CONDENSED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
OPERATING ACTIVITIES
Net income	$ 12,384	$ 235,928
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and depletion	50,848	47,911
Deferred income tax expense (benefit)	(1,154)	60,954
Stock based compensation expense	3,724	2,649
Amortization of debt issuance costs and debt discount/premium, net	708	696
Accretion of asset retirement obligations	1,466	1,624
Loss on early extinguishment of debt	0	9,756
Changes in operating assets and liabilities:
Trade accounts receivable	22,462	(22,435)
Income tax receivable	0	21,607
Inventories	(45,594)	(10,633)
Prepaid expenses and other receivables	(5,693)	8,510
Accounts payable	17,379	5,819
Accrued expenses and other current liabilities	(9,087)	(12,968)
Other	5,543	8,420
Net cash provided by operating activities	52,986	357,838
INVESTING ACTIVITIES
Purchase of property, plant and equipment	(48,754)	(52,100)
Deferred mine development costs	(8,731)	(12,069)
Proceeds from sale of property, plant and equipment	0	3,063
Sale of short-term investments	14,733	17,501
Purchases of short-term investments	(8,500)	(14,250)
Net cash used in investing activities	(51,252)	(57,855)
FINANCING ACTIVITIES
Dividends paid	(5,197)	(235,210)
Borrowings under ABL Facility	70,000	0
Repayments under ABL Facility	(30,000)	0
Retirements of debt	0	(140,272)
Principal repayments of finance lease obligations	(7,985)	(7,654)
Common shares repurchased	0	(1,970)
Other	(1,272)	(1,137)
Net cash provided by (used in) financing activities	25,546	(386,243)
Net increase (decrease) in cash and cash equivalents and restricted cash	27,280	(86,260)
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	$ 220,663	$ 120,145