(in thousands)	September 30, 2021		December 31, 2020
Marketable equity securities	$	760,758	$	464,126
Non-marketable equity securities		379,548		217,104
Equity method investments		69,373		68,781
	$	1,209,679	$	750,011

See Note 1 Basis of Condensed Consolidated Financial Statements for further discussion of the balance sheet reclassifications of non-marketable equity securities and equity method investments to equity securities.

(in thousands)	Cost		Estimated fair value
September 30, 2021
Preferred stocks	$	16,810	$	16,944
Common stocks (1)		443,137		743,814
	$	459,947	$	760,758
December 31, 2020
Preferred stocks	$	22,163	$	19,479
Common stocks		354,157		444,647
	$	376,320	$	464,126

Net losses (realized and unrealized) of $16.1 million and net gains (realized and unrealized) of $27.2 million were recognized for the three and nine months ended September 30, 2021, respectively, as a result of changes in the fair values of marketable equity securities. Included in net gains during the three and nine months ended September 30, 2021 were net unrealized losses of $16.7 million and net unrealized gains $25.5 million, respectively, related to marketable equity securities still held at September 30, 2021. Net gains (realized and unrealized) of $26.0 million and $2.6 million were recognized for the three and nine months ended September 30, 2020, respectively, as a result of changes in the fair values of marketable equity securities. Included in net gains during the three and nine months ended September 30, 2020 were net unrealized gains of $26.1 million and $2.4 million, respectively, related to marketable equity securities still held at September 30, 2020. Net gains (realized and unrealized) are recognized in net realized investment gains/losses on the condensed consolidated statements of income.

(in thousands)	Cost			Unrealized gains	Carrying amount
September 30, 2021	$	198,155	$	181,393	$	379,548
December 31, 2020	$	200,858	$	16,246	$	217,104

A substantial majority of the Company’s investments in non-marketable equity securities are in private venture-stage companies that operate in the real estate industry and related industries, many of which offer technology-enabled products and services.

On September 1, 2021, Offerpad, Inc., a leading tech-enabled real estate solutions platform in which the Company maintains an ownership interest, and Supernova Partners Acquisition Company, Inc., a publicly traded special purpose acquisition company, completed their previously announced merger and combined to form Offerpad Solutions Inc. (“Offerpad”), a publicly traded company. The fair value of the Company’s investment in Offerpad as of September 30, 2021 was $280.3 million, which resulted in the Company recognizing an unrealized gain of $195.3 million for the three and nine months ended September 30, 2021. Effective September 1, 2021, the Company’s investment in Offerpad is classified within its marketable equity securities portfolio.

Included in investments in private venture-stage companies at September 30, 2021 are the Company’s investments in Orchard Technologies, Inc. with a cost and carrying amount of $41.0 million and $106.3 million, respectively, and Side, Inc. with a cost and carrying amount of $10.1 million and $73.8 million, respectively.

Unrealized gains of $79.4 million and $165.1 million were recognized during the three and nine months ended September 30, 2021, respectively, related to investments in private venture-stage companies for which transactions resulted in observable price changes. All such gains recognized during the nine months ended September 30, 2021 related to securities still held at September 30, 2021. Unrealized gains recognized on investments in private venture-stage companies for the three and nine months ended September 30, 2020 were $9.3 million. Net gains (realized and unrealized) are recognized in net realized investment gains/losses on the condensed consolidated statements of income.