Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Cash flows from operating activities:
Net income	$ 72,474	$ 15,462	$ 53,394
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation, depletion, and amortization	44,137	42,384	41,116
Amortization of deferred financing costs in interest expense	967	790	962
Stock-based compensation expense (non-cash)	6,517	5,528	7,170
Amortization of pension and post-retirement costs	437	(151)	386
(Gain) loss on sale of property, plant, and equipment	(282)	466	344
Deferred income tax (benefit) expense	(12,957)	(9,850)	3,945
Impairment charges	0	10,472	14,141
Net pension curtailments and settlements	0	94	3,328
Changes in assets and liabilities, net of acquired assets and liabilities:
Decrease (increase) in accounts receivable	(30,490)	(707)	(23,933)
Decrease (increase) in inventory	(43,458)	(1,288)	20,485
Decrease (increase) in prepaid and other current assets	(3,855)	2,475	869
Increase (decrease) in accounts payable and accrued expenses	40,219	(21,877)	(18,575)
Increase (decrease) in unearned revenue	106	2,935	(2,538)
Increase (decrease) in interest and taxes payable	(220)	(157)	(805)
Increase (decrease) in unearned income due to customer prepayments	13,752	54,103	4,733
Domestic pension plan contributions	0	0	(4,500)
Other — net	2,894	378	(1,300)
Net cash provided by operating activities	90,241	101,057	99,222
Cash flows from investing activities:
Payments for acquisition, net of cash acquired	(392,240)	(130,715)	0
Payments for purchase of property, plant, and equipment	(102,910)	(67,274)	(24,251)
Payments for mine development	0	0	(2,277)
Proceeds from settlement of currency exchange contract	0	3,249	0
Proceeds from sale of property, plant, and equipment	881	33	44
Net cash used in investing activities	(494,269)	(194,707)	(26,484)
Cash flows from financing activities:
Proceeds from borrowings under revolving credit agreement, net	118,297	34,000	0
Proceeds from term loan	300,000	0	0
Repayment of long-term debt	(2,054)	(20,634)	(823)
Principal payments under finance lease obligations	(2,819)	(2,213)	(1,200)
Cash dividends paid	(9,697)	(9,257)	(8,856)
Deferred financing costs	(7,403)	0	(2,130)
Repurchase of common stock	0	(6,766)	(199)
Payments for withholding taxes for stock-based compensation awards	(3,318)	(2,221)	(4,846)
Net cash provided by (used in) financing activities	393,006	(7,091)	(18,054)
Effects of exchange rate changes	(394)	1,612	(322)
Net change in cash and cash equivalents	(11,416)	(99,129)	54,362
Cash and cash equivalents at beginning of period	25,878	125,007	70,645
Cash and cash equivalents at end of period	$ 14,462	$ 25,878	$ 125,007