Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Operating activities
Net income	$ 242,350	$ 226,483
Adjustments to reconcile to cash provided by operating activities:
Depreciation, depletion and amortization	82,199	92,027
Accretion on asset retirement obligations	15,411	20,977
Amortization of sales contracts, net	(77)	9,540
Deferred income taxes	13,680	(22,999)
Employee stock-based compensation expense	17,305	12,161
Gains on disposals and divestitures, net	(818)	(54)
Net loss resulting from early retirement of debt and debt restructuring	0	485
Amortization relating to financing activities	2,757	3,300
Preference Rights Lease Application settlement income	(39,000)	0
Changes in:
Receivables	(4,622)	(5,983)
Inventories	(46,073)	(34,918)
Accounts payable, accrued expenses and other current liabilities	1,569	(24,762)
Income taxes, net	32,440	(1,942)
Other	16,932	(8,200)
Cash provided by operating activities	334,053	266,115
Investing activities
Capital expenditures	(137,396)	(55,742)
Minimum royalty payments	(1,187)	(522)
Proceeds from disposals and divestitures	1,799	512
Purchases of short term investments	(158,578)	(140,097)
Proceeds from sales of short term investments	146,170	133,400
Investments in and advances to affiliates, net	(4,810)	(1,817)
Cash used in investing activities	(154,002)	(64,266)
Financing activities
Payments on term loan due 2024	(2,250)	(2,250)
Net payments on other debt	(12,077)	(10,286)
Debt financing costs	0	(1,009)
Net loss resulting from early retirement of debt and debt restructuring	0	(50)
Dividends paid	(22,264)	(23,966)
Purchases of treasury stock	(232,999)	(192,221)
Other	30	10
Cash used in financing activities	(269,560)	(229,772)
Decrease in cash and cash equivalents, including restricted cash	(89,509)	(27,923)
Cash and cash equivalents, including restricted cash, beginning of period	264,937	273,602
Cash and cash equivalents, including restricted cash, end of period	175,428	245,679
Cash and cash equivalents, including restricted cash, end of period
Cash and cash equivalents, including restricted cash, end of period	$ 264,937	$ 273,602