Consolidated Statements of Cash Flows - USD ($)		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Cash Flows from Operating Activities:
Net income		$ 461,000,000.0	$ 696,400,000	$ 738,000,000.0
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation, depletion, and amortization of intangibles		409,900,000	387,500,000	410,900,000
Amortization of deferred financing costs		2,600,000	23,400,000	8,600,000
Loss on early extinguishment of debt			22,200,000
Share-based compensation expense		30,000,000.0	30,400,000	23,500,000
Deferred income tax provision		34,700,000	60,300,000	38,700,000
Goodwill impairment		55,200,000
Net loss on impairment of assets				3,100,000
Net loss on asset disposals		6,800,000	8,200,000	5,800,000
Pension and post-retirement benefits expense, net of contributions		(63,400,000)	(26,900,000)	3,100,000
Other, net		18,200,000	(3,400,000)	1,300,000
Decrease (increase) in assets —
Accounts receivable		13,200,000	56,400,000	(56,100,000)
Inventories		6,300,000	1,400,000	(35,600,000)
Prepaid expenses and other current assets		400,000	(6,900,000)	(2,100,000)
Increase (decrease) in liabilities —
Accounts payable		39,700,000	(32,400,000)	(17,600,000)
Accrued liabilities		(3,200,000)	(100,000)	5,500,000
Federal and state income tax payable / receivable		21,400,000	(9,100,000)	53,000,000.0
Net cash provided by operating activities		1,032,800,000	1,207,400,000	1,180,100,000
Cash Flows from Investing Activities:
Additions to property, plant, and equipment	[1]	(421,200,000)	(399,500,000)	(551,400,000)
Acquisitions of businesses, net of cash acquired				(56,300,000)
Additions to other long-term assets		(6,400,000)	(3,800,000)	(4,500,000)
Proceeds from asset disposals		4,600,000	4,100,000	1,500,000
Purchases of marketable debt securities		(110,100,000)	(157,000,000.0)
Proceeds from sales of marketable debt securities		24,200,000	10,900,000
Proceeds from maturities of marketable debt securities		82,800,000
Other, net			(1,300,000)	2,500,000
Net cash used for investing activities		(426,100,000)	(546,600,000)	(608,200,000)
Cash Flows from Financing Activities:
Proceeds from issuance of debt			895,800,000
Repayments of debt and finance lease obligations		(1,500,000)	(923,400,000)	(151,300,000)
Financing costs paid			(8,300,000)
Common stock dividends paid		(299,600,000)	(298,700,000)	(268,100,000)
Shares withheld to cover employee restricted stock taxes		(10,500,000)	(8,200,000)	(7,900,000)
Net cash used for financing activities		(311,600,000)	(342,800,000)	(427,300,000)
Net increase in cash and cash equivalents		295,100,000	318,000,000.0	144,600,000
Cash and cash equivalents, beginning of year		679,500,000	361,500,000	216,900,000
Cash and cash equivalents, end of year		$ 974,600,000	$ 679,500,000	$ 361,500,000

[1] Includes “Additions to property, plant, and equipment” and excludes cash used for “Acquisitions of businesses, net of cash acquired” as reported on our Consolidated Statements of Cash Flows.