated Statements of Cash Flows.