INVESTMENTS

Equity and Debt Securities

The Company makes strategic investments in equity and debt securities of silver and gold exploration and development companies. These investments are classified as available-for-sale and are measured at fair value in the financial statements with unrealized gains and losses recorded in Other comprehensive income (loss).



	At December 31, 2017
In thousands	Cost		Gross Unrealized Losses			Gross Unrealized Gains		Estimated Fair Value
Equity Securities
Metalla Royalty & Streaming Ltd.	$	6,294	$	—		$	1,354	$	7,648
Corvus Gold Inc.	3,582		—			4,518		8,100
Almaden Minerals, Ltd.	3,125		(235		)	—		2,890
Northern Empire Resources Corp.	4,489		—			1,077		5,566
Rockhaven Resources, Ltd.	2,064		(193		)	—		1,871
Kootenay Silver, Inc.	738		—			1		739
Other	1,479		(453		)	405		1,431
Equity securities	$	21,771	$	(881	)	$	7,355	$	28,245

Debt Securities
Metalla Royalty & Streaming Ltd.	$	6,677	$	(85	)	$	—	$	6,592

Equity and debt securities	$	28,448	$	(966	)	$	7,355	$	34,837



	At December 31, 2016
In thousands	Cost		Gross Unrealized Losses		Gross Unrealized Gains		Estimated Fair Value
Kootenay Silver, Inc.	$	2,645	$	—	$	—	$	2,645
Silver Bull Resources, Inc.	233		—		783		1,016
Other	229		—		598		827
Equity securities	$	3,107	$	—	$	1,381	$	4,488

The Company performs a quarterly assessment on each of its equity and debt securities with unrealized losses to determine if the security is other than temporarily impaired. The Company recorded pre-tax other-than-temporary impairment losses of $0.4 million, $0.7 million and $2.3 million in the years ended December 31, 2017, 2016 and 2015, in Other, net. The following table summarizes unrealized losses on equity and debt securities for which other-than-temporary impairments have not been recognized and the fair values of those securities, aggregated by the length of time the individual securities have been in a continuous unrealized loss position, at December 31, 2017:



	Less than twelve months				Twelve months or more				Total
In thousands	Unrealized Losses		Fair Value		Unrealized Losses		Fair Value		Unrealized Losses		Fair Value
Equity securities	$	881	$	5,662	$	—	$	—	$	881	$	5,662
Debt securities	85		6,592		—		—		85		6,592

Restricted Assets

The Company, under the terms of its self-insurance and bonding agreements with certain banks, lending institutions and regulatory agencies, is required to collateralize certain portions of its asset retirement obligations. The Company has collateralized these obligations by assigning certificates of deposit that have maturity dates ranging from three months to a year to the applicable institutions or agencies. At December 31, 2017 and December 31, 2016, the Company held certificates of deposit and cash under these agreements of $20.8 million and $17.6 million, respectively. The ultimate timing of the release of the collateralized amounts is dependent on the timing and closure of each mine and repayment of the obligation. In order to release the collateral, the Company must seek approval from certain government agencies responsible for monitoring the mine closure status. Collateral could also be released to the extent the Company is able to secure alternative financial assurance satisfactory to the regulatory agencies. The Company believes the collateral will remain in place beyond a twelve-month period and has therefore classified these investments as long-term.