Fair Value Measurement (Tables)

6 Months Ended

Jun. 30, 2023

Fair Value Disclosures [Abstract]

Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis

The following tables summarize significant assets and liabilities measured at fair value in the condensed consolidated balance sheets on a recurring basis for each of the fair value levels (in thousands):

	Fair Value Measurement at Reporting Date Using
June 30, 2023	Level 1		Level 2		Level 3		Total
Cash equivalents
Money market funds	$	51,489	$	—	$	—	$	51,489
Total assets	$	51,489	$	—	$	—	$	51,489
Accrued and other current liabilities
Diesel collars	$	—	$	991	$	—	$	991
Commodity swaps	—		479		—		479
Total liabilities	$	—	$	1,470	$	—	$	1,470

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

Carrying Values and Estimated Fair Values of Financial Instruments Not Required to be Recorded at Fair Value

The carrying values and estimated fair values of financial instruments that are not required to be recorded at fair value in the condensed consolidated balance sheets were as follows:

		June 30, 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	$	36,556	$	35,458	$	65,943	$	64,584
Liabilities (including current maturities):
3.75% Convertible Notes (2)	Level 2	$	373,750	$	403,002	$	—	$	—
2.75% Convertible Notes (2)	Level 2	$	31,338	$	41,841	$	230,000	$	281,365
Credit Agreement - revolver (2)	Level 3	$	55,000	$	54,344	$	50,000	$	49,536