Investments classified as long-term consist of the following:


	September 30, 2019		December 31, 2018
Available-for-sale investments:
Group insurance contracts	$	5,746	$	5,890
Cost method investments:
Minority interest in a private company		4,400		4,400

	$	10,146	$	10,290

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

available-for-sale

investments:


As of September 30 , 2019:	Cost		Gross Unrealized Gains		Gross Unrealized (Losses)			Estimated Fair Value
Short-term investments:
Available-for-sale investments:
Time deposits and certificates of deposit	$	6,261	$	1	$	—		$	6,262
Bankers’ acceptance drafts		4,540		—		—			4,540
Commercial paper		45,342		—		(361	)		44,981
U.S. treasury obligations		3,601		1		—			3,602
U.S. agency obligations		29,460		4		(2	)		29,462

	$	89,204	$	6	$	(363	)	$	88,847


As of September 30 , 2019:	Cost		Gross Unrealized Gains		Gross Unrealized (Losses)		Estimated Fair Value
Long-term investments:
Available-for-sale investments:
Group insurance contracts	$	5,329	$	417	$	—	$	5,746


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 September 30, 2019 and December 31, 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.

The Company reviews and evaluates its investments for any indication of possible impairment. Based on this review, the Company has determined that the unrealized losses related to these investments at September 30, 2019 and December 31, 2018 were temporary.

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

“ex-dividend.”

The cost of marketable securities sold is determined by the specific identification method. Realized gains or losses are reflected in income and were not material for the nine months ended September 30, 2019 and 2018.