CONDENSED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
OPERATING ACTIVITIES
Net income (loss)	$ (2,050)	$ 280,949
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and depletion	78,813	73,652
Deferred income tax expense (benefit)	(9,268)	68,553
Stock based compensation expense	5,634	4,218
Amortization of debt issuance costs and debt discount/premium, net	1,125	1,024
Accretion of asset retirement obligations	2,198	2,436
Loss on early extinguishment of debt	0	9,756
Changes in operating assets and liabilities:
Trade accounts receivable	18,054	29,154
Income tax receivable	24,274	21,420
Inventories	(43,887)	(20,288)
Prepaid expenses and other receivables	(5,906)	7,080
Accounts payable	11,169	18,749
Accrued expenses and other current liabilities	(4,699)	645
Other	6,696	10,917
Net cash provided by operating activities	82,153	508,265
INVESTING ACTIVITIES
Purchase of property, plant and equipment	(72,059)	(78,366)
Deferred mine development costs	(13,257)	(18,398)
Proceeds from sale of property, plant and equipment	0	3,124
Sale of short-term investments	14,733	17,501
Purchases of short-term investments	(8,500)	(24,171)
Net cash used in investing activities	(79,083)	(100,310)
FINANCING ACTIVITIES
Dividends paid	(7,796)	(237,814)
Borrowings under ABL Facility	70,000	0
Repayments under ABL Facility	(30,000)	0
Retirements of debt, premium and fees	0	(140,272)
Principal repayments of finance lease obligations	(10,972)	(13,086)
Common shares repurchased	0	(12,546)
Other	(1,272)	(1,139)
Net cash provided by (used in) financing activities	19,960	(404,857)
Net increase in cash and cash equivalents and restricted cash	23,030	3,098
Cash and cash equivalents and restricted cash at beginning of period	193,383	206,405
Cash and cash equivalents and restricted cash at end of period	$ 216,413	$ 209,503