Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Cash flows from operating activities:
Net income	$ 74,823	$ 5,888	$ 95,702
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation, depletion, and amortization	69,074	68,676	61,644
Amortization of deferred financing costs in interest expense	1,887	1,714	1,712
Stock-based compensation expense (non-cash)	10,925	10,560	10,092
Amortization of pension and post-retirement costs	(154)	(307)	(1,318)
Loss on sale of property, plant, and equipment	282	1,201	20
Deferred income tax (benefit) expense	(5,103)	(16,598)	(7,005)
Impairment charges	0	73,201	0
Loss on asset disposal	0	6,412	0
Net pension curtailments and settlements	230	0	142
Changes in assets and liabilities, net of acquired assets and liabilities:
Decrease (increase) in accounts receivable	(25,790)	(3,723)	23,359
Decrease (increase) in inventory	(13,303)	(468)	(18,700)
Decrease (increase) in prepaid and other current assets	(15,101)	(11,345)	(22,663)
Increase (decrease) in accounts payable and accrued expenses	33,517	(15,757)	6,631
Increase (decrease) in unearned revenue	(15,204)	(24,692)	(17,361)
Increase (decrease) in interest and taxes payable	663	(2,619)	3,771
Increase (decrease) in unearned income due to customer prepayments	0	0	16,676
Other — net	(13,503)	(4,326)	(8,288)
Net cash provided by operating activities	103,243	87,817	144,414
Cash flows from investing activities:
Payments for acquisition, net of cash acquired	(19,500)	0	0
Payments for purchase of property, plant, and equipment	(53,279)	(68,649)	(110,550)
Payments for mine development	(26,288)	(12,159)	(9,326)
Proceeds from sale of property, plant, and equipment	932	1,203	654
Net cash used in investing activities	(98,135)	(79,605)	(119,222)
Cash flows from financing activities:
Proceeds from (repayments of) borrowings under credit facilities, net	33,890	45,692	8,065
Repayment of debt	(18,177)	(30,342)	(15,415)
Principal payments under finance lease obligations	(604)	(683)	(1,645)
Cash dividends paid	(11,510)	(11,087)	(10,621)
Deferred financing costs	(2,935)	(156)	0
Repurchase of common stock	(7,843)	0	0
Payments for withholding taxes for stock-based compensation awards	(2,642)	(7,610)	(5,234)
Net cash used in financing activities	(9,821)	(4,186)	(24,850)
Effects of exchange rate changes	1,681	(607)	(149)
Net change in cash and cash equivalents	(3,032)	3,419	193
Cash and cash equivalents at beginning of period	16,713	13,294	13,101
Cash and cash equivalents at end of period	$ 13,681	$ 16,713	$ 13,294