Note 9 - Fair Value Measurement (Tables)

3 Months Ended

Mar. 31, 2023

Notes Tables

Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis [Table Text Block]

	Fair Value Measurement at Reporting Date Using
March 31, 2023	Level 1		Level 2		Level 3		Total
Cash equivalents
Money market funds	$	42,821	$	—	$	—	$	42,821
Total assets	$	42,821	$	—	$	—	$	42,821
Accrued and other current liabilities
Diesel collars	$	—	$	934	$	—	$	934
Commodity swaps		—		138		—		138
Total liabilities	$	—	$	1,072	$	—	$	1,072

December 31, 2022
Cash equivalents
Money market funds	$	99,806	$	—	$	—	$	99,806
Other current assets
Commodity swaps		—		121		—		121
Total assets	$	99,806	$	121	$	—	$	99,927

Fair Value, by Balance Sheet Grouping [Table Text Block]

		March 31, 2023				December 31, 2022
(in thousands)	Fair Value Hierarchy	Carrying Value		Fair Value		Carrying Value		Fair Value
Assets:
Held-to-maturity marketable securities (1)	Level 1	$	56,329	$	55,272	$	65,943	$	64,584
Liabilities (including current maturities):
2.75% Convertible Notes (2)	Level 2	$	230,000	$	311,880	$	230,000	$	281,365
Credit Agreement - revolver (2)	Level 3	$	50,000	$	49,110	$	50,000	$	49,536