Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Operating activities
Net income	$ 226,483	$ 157,179
Adjustments to reconcile to cash provided by operating activities:
Depreciation, depletion and amortization	92,027	94,536
Accretion on asset retirement obligations	20,977	22,826
Amortization of sales contracts, net	9,540	42,903
Prepaid royalties expensed	134	2,905
Deferred income taxes	(22,999)	6,069
Employee stock-based compensation expense	12,161	7,485
Gains on disposals and divestitures, net	(54)	(23,006)
Net loss resulting from early retirement of debt and debt restructuring	485	2,547
Amortization relating to financing activities	3,300	2,628
Changes in:
Receivables	(5,983)	(24,110)
Inventories	(34,918)	(13,102)
Accounts payable, accrued expenses and other current liabilities	(24,762)	5,103
Income taxes, net	(1,942)	(2,430)
Other	(8,334)	20,612
Cash provided by operating activities	266,115	302,145
Investing activities
Capital expenditures	(55,742)	(30,503)
Minimum royalty payments	(522)	(5,033)
Proceeds from disposals and divestitures	512	11,432
Purchases of short term investments	(140,097)	(191,327)
Proceeds from sales of short term investments	133,400	123,996
Investments in and advances to affiliates, net	(1,817)	(9,216)
Cash used in investing activities	(64,266)	(100,651)
Financing activities
Proceeds from issuance of term loan due 2024	0	298,500
Payments to extinguish term loan due 2021	0	(325,684)
Payments on term loan due 2024	(2,250)	(1,500)
Net payments on other debt	(10,286)	(5,992)
Debt financing costs	(1,009)	(10,043)
Net loss resulting from early retirement of debt and debt restructuring	(50)	(2,360)
Dividends paid	(23,966)	(16,763)
Purchases of treasury stock	(192,221)	(215,735)
Other	10
Cash used in financing activities	(229,772)	(279,577)
Decrease in cash and cash equivalents, including restricted cash	(27,923)	(78,083)
Cash and cash equivalents, including restricted cash, beginning of period	273,602	376,422
Cash and cash equivalents, including restricted cash, end of period	$ 245,679	$ 298,339