Investments in equity securities and available-for-sale debt securities are included in mine related assets, restricted and designated investments and other investments on the consolidated balance sheets. The cost, unrealized holding gains and losses, and fair value of equity and debt securities that do not have an allowance for credit losses were as follows as of March 31, 2026:


			Gross Unrealized Holding				Fair Value
	Cost		Gains		Losses
	(In thousands)
Available-for-sale debt securities:
Corporate and government bonds	$	1,958	$	44	$	—	$	2,002
Equity securities:
Equities and equity funds	43,347		79,899		—		123,246
Bond market funds	79,293		—		(6,239)		73,054
	122,640		79,899		(6,239)		196,300
Other	208		—		—		208
	$	124,806	$	79,943	$	(6,239)	$	198,510

The cost, unrealized holding gains and losses, and fair value of equity and debt securities that do not have an allowance for credit losses were as follows as of December 31, 2025:


			Gross Unrealized Holding				Fair Value
	Cost		Gains		Losses
	(In thousands)
Available-for-sale debt securities:
Corporate and government bonds	$	1,947	$	24	$	—	$	1,971
Equity securities:
Equities and equity funds	42,147		86,512		—		128,659
Bond market funds	78,577		—		(5,573)		73,004
	120,724		86,512		(5,573)		201,663
Other	88		—		—		88
	$	122,759	$	86,536	$	(5,573)	$	203,722

For the three months ended March 31, 2026, there were no sales proceeds on debt securities classified as available-for-sale. For the three months ended March 31, 2025, sales proceeds on debt securities classified as available-for-sale were $17.3 million. The cost of securities sold is based on the specific identification method. The realized losses for the three months ended March 31, 2025 were immaterial.


	March 31, 2026
	(In thousands)
Due through one year	$	461
Due after one year through five years	729
Due after five years	812
	$	2,002

Held-to-maturity debt securities have contracted maturity dates of one year or less and are included in cash and cash equivalents, restricted and designated cash and cash equivalents and short-term investments on the consolidated balance sheets. The amortized cost of held-to-maturity debt securities as of March 31, 2026 and December 31, 2025, was as follows:


	March 31, 2026		December 31, 2025
	(In thousands)
Corporate commercial paper	$	17,650	$	38,030
Money market funds	689,108		745,170
Treasuries	209,292		199,300
	$	916,050	$	982,500

Included in other investments on the consolidated balance sheets is the cash surrender value of life insurance policies of $1.7 million and $1.6 million, as of March 31, 2026 and December 31, 2025, respectively.

The MBPP provides financing to Western Fuels Association (Western Fuels) and Western Fuels-Wyoming, Inc. (WFW), a wholly owned subsidiary of Western Fuels, for mine development costs associated with coal deliveries to LRS. Basin Electric provides financing to Western Fuels and WFW for mine development costs associated with coal deliveries to DFS.

Notes receivable from WFW of $20.3 million and $20.8 million as of March 31, 2026 and December 31, 2025, respectively, are included in other investments, investments in associated companies and receivables, net on the consolidated balance sheets. Maturities range from July 2026 through May 2043, and the weighted average interest rate is 5.53 percent. The estimated fair value of these notes receivable as of March 31, 2026 and December 31, 2025 was $20.4 million and $21.0 million, respectively, based on the future cash flows discounted using the yield on a treasury note with a similar maturity.