CONDENSED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
OPERATING ACTIVITIES
Net income	$ 21,545	$ 110,447
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and depletion	28,692	22,233
Deferred income tax expense	3,276	27,984
Stock based compensation expense	1,733	1,194
Amortization of debt issuance costs and debt discount/premium, net	351	381
Accretion of asset retirement obligations	733	812
Loss on early extinguishment of debt	0	9,756
Changes in operating assets and liabilities:
Trade accounts receivable	(32,055)	(44,329)
Income tax receivable	0	297
Inventories	(17,326)	(10,823)
Prepaid expenses and other receivables	(235)	10,167
Accounts payable	15,614	10,640
Accrued expenses and other current liabilities	(3,538)	(15,133)
Other	2,232	2,782
Net cash provided by operating activities	21,022	126,408
INVESTING ACTIVITIES
Purchase of property, plant and equipment	(22,775)	(24,395)
Deferred mine development costs	(3,677)	(5,578)
Proceeds from sale of property, plant and equipment	0	234
Sale of short-term investments	14,733	0
Purchases of short-term investments	(8,500)	0
Net cash used in investing activities	(20,219)	(29,739)
FINANCING ACTIVITIES
Dividends paid	(2,598)	(2,606)
Borrowings under ABL Facility	70,000	0
Retirements of debt	0	(140,272)
Principal repayments of finance lease obligations	(3,833)	(1,957)
Common shares repurchased	0	(1,970)
Other	(1,012)	(527)
Net cash provided by (used in) financing activities	62,557	(147,332)
Net increase (decrease) in cash and cash equivalents and restricted cash	63,360	(50,663)
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	$ 256,743	$ 155,742