CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Cash flows from operating activities
Net income	$ 15,901	$ 58,766
Adjustments to reconcile net income to net cash provided by operating activities:
Deferred income taxes	5,608	10,823
Depreciation and amortization of property, plant and equipment	17,439	17,197
Stock-based compensation	719	803
Other	1,223	946
Cash provided (used) by changes in assets and liabilities:
Accounts receivable	15,418	(11,707)
Inventories	1,251	(10,817)
Prepaid insurance	5,158	3,687
Supplies, prepaid items and other	(4,455)	(6,253)
Accounts payable	(4,861)	10,003
Accrued interest	10,905	13,618
Other assets and other liabilities	(5,059)	(1,574)
Net cash provided by operating activities	59,247	85,492
Cash flows from investing activities
Expenditures for property, plant and equipment	(18,437)	(8,254)
Proceeds from short-term investments	88,707
Purchases of short-term investments	(133,660)	(89,311)
Other investing activities	11	51
Net cash used by investing activities	(63,379)	(97,514)
Cash flows from financing activities
Net proceeds from 6.25% senior secured notes		200,000
Payments on other long-term debt	(2,180)	(6,912)
Payments on short-term financing	(5,967)	(2,805)
Payments of debt-related costs, including extinguishment costs		(4,102)
Other financing activities	(2,541)	(2,004)
Net cash provided (used) by financing activities	(10,688)	184,177
Net increase (decrease) in cash and cash equivalents	(14,820)	172,155
Cash and cash equivalents at beginning of period	63,769	82,144
Cash and cash equivalents at end of period	$ 48,949	$ 254,299