Investments classified as long-term consist of the following:


	Years Ended December 31,
	2019		2018
Available-for-sale investments:
Group insurance contracts	$	5,854	$	5,890
Cost method investments:
Minority interest in a private company(1)		—		4,400

	$	5,854	$	10,290

(1)	During 2019, the Company recognized $4,700 of impairment charges, which included an impairment of $4,400 of a long-term cost method investment in a private company.

The following table shows the gross unrealized gains and (losses) aggregated by investment category for

available-for-sale

investments:


As of December 31, 2019:	Cost		Gross Unrealized Gains		Gross Unrealized (Losses)			Estimated Fair Value
Short-term investments:
Available-for-sale investments:
Time deposits and certificates of deposit	$	13,045	$	—	$	—		$	13,045
Bankers’ acceptance drafts		4,043		—		—			4,043
Commercial paper		61,498		—		(293	)		61,205
U.S. treasury obligations		4,999		1		—			5,000
U.S. agency obligations		26,123		2		(1	)		26,124

	$	109,708	$	3	$	(294	)	$	109,417


As of December 31, 2019:	Cost		Gross Unrealized Gains		Gross Unrealized (Losses)		Estimated Fair Value
Long-term investments:
Available-for-sale investments:
Group insurance contracts	$	5,261	$	593	$	—	$	5,854


As of December 31, 2018:	Cost		Gross Unrealized Gains		Gross Unrealized (Losses)			Estimated Fair Value
Short-term investments:
Available-for-sale investments:
Time deposits and certificates of deposit	$	102	$	—	$	—		$	102
Bankers’ acceptance drafts		989		—		—			989
Asset-backed securities		9,121		1		(9	)		9,113
Commercial paper		19,504		—		(145	)		19,359
Corporate obligations		9,367		—		(15	)		9,352
U.S. treasury obligations		13,294		4		—			13,298
U.S. agency obligations		21,617		2		(6	)		21,613

	$	73,994	$	7	$	(175	)	$	73,826


As of December 31, 2018:	Cost		Gross Unrealized Gains		Gross Unrealized (Losses)		Estimated Fair Value
Long-term investments:
Available-for-sale investments:
Group insurance contracts	$	5,546	$	344	$	—	$	5,890

The tables above, which show the gross unrealized gains and (losses) aggregated by investment category for

available-for-sale

investments as of December 31, 2019 and 2018, reflect the inclusion within short-term investments of investments with contractual maturities greater than one year from the date of purchase. Management has the ability, if necessary, to liquidate any of its investments in order to meet the Company’s liquidity needs in the next 12 months. Accordingly, those investments with contractual maturities greater than one year from the date of purchase are classified as short-term on the accompanying balance sheets.

Interest income is accrued as earned. Dividend income is recognized as income on the date the security trades

“ex-dividend.”

The cost of marketable securities sold is determined by the specific identification method and realized gains or losses are reflected in income and were not material in 2019, 2018 and 2017.