Consolidated Statements of Cash Flows - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating activities:
Net income (loss)		$ 281,203	$ (67,258)	$ (657,691)
Loss from discontinued operations, net of tax	[1]	(3,783)	(300,354)	(834,080)
Income from continuing operations		284,986	233,096	176,389
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation, depletion and amortization		207,486	216,318	211,747
Deferred income taxes		(25,423)	(2,049)	(25,356)
Changes in current assets and liabilities, net of acquisitions:
Receivables		(108,255)	(25,641)	4,704
Inventories		9,135	2,433	2,265
Other current assets		(30,588)	(17,925)	60,182
Accounts payable		26,013	7,039	37,224
Other current liabilities		4,648	36,146	6,864
Other noncurrent changes		(18,790)	(26,459)	(10,240)
Net cash provided by continuing operations		349,212	422,958	463,779
Net cash provided by discontinued operations		98,799	39,251	198,053
Net cash provided by operating activities		448,011	462,209	661,832
Investing activities:
Capital expenditures		(341,382)	(388,183)	(536,832)
Net proceeds from sale or disposition of property and other		126,588	44,826	54,569
Investments		(1,608)	(1,396)	1,515
Net cash used in continuing operations		(216,402)	(344,753)	(480,748)
Net cash provided by discontinued operations		2,234	39,658	98,295
Net cash used in investing activities		(214,168)	(305,095)	(382,453)
Financing activities:
Issuance of long-term debt		140,812	309,064	345,920
Repayment of long-term debt		(217,394)	(315,647)	(566,498)
Proceeds from issuance of common stock		0	0	21,898
Dividends paid		(150,727)	(147,156)	(142,835)
Redemption of preferred stock		(15,600)	0	0
Repurchase of common stock		(1,684)	0	0
Tax withholding on stock-based compensation		(757)	(323)	0
Net cash used in continuing operations		(245,350)	(154,062)	(341,515)
Net cash provided by (used in) discontinued operations		0	(40,852)	85,785
Net cash used in financing activities		(245,350)	(194,914)	(255,730)
Effect of exchange rate changes on cash and cash equivalents		(1)	4	(225)
Increase (decrease) in cash and cash equivalents		(11,508)	(37,796)	23,424
Cash and cash equivalents - beginning of year		46,107	83,903	60,479
Cash and cash equivalents - end of year		$ 34,599	$ 46,107	$ 83,903

[1] Includes eliminations for the presentation of income tax adjustments between continuing and discontinued operations.