Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Operating activities:
Net income (loss)	$ 272,318	$ 281,203	$ (67,258)
Income (loss) from discontinued operations, net of tax	2,932	(3,783)	(300,354)
Income from continuing operations	269,386	284,986	233,096
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation, depletion and amortization	220,205	207,486	216,318
Deferred income taxes	59,735	(25,423)	(2,049)
Changes in current assets and liabilities, net of acquisitions:
Receivables	28,234	(108,255)	(25,641)
Inventories	(46,796)	9,135	2,433
Other current assets	(31,814)	(30,588)	(17,925)
Accounts payable	21,109	26,013	7,039
Other current liabilities	22,285	4,648	36,146
Other noncurrent changes	(38,521)	(18,790)	(26,459)
Net cash provided by continuing operations	503,823	349,212	422,958
Net cash provided by (used in) discontinued operations	(3,942)	98,799	39,251
Net cash provided by operating activities	499,881	448,011	462,209
Investing activities:
Capital expenditures	(568,230)	(341,382)	(388,183)
Acquisitions, net of cash acquired	(167,692)	0	0
Net proceeds from sale or disposition of property and other	26,100	126,588	44,826
Investments	(2,321)	(1,608)	(1,396)
Net cash used in continuing operations	(712,143)	(216,402)	(344,753)
Net cash provided by discontinued operations	1,236	2,234	39,658
Net cash used in investing activities	(710,907)	(214,168)	(305,095)
Financing activities:
Issuance of long-term debt	566,829	140,812	309,064
Repayment of long-term debt	(174,520)	(217,394)	(315,647)
Payments of stock issuance costs	(10)	0	0
Dividends paid	(154,573)	(150,727)	(147,156)
Redemption of preferred stock	0	(15,600)	0
Repurchase of common stock	(5,020)	(1,684)	0
Tax withholding on stock-based compensation	(2,330)	(757)	(323)
Net cash provided by (used in) continuing operations	230,376	(245,350)	(154,062)
Net cash used in discontinued operations	0	0	(40,852)
Net cash provided by (used in) financing activities	230,376	(245,350)	(194,914)
Effect of exchange rate changes on cash and cash equivalents	(1)	(1)	4
Increase (decrease) in cash and cash equivalents	19,349	(11,508)	(37,796)
Cash and cash equivalents - beginning of year	34,599	46,107	83,903
Cash and cash equivalents - end of year	$ 53,948	$ 34,599	$ 46,107